Re: [volt-nuts] Matched resistors
Hello Randy, until now you have not written about your design accuracy needs and about your environment conditions. (humidity + temperature controlled lab or industrial environment or simply your uncontrolled lab at home). In your measurements you should also regard humidity as a significant factor especially with resistors in plastic package like the LTC5400. Also the epoxy pcb is creating mechanical stress due to humidity to the resistors which can change the resistor value if not proper mechanical decoupled. (Difficult to mandage with SMD parts). I know that humidity is not easy to measure. And time constants are more in the range of 4-7 days which makes it even more time consuming. My personal opinion is that a LTC1043 based desing will perform better than a desing with SMD metal film resistors like the LTC5400. And a shoot out between vhd200 and LTC1043 would also be interesting depending on temperature range. By the way. The term TC tracking which is used by the resistor manufacturers may be not the same that you expect in a lab condition. Usually T.C. of a resistor is measured at 3 cardinal points -55 deg / 25 deg / 125 deg. T.C. is then calculated out of these 3 values. You probably want to have the dR / dT tracking around 25 degrees which is not specified with this method. So if you specifiy T.C. tracking you should do this with your temperature range. I hope that we will get feedback on your results some day. With best regards Andreas Am 26.07.2014 17:56, schrieb Randy Evans: I would like to thank all those you supplied ideas for matching resistors. I have decided to test three approaches for now, the first is using Vishay vhd200 hermetically sealed foil resistors (three each at around $26 each), the second is using LTC5400 resistor arrays, the third is a hybrid approach using a Vishay vhd200 for the most critical resistor pair and LTC5400 resistor arrays for the other two, and the fourth will likely be a LTC1043 switch capacitor doubler plus LTC5400s, although the latter is a lower priority. I plan on characterizing them over time and temperature to see the effects on output stability for the best approach considering cost, complexity, and accuracy. Should be interesting if it works. It's been taking longer than I wanted or hoped but there are only so many hours in the day and my day job is interfering with my play time. Thanks for the help, Randy On Fri, Jul 25, 2014 at 1:04 PM, Ivan.Cousins ijcous...@frontier.com wrote: Randy, You might want to look at: Digikey PN 749-1052-1-ND (qty 1, $0.89) or Digikey PN Y4485-5K/5KBCT-ND (qty 1, $22.93) Both parts are from Vishay. My advice is to build something and then measure that something. You are the best judge of your immediate design problem and measurement capabilities. I have found, after many years, that waiting for an Expert to hand you your answer does not work. No other Expert is as familiar with your present problem as you are. After a number of build-measure cycles, you may become the new Expert. If one waits for the ultimate answer then you may wait forever. The art of engineering is to get close enough. One can remain in the thinking stage forever, it can become an endless loop. Once you start the project by building and then measuring, you will be on your way to an answer, your answer. I am reminded of a saying everything is a transducer used here before. The interactions in this case are the usual temperature, stress-strain, humidity, resistor metal migration, etc. Notice that I did not include time, (long term drift), on purpose. It could be explained by one of the above or other, measurable quantity over a measurement interval. This is meant in the best spirit possible. Best of luck in your project. John C. ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/ mailman/listinfo/volt-nuts and follow the instructions there. ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there. ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
Re: [volt-nuts] Matched resistors
Andreas, The current environment is an uncontrolled home lab. Great variation in temperature and humidity, hence the primary design will use the vhd200 oil filled hermetic package resistor arrays. I plan on evaluating for stability and accuracy to see if I need to ovenize it to meet my voltage standard needs. I plan on building one version type with LTZ1000s and another with a LM399s for less demanding requirements. The LTZ1000 will definitely use the vhd200 resistor arrays and the LM399 may be able to use the LTC5400 resistor arrays (or LTC1043). The vhd200 is a leaded package so should have minimal mechanical stress on the package (hopefully). If necessary, and likely needed for the best stability, the circuit can be ovenized. Lots of testing to do. Randy On Sun, Jul 27, 2014 at 3:17 AM, Andreas Jahn andreas_-_j...@t-online.de wrote: Hello Randy, until now you have not written about your design accuracy needs and about your environment conditions. (humidity + temperature controlled lab or industrial environment or simply your uncontrolled lab at home). In your measurements you should also regard humidity as a significant factor especially with resistors in plastic package like the LTC5400. Also the epoxy pcb is creating mechanical stress due to humidity to the resistors which can change the resistor value if not proper mechanical decoupled. (Difficult to mandage with SMD parts). I know that humidity is not easy to measure. And time constants are more in the range of 4-7 days which makes it even more time consuming. My personal opinion is that a LTC1043 based desing will perform better than a desing with SMD metal film resistors like the LTC5400. And a shoot out between vhd200 and LTC1043 would also be interesting depending on temperature range. By the way. The term TC tracking which is used by the resistor manufacturers may be not the same that you expect in a lab condition. Usually T.C. of a resistor is measured at 3 cardinal points -55 deg / 25 deg / 125 deg. T.C. is then calculated out of these 3 values. You probably want to have the dR / dT tracking around 25 degrees which is not specified with this method. So if you specifiy T.C. tracking you should do this with your temperature range. I hope that we will get feedback on your results some day. With best regards Andreas Am 26.07.2014 17:56, schrieb Randy Evans: I would like to thank all those you supplied ideas for matching resistors. I have decided to test three approaches for now, the first is using Vishay vhd200 hermetically sealed foil resistors (three each at around $26 each), the second is using LTC5400 resistor arrays, the third is a hybrid approach using a Vishay vhd200 for the most critical resistor pair and LTC5400 resistor arrays for the other two, and the fourth will likely be a LTC1043 switch capacitor doubler plus LTC5400s, although the latter is a lower priority. I plan on characterizing them over time and temperature to see the effects on output stability for the best approach considering cost, complexity, and accuracy. Should be interesting if it works. It's been taking longer than I wanted or hoped but there are only so many hours in the day and my day job is interfering with my play time. Thanks for the help, Randy On Fri, Jul 25, 2014 at 1:04 PM, Ivan.Cousins ijcous...@frontier.com wrote: Randy, You might want to look at: Digikey PN 749-1052-1-ND (qty 1, $0.89) or Digikey PN Y4485-5K/5KBCT-ND (qty 1, $22.93) Both parts are from Vishay. My advice is to build something and then measure that something. You are the best judge of your immediate design problem and measurement capabilities. I have found, after many years, that waiting for an Expert to hand you your answer does not work. No other Expert is as familiar with your present problem as you are. After a number of build-measure cycles, you may become the new Expert. If one waits for the ultimate answer then you may wait forever. The art of engineering is to get close enough. One can remain in the thinking stage forever, it can become an endless loop. Once you start the project by building and then measuring, you will be on your way to an answer, your answer. I am reminded of a saying everything is a transducer used here before. The interactions in this case are the usual temperature, stress-strain, humidity, resistor metal migration, etc. Notice that I did not include time, (long term drift), on purpose. It could be explained by one of the above or other, measurable quantity over a measurement interval. This is meant in the best spirit possible. Best of luck in your project. John C. ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/ mailman/listinfo/volt-nuts and follow the instructions there. ___
Re: [volt-nuts] Matched resistors
I would like to thank all those you supplied ideas for matching resistors. I have decided to test three approaches for now, the first is using Vishay vhd200 hermetically sealed foil resistors (three each at around $26 each), the second is using LTC5400 resistor arrays, the third is a hybrid approach using a Vishay vhd200 for the most critical resistor pair and LTC5400 resistor arrays for the other two, and the fourth will likely be a LTC1043 switch capacitor doubler plus LTC5400s, although the latter is a lower priority. I plan on characterizing them over time and temperature to see the effects on output stability for the best approach considering cost, complexity, and accuracy. Should be interesting if it works. It's been taking longer than I wanted or hoped but there are only so many hours in the day and my day job is interfering with my play time. Thanks for the help, Randy On Fri, Jul 25, 2014 at 1:04 PM, Ivan.Cousins ijcous...@frontier.com wrote: Randy, You might want to look at: Digikey PN 749-1052-1-ND (qty 1, $0.89) or Digikey PN Y4485-5K/5KBCT-ND (qty 1, $22.93) Both parts are from Vishay. My advice is to build something and then measure that something. You are the best judge of your immediate design problem and measurement capabilities. I have found, after many years, that waiting for an Expert to hand you your answer does not work. No other Expert is as familiar with your present problem as you are. After a number of build-measure cycles, you may become the new Expert. If one waits for the ultimate answer then you may wait forever. The art of engineering is to get close enough. One can remain in the thinking stage forever, it can become an endless loop. Once you start the project by building and then measuring, you will be on your way to an answer, your answer. I am reminded of a saying everything is a transducer used here before. The interactions in this case are the usual temperature, stress-strain, humidity, resistor metal migration, etc. Notice that I did not include time, (long term drift), on purpose. It could be explained by one of the above or other, measurable quantity over a measurement interval. This is meant in the best spirit possible. Best of luck in your project. John C. ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/ mailman/listinfo/volt-nuts and follow the instructions there. ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
Re: [volt-nuts] Matched resistors
Tony, Sorry for not reading further. I will give it some thought. Interesting idea. Randy On Thu, Jul 24, 2014 at 5:13 AM, Tony Holt vn...@toneh.demon.co.uk wrote: Randy, On 24/07/2014 04:22, Randy Evans wrote: Tony, Your improvement factor of SQRT(n) assumes that each resistor in the group has random changes uncorrelated to all others in the group. For similar type resistors, I would think that is not likely to be true. Yes/,/ I'm well aware of that which is why I discussed that point further down in my post. It was a long post though so I don't blame you for getting bored and not getting that far! For shelf life stability it is likely that they all age in a similar way. Unless the resistors are in a hermetic package, humidity would impact all the resistors in a similar manner. Randy Exactly. Since they are being used in a 1:1 divider configuration, if they age in a similar way, the tracking ratio stability will be good. The reality however is that there will be some variance between components, and using multiple resisters will reduce that overall variance. Part of the variance between individual resisters will likely follow a Guassian distribution and thus the improvement factor for that element will be SQRT(N). Some of the variance will likely be due to random factors which have a rather different distribution, probably highly skewed with long tails, and thus the improvement probably won't be SQRT(N). My conjecture (ok random speculation) is that factors such as stress differences due to microcracking in the ceramic substrate or at the terminations may cause some of the latter. Nevertheless, even though part of the variance doesn't follow SQRT(N) the variance will still reduce by using multiple identical resisters (if there are enough*). The problem is knowing how much - it probably can only be determined by lengthy experimentation, unless some good empirical data can be obtained from manufacturers or research papers. Another complication is that I believe that thin film resistor stability and TCR characteristics improve as the resistance reduces. This is not usually reflected in the datasheet but using multiple resistors in series allows lower values to be used which may perform better. On the other hand, thermal EMF problems may increase proportionally. TCR tracking is much easier to measure, so it might be interesting to see how it improves with increasing numbers of resisters. However, I understand that ratio stability is likely to be a bigger problem than TCR tracking. The other end of the spectrum, using a single Vishay VHD foil divider is certainly the simplest; however bear in mind that Vishay's stated typical tracking TCR of .1ppm is just that, and the one that you buy may be anything but typical. And if you can work out the maximum tracking TCR from the VHD144/200 datasheet, you're a better man than I. My guess is that its probably better than .5ppm which is likely good enough for your application. But would it perform better than, say $30 worth of Vishay DFN, 3ppm 4-resister networks, 1 year shelf life ratio stability 20ppm? I don't know. Of course there's nothing to stop you using multiple VHDs if you can get them at a good price. Ebay maybe? *) If all resisters are identical expcept that 1 in a 100 is markedly different, then any 10 will have a good chance (90%) of being identical; using 100 will have a good chance (64%) that at least one is different and thus the overall error would be at least 1/100 of the difference. Tony H ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/ mailman/listinfo/volt-nuts and follow the instructions there. ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
Re: [volt-nuts] Matched resistors
Hello, the 50uV loss is plausible to me. But for the 100uVpp I have to ask for the measurement conditions. Is the source (reference) connected via (long cable) and supplied with another mains line or on the same pcb with the same power supply (or battery supplied). Was the pcb cleaned before measurement to keep leakage low? How much noise did the reference generate? 1uV output measurement is quite low with typical 0.6ppm/V of a buried zener multiplied by 2 and a amplifier with 1.6uVpp (referred to input). As every CMOS input is susceptible against noise (getting rectified over the input protection diodes) you can easily shift the input voltage by an offset due to RF noise. For LTC1043 inputs which are connected via external line I use a 1nF filter capacitor against ground to keep the influence of the RF noise low. With best regards Andreas Am 23.07.2014 02:40, schrieb Charles Steinmetz: Randy wrote: I agree that there are potentially some serious unknown issues with drift due to time and temperature due to changes in leakage current, charge injection, etc. I would think some serious characterization would be needed before this approach could be used. I have used LTC1043s in the voltage-multiplier configuration, and based on that experience I believe you will find there are too many surprises hiding there to reach your error budget. First, there are losses in the conversion -- IME, even when driving nothing but the non-inverting input of an LTC1050 chopper-stabilized opamp used as a follower, the output voltage of an LTC1043 doubler is quite a bit (50uV or more) less than [Vin * 2]. Second, the output of the 1043 + buffer is about 100x noisier than the output of the same reference followed by a non-inverting gain-of-two LTC1050 (on the order of 100uVp-p for the 1043 + buffer, about 1uVp-p for the non-inverting gain-of-two amplifier in a 10Hz bandwidth, IME). Also, the 1043 noise is not symmetrical, so different DC meters may give readings that differ by 50uV from one another. If you try the LTC1043, I'll be interested to see what you find. Best regards, Charles ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there. ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
Re: [volt-nuts] Matched resistors
Tony, Your improvement factor of SQRT(n) assumes that each resistor in the group has random changes uncorrelated to all others in the group. For similar type resistors, I would think that is not likely to be true. For shelf life stability it is likely that they all age in a similar way. Unless the resistors are in a hermetic package, humidity would impact all the resistors in a similar manner. Randy On Wed, Jul 23, 2014 at 6:36 PM, Tony vn...@toneh.demon.co.uk wrote: Randy, Have you considered using multiple identical resistors to reduce the variance? Depending on who you believe, you can reduce the variance of the overall resistance by SQRT(N) where N is the number of resistors in series/parallel. Its not that easy to create a good search query for this but here is one such explanation: http://paulorenato.com/joomla/index.php?option=com_content; view=articleid=109:combining-resistors-to-improve- tolerancecatid=4:projectsItemid=4 Ideally they should all come from the same batch - ie. manufactured by the same machine from the same batch of materials. Obviously there's no way to guarantee that without close liaison with the manufacturer (you did want 10 million parts at $.10 each didn't you!) but hopefully a set of resistors which come off the same reel would come close. The absolute value isn't important however, but 'statistical gain' will also apply to the TCR and stability of the overall divider. The following assumes that both factors are similarly improved by SQRT(N), but in fact they may be rather better than that. That80€ or $108 for one sealed Vishay foil divider will buy a lot of lower spec parts: Approx 12558 x Susumu RR0510P .5%, 25ppm 0402 (Digikey, $86/10k). 6279 in series and parallel in each leg of the 1:1 dividerhttp://media.digikey. com/photos/Susumu%20Photos/RR%200402%20SERIES.jpg might reduce the variance to 25ppm/SQRT(6279) = .32ppm. Can't see any spec for stability, but it may also improve similarly. Would take a while to solder them onto stripboard though! Slightly more sensible might be 1078 x TE Connectivity RP73 1%, 10ppm 1206 (Digikey, $100.18/1K). Stability .5% (no qualifers in datasheet) = 10ppm/SQRT(539) = .43ppm, stability = 215ppm Or 372 x KOA Speer RN731JTTD4021B5 .1%, 5ppm (Mouser, $29/100). Stability not on data sheet but typical endurance is +/- .02% for 1000 hrs @ 70C on/off 1.5hours/.5hours. = 5ppm/SQRT(138) = .37ppm, endurance = 14.7ppm (Stability should be rather better than that). Note that the Mouser part no. is for a 25ppm part but their manufacturer's part number is the 5ppm part as is the description. Also, the price is way too high for 25ppm parts. Or 28 x Susumu RG2012L .01%, 2ppm (Digikey, $39.6/10). Stability not quoted but typical Load Life is .01% (1000 x 1.5hours on/.5hours off at 85C) = 2ppm/SQRT(14) = .53ppm, endurance = 27ppm You could also use multiple resistor networks. Eg: 104 x Susumu RM2012B-103/103-PBVW10 .1%, 5ppm tracking, 2 resistors/device (Digikey $104/100). Stability not quoted, endurance 500ppm (1000 x 1.5hours on/.5hours off at 85C) = 5ppm/SQRT(104) = .49ppm, endurance = 49ppm 35 x TT Electronics SFN08B4701CBQLF7, .25%, 5ppm tracking 7 resistors/device (Digikey, $76/25) . Stability not quoted, high temperature exposure 1000ppm = 5ppm/SQRT(122) = .52ppm 33 x TT Electronics 668A1001DLF .5%, 5ppm tracking 8resistors/device (Digikey, $82/25). Stability not quoted, load life 1000ppm = 5ppm/SQRT(33 * 4) = .45ppm 16 x Vishay DFN .1%, 3ppm tracking with 4 resistors/device (Digikey, $5.24/1). Shelf life ratio stability is specced at 20ppm (1 year at 25C). (That may be a typical rather than a maximum - your parts may all be much worse than typical). The 3ppm tracking TCR may also be a typical figure as its headlined in a section titled 'TYPICAL PERFORMANCE' but in the specification table its not qualified with '(typical)' as they sometimes do in other datasheets. Its hard to tell. = 3ppm/SQRT(32) = .53ppm shelf life stability = 3.5ppm 5 x Vishay DSMZ metal foil dividers, .5ppm tracking max (probably performs rather better than this over restricted temperature range, but don't believe the Vishay typical figure of .1ppm/C) (Digikey, $22.93/1). Shelf life ratio stability not quoted but 'typical limit' for Load Life ratio stability is 50ppm (2000 hours at 70C). Who knows what a typical limit is? Again, probably best to treat Vishay 'typical' figures with a pinch of salt given the experience of another poster on volt-nuts. = .5ppm/SQRT(5) = .22ppm, load life = 22ppm Interestingly Digikey quote a price of only $5400 for 1k parts for the similar DSM divider (1ppm tracking), which is a huge difference from $22.93. Might be worth considering a bulk buy if there enough volt-nuts with the same problem. They aren't stocked though so that price might not be 'real'. However: 20 x Vishay DSM dividers, 1ppm (Digikey, $5400/1000) Load life ratio stability 'typical
Re: [volt-nuts] Matched resistors
Tony, I should have mentioned that I am primarily referring to stability, not accuracy. As i stated before, accuracy is relatively unimportant but stability is essential. Randy On Wed, Jul 23, 2014 at 8:22 PM, Randy Evans randyevans2...@gmail.com wrote: Tony, Your improvement factor of SQRT(n) assumes that each resistor in the group has random changes uncorrelated to all others in the group. For similar type resistors, I would think that is not likely to be true. For shelf life stability it is likely that they all age in a similar way. Unless the resistors are in a hermetic package, humidity would impact all the resistors in a similar manner. Randy On Wed, Jul 23, 2014 at 6:36 PM, Tony vn...@toneh.demon.co.uk wrote: Randy, Have you considered using multiple identical resistors to reduce the variance? Depending on who you believe, you can reduce the variance of the overall resistance by SQRT(N) where N is the number of resistors in series/parallel. Its not that easy to create a good search query for this but here is one such explanation: http://paulorenato.com/joomla/index.php?option=com_content; view=articleid=109:combining-resistors-to-improve- tolerancecatid=4:projectsItemid=4 Ideally they should all come from the same batch - ie. manufactured by the same machine from the same batch of materials. Obviously there's no way to guarantee that without close liaison with the manufacturer (you did want 10 million parts at $.10 each didn't you!) but hopefully a set of resistors which come off the same reel would come close. The absolute value isn't important however, but 'statistical gain' will also apply to the TCR and stability of the overall divider. The following assumes that both factors are similarly improved by SQRT(N), but in fact they may be rather better than that. That80€ or $108 for one sealed Vishay foil divider will buy a lot of lower spec parts: Approx 12558 x Susumu RR0510P .5%, 25ppm 0402 (Digikey, $86/10k). 6279 in series and parallel in each leg of the 1:1 dividerhttp://media.digikey. com/photos/Susumu%20Photos/RR%200402%20SERIES.jpg might reduce the variance to 25ppm/SQRT(6279) = .32ppm. Can't see any spec for stability, but it may also improve similarly. Would take a while to solder them onto stripboard though! Slightly more sensible might be 1078 x TE Connectivity RP73 1%, 10ppm 1206 (Digikey, $100.18/1K). Stability .5% (no qualifers in datasheet) = 10ppm/SQRT(539) = .43ppm, stability = 215ppm Or 372 x KOA Speer RN731JTTD4021B5 .1%, 5ppm (Mouser, $29/100). Stability not on data sheet but typical endurance is +/- .02% for 1000 hrs @ 70C on/off 1.5hours/.5hours. = 5ppm/SQRT(138) = .37ppm, endurance = 14.7ppm (Stability should be rather better than that). Note that the Mouser part no. is for a 25ppm part but their manufacturer's part number is the 5ppm part as is the description. Also, the price is way too high for 25ppm parts. Or 28 x Susumu RG2012L .01%, 2ppm (Digikey, $39.6/10). Stability not quoted but typical Load Life is .01% (1000 x 1.5hours on/.5hours off at 85C) = 2ppm/SQRT(14) = .53ppm, endurance = 27ppm You could also use multiple resistor networks. Eg: 104 x Susumu RM2012B-103/103-PBVW10 .1%, 5ppm tracking, 2 resistors/device (Digikey $104/100). Stability not quoted, endurance 500ppm (1000 x 1.5hours on/.5hours off at 85C) = 5ppm/SQRT(104) = .49ppm, endurance = 49ppm 35 x TT Electronics SFN08B4701CBQLF7, .25%, 5ppm tracking 7 resistors/device (Digikey, $76/25) . Stability not quoted, high temperature exposure 1000ppm = 5ppm/SQRT(122) = .52ppm 33 x TT Electronics 668A1001DLF .5%, 5ppm tracking 8resistors/device (Digikey, $82/25). Stability not quoted, load life 1000ppm = 5ppm/SQRT(33 * 4) = .45ppm 16 x Vishay DFN .1%, 3ppm tracking with 4 resistors/device (Digikey, $5.24/1). Shelf life ratio stability is specced at 20ppm (1 year at 25C). (That may be a typical rather than a maximum - your parts may all be much worse than typical). The 3ppm tracking TCR may also be a typical figure as its headlined in a section titled 'TYPICAL PERFORMANCE' but in the specification table its not qualified with '(typical)' as they sometimes do in other datasheets. Its hard to tell. = 3ppm/SQRT(32) = .53ppm shelf life stability = 3.5ppm 5 x Vishay DSMZ metal foil dividers, .5ppm tracking max (probably performs rather better than this over restricted temperature range, but don't believe the Vishay typical figure of .1ppm/C) (Digikey, $22.93/1). Shelf life ratio stability not quoted but 'typical limit' for Load Life ratio stability is 50ppm (2000 hours at 70C). Who knows what a typical limit is? Again, probably best to treat Vishay 'typical' figures with a pinch of salt given the experience of another poster on volt-nuts. = .5ppm/SQRT(5) = .22ppm, load life = 22ppm Interestingly Digikey quote a price of only $5400 for 1k parts for the similar DSM divider (1ppm tracking), which is a huge
Re: [volt-nuts] Matched resistors
Do you have easy, low cost access to an old Fluke 801 or 803 differential voltmeter? These meters have a Kelvin-Varley divider inside that is composed of strings of resistors that are highly matched in value and tempco. If I remember correctly, the highest decade is filled with a string of 40K resistors, each succeeding smaller decade value is 1/5 of the next higher decade, but all very well matched. They should all be very well aged by now too. (Just like wine... they get better with age). Perhaps you could mix match values to come up with suitable resistors for your project. If your project is a one-off deal, then perhaps that approach could prove viable. Cheers, Dave M From: Tony vn...@toneh.demon.co.uk Randy, Have you considered using multiple identical resistors to reduce the variance? Depending on who you believe, you can reduce the variance of the overall resistance by SQRT(N) where N is the number of resistors in series/parallel. Its not that easy to create a good search query for this but here is one such explanation: http://paulorenato.com/joomla/index.php?option=com_contentview=articleid=109:combining-resistors-to-improve-tolerancecatid=4:projectsItemid=4 Ideally they should all come from the same batch - ie. manufactured by the same machine from the same batch of materials. Obviously there's no way to guarantee that without close liaison with the manufacturer (you did want 10 million parts at $.10 each didn't you!) but hopefully a set of resistors which come off the same reel would come close. The absolute value isn't important however, but 'statistical gain' will also apply to the TCR and stability of the overall divider. The following assumes that both factors are similarly improved by SQRT(N), but in fact they may be rather better than that. That80? or $108 for one sealed Vishay foil divider will buy a lot of lower spec parts: ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
Re: [volt-nuts] Matched resistors
Andreas wrote: But for the 100uVpp I have to ask for the measurement conditions. Is the source (reference) connected via (long cable) and supplied with another mains line No or on the same pcb with the same power supply (or battery supplied). Yes. (And I have extensive design experience with ultra-low noise power supplies, decoupling, RFI prevention, and low-noise grounding.) Was the pcb cleaned before measurement to keep leakage low? Yes, it was freshly built and cleaned upon completion (vapor-phase), although that really has no bearing on commutation noise (charge injection) internal to the switched capacitor circuit, which is where all of the cyclical noise is generated. Can it be filtered out? Perhaps, but not easily without raising some other noise or drift problem. How much noise did the reference generate? 1uV output measurement is quite low with typical 0.6ppm/V of a buried zener multiplied by 2 and a amplifier with 1.6uVpp (referred to input). I was using the ADR4520 (1uVp-p noise in the 0.1-10Hz band), with post-filtering. When I said about 1uVpp output noise, I was thinking order of magnitude for purposes of comparison to 100uV, not precise value (which was more like 2-3uVpp). Best regards, Charles ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
Re: [volt-nuts] Matched resistors
yes, charge injection is an issue with all these switches and these also vary, in other words are somewhat unpredictable. now some of this may be compensated by a bigger c, but there are natural limits too. so for a production unit to sell, this would probably be a killer, but also for home-use, how do you predict the behavior over time? another option to use if you want to stay away from resistors is the pwm-solution as implemented by datron in e.g. their 4910. the pwm signal can today of course be done by uCs. Gesendet: Montag, 21. Juli 2014 um 22:28 Uhr Von: Bob Smither smit...@c-c-i.com An: Discussion of precise voltage measurement volt-nuts@febo.com Betreff: Re: [volt-nuts] Matched resistors On 07/17/2014 10:26 AM, Randy Evans wrote: Frank, The high cost is my concern, although high performance demands high price typically. I am trying to double the voltage reference from either an LM399 or LTZ1000, hence the need for precision matched resistors for a x2 non-inverting amplifier (using a LT1151 precision op amp). An alternative I am investigating is using the LTC1043 in a voltage doubling circuit as shown in Linear Technology app note AN 42, page 6, Figure 16. It states that Vout = 2xVin +/- 5 ppm. I am less concerned about the absolute accuracy than I am about the long term stability. I assume that a high quality capacitor is required (low leakage, low ESR, low dielectric absorbtion, etc.) but the circuit does not appear to be dependent on the absolute value of the capacitors. I'm not sure if the two 1uF caps need to be matched. If they do then that would be a show stopper. Does anyone have any experience using the LTC1043 in such a circuit? Hi Randy, There are some other error sources that might need to be considered when using the LTC1043. I have not used the LTC1043, but note that on the data sheet there is a small charge injection at each of the switch pins. In the multiply by 2 circuit shown on the data sheet they are using 1 ufd caps. Typical charge injection (depends on voltage level) is 8 pC. With the 1 ufd caps this is 8 uV. I assume there is some offsetting effect - but this might be a significant contributor to the 5 ppm error that is mentioned. There is also a 6 nA (typical) leakage mentioned. During the hold time ( about 1 msec) of the output 1 ufd cap this comes to 6 uV. Regards, Bob Smither ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there. ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
Re: [volt-nuts] Matched resistors
and yes, I forgot: only down-dividing of course, so to reach 10V, two LTZ1000 would be needed in series. advantage is that noise statistically is reduced by factor of about 1.4. formally also applies to drift. Gesendet: Montag, 21. Juli 2014 um 20:28 Uhr Von: Bob Smither smit...@c-c-i.com An: Discussion of precise voltage measurement volt-nuts@febo.com Betreff: Re: [volt-nuts] Matched resistors On 07/17/2014 10:26 AM, Randy Evans wrote: Frank, The high cost is my concern, although high performance demands high price typically. I am trying to double the voltage reference from either an LM399 or LTZ1000, hence the need for precision matched resistors for a x2 non-inverting amplifier (using a LT1151 precision op amp). An alternative I am investigating is using the LTC1043 in a voltage doubling circuit as shown in Linear Technology app note AN 42, page 6, Figure 16. It states that Vout = 2xVin +/- 5 ppm. I am less concerned about the absolute accuracy than I am about the long term stability. I assume that a high quality capacitor is required (low leakage, low ESR, low dielectric absorbtion, etc.) but the circuit does not appear to be dependent on the absolute value of the capacitors. I'm not sure if the two 1uF caps need to be matched. If they do then that would be a show stopper. Does anyone have any experience using the LTC1043 in such a circuit? Hi Randy, There are some other error sources that might need to be considered when using the LTC1043. I have not used the LTC1043, but note that on the data sheet there is a small charge injection at each of the switch pins. In the multiply by 2 circuit shown on the data sheet they are using 1 ufd caps. Typical charge injection (depends on voltage level) is 8 pC. With the 1 ufd caps this is 8 uV. I assume there is some offsetting effect - but this might be a significant contributor to the 5 ppm error that is mentioned. There is also a 6 nA (typical) leakage mentioned. During the hold time ( about 1 msec) of the output 1 ufd cap this comes to 6 uV. Regards, Bob Smither ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there. ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
Re: [volt-nuts] Matched resistors
I agree that there are potentially some serious unknown issues with drift due to time and temperature due to changes in leakage current, charge injection, etc. I would think some serious characterization would be needed before this approach could be used. One approach for the charge injection is to try and have the input voltage near Vdd/2 so the charge injection effects are nulled out. I'm trying to figure out how to do that for a X2 circuit. Any ideas? I talked to Vishay and they, of course, could do the resistors and I am awaiting a quote. They stated they would have to tune the vhd200 resistor pair to have a very low (0.2ppm/C) ratio stability . Doable but potentially very expensive. Unfortunately, the maximum value of the resistors is 20Kohms which would greatly increase the power dissipation of the resistors, not good for long term stability. Still working the issue. Randy On Tue, Jul 22, 2014 at 8:12 AM, acb...@gmx.de wrote: and yes, I forgot: only down-dividing of course, so to reach 10V, two LTZ1000 would be needed in series. advantage is that noise statistically is reduced by factor of about 1.4. formally also applies to drift. Gesendet: Montag, 21. Juli 2014 um 20:28 Uhr Von: Bob Smither smit...@c-c-i.com An: Discussion of precise voltage measurement volt-nuts@febo.com Betreff: Re: [volt-nuts] Matched resistors On 07/17/2014 10:26 AM, Randy Evans wrote: Frank, The high cost is my concern, although high performance demands high price typically. I am trying to double the voltage reference from either an LM399 or LTZ1000, hence the need for precision matched resistors for a x2 non-inverting amplifier (using a LT1151 precision op amp). An alternative I am investigating is using the LTC1043 in a voltage doubling circuit as shown in Linear Technology app note AN 42, page 6, Figure 16. It states that Vout = 2xVin +/- 5 ppm. I am less concerned about the absolute accuracy than I am about the long term stability. I assume that a high quality capacitor is required (low leakage, low ESR, low dielectric absorbtion, etc.) but the circuit does not appear to be dependent on the absolute value of the capacitors. I'm not sure if the two 1uF caps need to be matched. If they do then that would be a show stopper. Does anyone have any experience using the LTC1043 in such a circuit? Hi Randy, There are some other error sources that might need to be considered when using the LTC1043. I have not used the LTC1043, but note that on the data sheet there is a small charge injection at each of the switch pins. In the multiply by 2 circuit shown on the data sheet they are using 1 ufd caps. Typical charge injection (depends on voltage level) is 8 pC. With the 1 ufd caps this is 8 uV. I assume there is some offsetting effect - but this might be a significant contributor to the 5 ppm error that is mentioned. There is also a 6 nA (typical) leakage mentioned. During the hold time ( about 1 msec) of the output 1 ufd cap this comes to 6 uV. Regards, Bob Smither ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there. ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there. ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
Re: [volt-nuts] Matched resistors
Randy wrote: I agree that there are potentially some serious unknown issues with drift due to time and temperature due to changes in leakage current, charge injection, etc. I would think some serious characterization would be needed before this approach could be used. I have used LTC1043s in the voltage-multiplier configuration, and based on that experience I believe you will find there are too many surprises hiding there to reach your error budget. First, there are losses in the conversion -- IME, even when driving nothing but the non-inverting input of an LTC1050 chopper-stabilized opamp used as a follower, the output voltage of an LTC1043 doubler is quite a bit (50uV or more) less than [Vin * 2]. Second, the output of the 1043 + buffer is about 100x noisier than the output of the same reference followed by a non-inverting gain-of-two LTC1050 (on the order of 100uVp-p for the 1043 + buffer, about 1uVp-p for the non-inverting gain-of-two amplifier in a 10Hz bandwidth, IME). Also, the 1043 noise is not symmetrical, so different DC meters may give readings that differ by 50uV from one another. If you try the LTC1043, I'll be interested to see what you find. Best regards, Charles ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
Re: [volt-nuts] Matched resistors
Andreas, Since you are familiar with the LTC1043, do you know what stability over time and temperature one could expect for the X2 circuit, assuming a high quality low leakage capacitor was used? Since the circuit does not appear to be sensitive to the capacitor value, the primary change over time and temperature would be expected to be the switch resistance I would think. If the circuit were fed into a high impedance buffer (LTC1151), then I would expect the switch resistance to have minimal impact. What do you think? thanks, Randy On Sat, Jul 19, 2014 at 8:58 AM, Andreas Jahn andreas_-_j...@t-online.de wrote: Hello Randy, some information you will get on eevblog. (its much easier to post (larger) pictures there). Namely within the LTZ1000, LM399 and T.C. Measurements threads: http://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/ http://www.eevblog.com/forum/projects/lm399-based-10-v-reference/ http://www.eevblog.com/forum/projects/t-c-measurements-on- precision-resistors/ http://www.eevblog.com/forum/projects/oshw-24bit-adc- measurement-system-for-voltage-references/ http://www.eevblog.com/forum/projects/building-a-7-decade- voltage-calibrator/ http://www.eevblog.com/forum/projects/ppmgeek!-5-5-digit- dvm-volt-ref-cal-%28for-arduino-or-any-uc-w-spi%29/msg296127/#msg296127 With best regards Andreas Am 19.07.2014 16:33, schrieb Randy Evans: Andreas, Thanks for the information. Do you have the drift chart, etc. posted anywhere? that would be very interesting reading. Thanks, Randy On Fri, Jul 18, 2014 at 10:11 PM, Andreas Jahn andreas_-_j...@t-online.de wrote: Hello Randy, I think the only difference is in oscillator section (and thus power consumption) and of cause the TSSOP-package. The LTC1043 is easily available from stock e.g. from digikey. The LTC6943 is more difficult to get. Within the Keithley 2002 LTC1043 is used. http://www.eevblog.com/forum/testgear/keithley-2002-8-5- digit-dmm-review-and-teardown/ http://dev.xdevs.com/projects/kei2002/repository/entry/ photos/K1/small/K2002_1-2251.jpg I have added a drift chart with longterm drift data. Note: the drift is for the whole measurement arrangement. It consists of 3 7V references (2 LTZ1000A and 1 LM399) measured via a LTC1043 divider with a 24 bit LTC2400 ADC with temperature compensated voltage reference AD586LQ. So most of the drift is related to the AD586LQ reference. (X-axis is in days, Y-axis in ppm) I get around 2 ppm drift for the LTZ1000A over 1 year which I guess is mostly humidity related from the ADC printed cirquit board + AD586 reference drift and usually below 0.25 ppm standard deviation over 1000 hours. (42 days). All at unstabilized room temperature. I guess with resistors you will need ovenized temperature stabilisation to achieve this. with best regards Andreas Am 19.07.2014 05:57, schrieb Randy Evans: Andreas, That is good information, I appreciate it. I have contacted LT application support but they have yet to get back to me on my questions except they did recommend to use the LTC6943 instead of the LTC1043. Later generation I guess. I think i am going to try both the LTC6943 and the LT5400 resistor array and characterize them. The LT5400 matching ratio looks pretty good over temp (0.2ppm/C) but the absolute resistor change over temp is -10 to +25 ppm/C, a little larger than I would like for the circuit I am using. Randy On Thu, Jul 17, 2014 at 10:37 PM, Andreas Jahn andreas_-_j...@t-online.de wrote: Hello Randy, I am using the LTC1043 in 1/2 VIN or 1/3 VIN configuration. A matching of the caps is not necessary. In the 1/2 VIN or 1/3 VIN configuration a matching would give the advantage that the settling time of the cirquit is reduced. But in 2* VIN or inverting configuration a matching gives no advantage. So perhaps it is better to put a 1/2 VIN divider into a feedback loop. The most important point: you will need a low leakage buffer amplifier at the output. The caps should be low leakage foil capacitors. (polypropylene would be best). The ESR is negligible against the switch resistance of around 1000 Ohms And dielectric absorption would also affect only settling time. In 1/2 VIN configuration I am using cheap small mylar capacitors (WIMA MKS02) (isolation time constant is given only with 1250 sec (3000 sec typ)). Buffer amplifier is a LTC1050. The circuit is very stable over temperature (10 - 40 deg C). The absolute amplification error is usually some ppm lower than exact 2:1 value. (depends somewhat on the pinning which is used so I am not shure wether the pins are mixed up regarding the charge compensation) So I dont know wether the ±1 ppm is more a stability figure than a absolute value. Even polypropylene capacitors do not change the amplification error. With best regards Andreas Am 17.07.2014 17:26, schrieb Randy Evans: Frank, The high cost
Re: [volt-nuts] Matched resistors
Andreas, Of course, I would also expect the leakage currents to change over time/temperature and I would expect them to be the dominant error source. Randy On Mon, Jul 21, 2014 at 9:38 AM, Randy Evans randyevans2...@gmail.com wrote: Andreas, Since you are familiar with the LTC1043, do you know what stability over time and temperature one could expect for the X2 circuit, assuming a high quality low leakage capacitor was used? Since the circuit does not appear to be sensitive to the capacitor value, the primary change over time and temperature would be expected to be the switch resistance I would think. If the circuit were fed into a high impedance buffer (LTC1151), then I would expect the switch resistance to have minimal impact. What do you think? thanks, Randy On Sat, Jul 19, 2014 at 8:58 AM, Andreas Jahn andreas_-_j...@t-online.de wrote: Hello Randy, some information you will get on eevblog. (its much easier to post (larger) pictures there). Namely within the LTZ1000, LM399 and T.C. Measurements threads: http://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/ http://www.eevblog.com/forum/projects/lm399-based-10-v-reference/ http://www.eevblog.com/forum/projects/t-c-measurements-on- precision-resistors/ http://www.eevblog.com/forum/projects/oshw-24bit-adc- measurement-system-for-voltage-references/ http://www.eevblog.com/forum/projects/building-a-7-decade- voltage-calibrator/ http://www.eevblog.com/forum/projects/ppmgeek!-5-5-digit- dvm-volt-ref-cal-%28for-arduino-or-any-uc-w-spi%29/msg296127/#msg296127 With best regards Andreas Am 19.07.2014 16:33, schrieb Randy Evans: Andreas, Thanks for the information. Do you have the drift chart, etc. posted anywhere? that would be very interesting reading. Thanks, Randy On Fri, Jul 18, 2014 at 10:11 PM, Andreas Jahn andreas_-_j...@t-online.de wrote: Hello Randy, I think the only difference is in oscillator section (and thus power consumption) and of cause the TSSOP-package. The LTC1043 is easily available from stock e.g. from digikey. The LTC6943 is more difficult to get. Within the Keithley 2002 LTC1043 is used. http://www.eevblog.com/forum/testgear/keithley-2002-8-5- digit-dmm-review-and-teardown/ http://dev.xdevs.com/projects/kei2002/repository/entry/ photos/K1/small/K2002_1-2251.jpg I have added a drift chart with longterm drift data. Note: the drift is for the whole measurement arrangement. It consists of 3 7V references (2 LTZ1000A and 1 LM399) measured via a LTC1043 divider with a 24 bit LTC2400 ADC with temperature compensated voltage reference AD586LQ. So most of the drift is related to the AD586LQ reference. (X-axis is in days, Y-axis in ppm) I get around 2 ppm drift for the LTZ1000A over 1 year which I guess is mostly humidity related from the ADC printed cirquit board + AD586 reference drift and usually below 0.25 ppm standard deviation over 1000 hours. (42 days). All at unstabilized room temperature. I guess with resistors you will need ovenized temperature stabilisation to achieve this. with best regards Andreas Am 19.07.2014 05:57, schrieb Randy Evans: Andreas, That is good information, I appreciate it. I have contacted LT application support but they have yet to get back to me on my questions except they did recommend to use the LTC6943 instead of the LTC1043. Later generation I guess. I think i am going to try both the LTC6943 and the LT5400 resistor array and characterize them. The LT5400 matching ratio looks pretty good over temp (0.2ppm/C) but the absolute resistor change over temp is -10 to +25 ppm/C, a little larger than I would like for the circuit I am using. Randy On Thu, Jul 17, 2014 at 10:37 PM, Andreas Jahn andreas_-_j...@t-online.de wrote: Hello Randy, I am using the LTC1043 in 1/2 VIN or 1/3 VIN configuration. A matching of the caps is not necessary. In the 1/2 VIN or 1/3 VIN configuration a matching would give the advantage that the settling time of the cirquit is reduced. But in 2* VIN or inverting configuration a matching gives no advantage. So perhaps it is better to put a 1/2 VIN divider into a feedback loop. The most important point: you will need a low leakage buffer amplifier at the output. The caps should be low leakage foil capacitors. (polypropylene would be best). The ESR is negligible against the switch resistance of around 1000 Ohms And dielectric absorption would also affect only settling time. In 1/2 VIN configuration I am using cheap small mylar capacitors (WIMA MKS02) (isolation time constant is given only with 1250 sec (3000 sec typ)). Buffer amplifier is a LTC1050. The circuit is very stable over temperature (10 - 40 deg C). The absolute amplification error is usually some ppm lower than exact 2:1 value. (depends somewhat on the pinning which is used so I am not shure wether the pins are mixed up regarding the charge
Re: [volt-nuts] Matched resistors
On 07/17/2014 10:26 AM, Randy Evans wrote: Frank, The high cost is my concern, although high performance demands high price typically. I am trying to double the voltage reference from either an LM399 or LTZ1000, hence the need for precision matched resistors for a x2 non-inverting amplifier (using a LT1151 precision op amp). An alternative I am investigating is using the LTC1043 in a voltage doubling circuit as shown in Linear Technology app note AN 42, page 6, Figure 16. It states that Vout = 2xVin +/- 5 ppm. I am less concerned about the absolute accuracy than I am about the long term stability. I assume that a high quality capacitor is required (low leakage, low ESR, low dielectric absorbtion, etc.) but the circuit does not appear to be dependent on the absolute value of the capacitors. I'm not sure if the two 1uF caps need to be matched. If they do then that would be a show stopper. Does anyone have any experience using the LTC1043 in such a circuit? Hi Randy, There are some other error sources that might need to be considered when using the LTC1043. I have not used the LTC1043, but note that on the data sheet there is a small charge injection at each of the switch pins. In the multiply by 2 circuit shown on the data sheet they are using 1 ufd caps. Typical charge injection (depends on voltage level) is 8 pC. With the 1 ufd caps this is 8 uV. I assume there is some offsetting effect - but this might be a significant contributor to the 5 ppm error that is mentioned. There is also a 6 nA (typical) leakage mentioned. During the hold time ( about 1 msec) of the output 1 ufd cap this comes to 6 uV. Regards, Bob Smither attachment: smither.vcf___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
Re: [volt-nuts] Matched resistors
Andreas, Thanks for the information. Do you have the drift chart, etc. posted anywhere? that would be very interesting reading. Thanks, Randy On Fri, Jul 18, 2014 at 10:11 PM, Andreas Jahn andreas_-_j...@t-online.de wrote: Hello Randy, I think the only difference is in oscillator section (and thus power consumption) and of cause the TSSOP-package. The LTC1043 is easily available from stock e.g. from digikey. The LTC6943 is more difficult to get. Within the Keithley 2002 LTC1043 is used. http://www.eevblog.com/forum/testgear/keithley-2002-8-5- digit-dmm-review-and-teardown/ http://dev.xdevs.com/projects/kei2002/repository/entry/ photos/K1/small/K2002_1-2251.jpg I have added a drift chart with longterm drift data. Note: the drift is for the whole measurement arrangement. It consists of 3 7V references (2 LTZ1000A and 1 LM399) measured via a LTC1043 divider with a 24 bit LTC2400 ADC with temperature compensated voltage reference AD586LQ. So most of the drift is related to the AD586LQ reference. (X-axis is in days, Y-axis in ppm) I get around 2 ppm drift for the LTZ1000A over 1 year which I guess is mostly humidity related from the ADC printed cirquit board + AD586 reference drift and usually below 0.25 ppm standard deviation over 1000 hours. (42 days). All at unstabilized room temperature. I guess with resistors you will need ovenized temperature stabilisation to achieve this. with best regards Andreas Am 19.07.2014 05:57, schrieb Randy Evans: Andreas, That is good information, I appreciate it. I have contacted LT application support but they have yet to get back to me on my questions except they did recommend to use the LTC6943 instead of the LTC1043. Later generation I guess. I think i am going to try both the LTC6943 and the LT5400 resistor array and characterize them. The LT5400 matching ratio looks pretty good over temp (0.2ppm/C) but the absolute resistor change over temp is -10 to +25 ppm/C, a little larger than I would like for the circuit I am using. Randy On Thu, Jul 17, 2014 at 10:37 PM, Andreas Jahn andreas_-_j...@t-online.de wrote: Hello Randy, I am using the LTC1043 in 1/2 VIN or 1/3 VIN configuration. A matching of the caps is not necessary. In the 1/2 VIN or 1/3 VIN configuration a matching would give the advantage that the settling time of the cirquit is reduced. But in 2* VIN or inverting configuration a matching gives no advantage. So perhaps it is better to put a 1/2 VIN divider into a feedback loop. The most important point: you will need a low leakage buffer amplifier at the output. The caps should be low leakage foil capacitors. (polypropylene would be best). The ESR is negligible against the switch resistance of around 1000 Ohms And dielectric absorption would also affect only settling time. In 1/2 VIN configuration I am using cheap small mylar capacitors (WIMA MKS02) (isolation time constant is given only with 1250 sec (3000 sec typ)). Buffer amplifier is a LTC1050. The circuit is very stable over temperature (10 - 40 deg C). The absolute amplification error is usually some ppm lower than exact 2:1 value. (depends somewhat on the pinning which is used so I am not shure wether the pins are mixed up regarding the charge compensation) So I dont know wether the ±1 ppm is more a stability figure than a absolute value. Even polypropylene capacitors do not change the amplification error. With best regards Andreas Am 17.07.2014 17:26, schrieb Randy Evans: Frank, The high cost is my concern, although high performance demands high price typically. I am trying to double the voltage reference from either an LM399 or LTZ1000, hence the need for precision matched resistors for a x2 non-inverting amplifier (using a LT1151 precision op amp). An alternative I am investigating is using the LTC1043 in a voltage doubling circuit as shown in Linear Technology app note AN 42, page 6, Figure 16. It states that Vout = 2xVin ± 5 ppm. I am less concerned about the absolute accuracy than I am about the long term stability. I assume that a high quality capacitor is required (low leakage, low ESR, low dielectric absorbtion, etc.) but the circuit does not appear to be dependent on the absolute value of the capacitors. I'm not sure if the two 1uF caps need to be matched. If they do then that would be a show stopper. Does anyone have any experience using the LTC1043 in such a circuit? Thanks, Randy ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/ mailman/listinfo/volt-nuts and follow the instructions there. ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/ mailman/listinfo/volt-nuts and follow the instructions there. ___
Re: [volt-nuts] Matched resistors
Hello Randy, some information you will get on eevblog. (its much easier to post (larger) pictures there). Namely within the LTZ1000, LM399 and T.C. Measurements threads: http://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/ http://www.eevblog.com/forum/projects/lm399-based-10-v-reference/ http://www.eevblog.com/forum/projects/t-c-measurements-on-precision-resistors/ http://www.eevblog.com/forum/projects/oshw-24bit-adc-measurement-system-for-voltage-references/ http://www.eevblog.com/forum/projects/building-a-7-decade-voltage-calibrator/ http://www.eevblog.com/forum/projects/ppmgeek!-5-5-digit-dvm-volt-ref-cal-%28for-arduino-or-any-uc-w-spi%29/msg296127/#msg296127 With best regards Andreas Am 19.07.2014 16:33, schrieb Randy Evans: Andreas, Thanks for the information. Do you have the drift chart, etc. posted anywhere? that would be very interesting reading. Thanks, Randy On Fri, Jul 18, 2014 at 10:11 PM, Andreas Jahn andreas_-_j...@t-online.de wrote: Hello Randy, I think the only difference is in oscillator section (and thus power consumption) and of cause the TSSOP-package. The LTC1043 is easily available from stock e.g. from digikey. The LTC6943 is more difficult to get. Within the Keithley 2002 LTC1043 is used. http://www.eevblog.com/forum/testgear/keithley-2002-8-5- digit-dmm-review-and-teardown/ http://dev.xdevs.com/projects/kei2002/repository/entry/ photos/K1/small/K2002_1-2251.jpg I have added a drift chart with longterm drift data. Note: the drift is for the whole measurement arrangement. It consists of 3 7V references (2 LTZ1000A and 1 LM399) measured via a LTC1043 divider with a 24 bit LTC2400 ADC with temperature compensated voltage reference AD586LQ. So most of the drift is related to the AD586LQ reference. (X-axis is in days, Y-axis in ppm) I get around 2 ppm drift for the LTZ1000A over 1 year which I guess is mostly humidity related from the ADC printed cirquit board + AD586 reference drift and usually below 0.25 ppm standard deviation over 1000 hours. (42 days). All at unstabilized room temperature. I guess with resistors you will need ovenized temperature stabilisation to achieve this. with best regards Andreas Am 19.07.2014 05:57, schrieb Randy Evans: Andreas, That is good information, I appreciate it. I have contacted LT application support but they have yet to get back to me on my questions except they did recommend to use the LTC6943 instead of the LTC1043. Later generation I guess. I think i am going to try both the LTC6943 and the LT5400 resistor array and characterize them. The LT5400 matching ratio looks pretty good over temp (0.2ppm/C) but the absolute resistor change over temp is -10 to +25 ppm/C, a little larger than I would like for the circuit I am using. Randy On Thu, Jul 17, 2014 at 10:37 PM, Andreas Jahn andreas_-_j...@t-online.de wrote: Hello Randy, I am using the LTC1043 in 1/2 VIN or 1/3 VIN configuration. A matching of the caps is not necessary. In the 1/2 VIN or 1/3 VIN configuration a matching would give the advantage that the settling time of the cirquit is reduced. But in 2* VIN or inverting configuration a matching gives no advantage. So perhaps it is better to put a 1/2 VIN divider into a feedback loop. The most important point: you will need a low leakage buffer amplifier at the output. The caps should be low leakage foil capacitors. (polypropylene would be best). The ESR is negligible against the switch resistance of around 1000 Ohms And dielectric absorption would also affect only settling time. In 1/2 VIN configuration I am using cheap small mylar capacitors (WIMA MKS02) (isolation time constant is given only with 1250 sec (3000 sec typ)). Buffer amplifier is a LTC1050. The circuit is very stable over temperature (10 - 40 deg C). The absolute amplification error is usually some ppm lower than exact 2:1 value. (depends somewhat on the pinning which is used so I am not shure wether the pins are mixed up regarding the charge compensation) So I dont know wether the ±1 ppm is more a stability figure than a absolute value. Even polypropylene capacitors do not change the amplification error. With best regards Andreas Am 17.07.2014 17:26, schrieb Randy Evans: Frank, The high cost is my concern, although high performance demands high price typically. I am trying to double the voltage reference from either an LM399 or LTZ1000, hence the need for precision matched resistors for a x2 non-inverting amplifier (using a LT1151 precision op amp). An alternative I am investigating is using the LTC1043 in a voltage doubling circuit as shown in Linear Technology app note AN 42, page 6, Figure 16. It states that Vout = 2xVin ± 5 ppm. I am less concerned about the absolute accuracy than I am about the long term stability. I assume that a high quality capacitor is required (low leakage, low ESR, low dielectric absorbtion, etc.) but the circuit does not appear to be dependent on the absolute value of the
Re: [volt-nuts] Matched resistors
I figured out that VPG is Vishay Precision Group but I have not managed to identify the vhd hermetic divider. Could you point me to the location on the Vishay web site? Thanks, Randy On Fri, Jul 18, 2014 at 9:00 PM, Randy Evans randyevans2...@gmail.com wrote: I am not familiar with vpg or vhd terms. I assume the former is a company (European?) and the latter is a model type? Do you have a URL or other information to get followup information. The 0.1 ppm tracking is exactly what I am looking for and I don't need absolute accuracy. Thanks, Randy On Fri, Jul 18, 2014 at 12:00 AM, acb...@gmx.de wrote: randy, re. vpg: they offer an hermetic divider (vhd) with typ. 0.1ppm tracking of tempco. if you are ok with lowest available abs. accuracy it will be well priced, I remember having asked them for a price and it was below 50€ for standard lead time (which can be very long). it is also fair to assume it would age more homogeneously than two separate resistors, also you dont need to think about how to keep two resistors at the same temp. make sure each resistor is loaded with less than 10mw, otherwise aging may be above what the claim in their collateral. Gesendet: Donnerstag, 17. Juli 2014 um 04:40 Uhr Von: Frank Stellmach frank.stellm...@freenet.de An: volt-nuts@febo.com Betreff: [volt-nuts] Matched resistors Randy, resistor matched in T.C. are extremely expensive, as the manufacturer (or yourself) would have to select these from a batch of many samples. reistors with very small T.C. (1ppm/K) would do the job also, but they also need to be stable over time, in shelf life opereation mode, i.e. P10mW. That means, you need those hermetically sealed VHP202Z from Vishay, T.C. is typically 1ppm/K and they are stable to 2ppm over 5years. But they cost already 80€ each, depending on tolerance. I made a longterm observation of these and found these parameters confirmed. Frank ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there. ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there. ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
Re: [volt-nuts] Matched resistors
http://www.vishaypg.com/foil-resistors/list/product-63036/ http://www.vishaypg.com/doc?63036 Am 19.07.2014 06:07, schrieb Randy Evans: I figured out that VPG is Vishay Precision Group but I have not managed to identify the vhd hermetic divider. Could you point me to the location on the Vishay web site? Thanks, Randy On Fri, Jul 18, 2014 at 9:00 PM, Randy Evans randyevans2...@gmail.com wrote: I am not familiar with vpg or vhd terms. I assume the former is a company (European?) and the latter is a model type? Do you have a URL or other information to get followup information. The 0.1 ppm tracking is exactly what I am looking for and I don't need absolute accuracy. Thanks, Randy On Fri, Jul 18, 2014 at 12:00 AM, acb...@gmx.de wrote: randy, re. vpg: they offer an hermetic divider (vhd) with typ. 0.1ppm tracking of tempco. if you are ok with lowest available abs. accuracy it will be well priced, I remember having asked them for a price and it was below 50€ for standard lead time (which can be very long). it is also fair to assume it would age more homogeneously than two separate resistors, also you dont need to think about how to keep two resistors at the same temp. make sure each resistor is loaded with less than 10mw, otherwise aging may be above what the claim in their collateral. Gesendet: Donnerstag, 17. Juli 2014 um 04:40 Uhr Von: Frank Stellmach frank.stellm...@freenet.de An: volt-nuts@febo.com Betreff: [volt-nuts] Matched resistors Randy, resistor matched in T.C. are extremely expensive, as the manufacturer (or yourself) would have to select these from a batch of many samples. reistors with very small T.C. (1ppm/K) would do the job also, but they also need to be stable over time, in shelf life opereation mode, i.e. P10mW. That means, you need those hermetically sealed VHP202Z from Vishay, T.C. is typically 1ppm/K and they are stable to 2ppm over 5years. But they cost already 80€ each, depending on tolerance. I made a longterm observation of these and found these parameters confirmed. Frank ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there. ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there. ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there. ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
Re: [volt-nuts] Matched resistors
Frank, The high cost is my concern, although high performance demands high price typically. I am trying to double the voltage reference from either an LM399 or LTZ1000, hence the need for precision matched resistors for a x2 non-inverting amplifier (using a LT1151 precision op amp). An alternative I am investigating is using the LTC1043 in a voltage doubling circuit as shown in Linear Technology app note AN 42, page 6, Figure 16. It states that Vout = 2xVin +/- 5 ppm. I am less concerned about the absolute accuracy than I am about the long term stability. I assume that a high quality capacitor is required (low leakage, low ESR, low dielectric absorbtion, etc.) but the circuit does not appear to be dependent on the absolute value of the capacitors. I'm not sure if the two 1uF caps need to be matched. If they do then that would be a show stopper. Does anyone have any experience using the LTC1043 in such a circuit? Thanks, Randy On Wed, Jul 16, 2014 at 9:40 PM, Frank Stellmach frank.stellm...@freenet.de wrote: Randy, resistor matched in T.C. are extremely expensive, as the manufacturer (or yourself) would have to select these from a batch of many samples. reistors with very small T.C. (1ppm/K) would do the job also, but they also need to be stable over time, in shelf life opereation mode, i.e. P10mW. That means, you need those hermetically sealed VHP202Z from Vishay, T.C. is typically 1ppm/K and they are stable to 2ppm over 5years. But they cost already 80€ each, depending on tolerance. I made a longterm observation of these and found these parameters confirmed. Frank ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/ mailman/listinfo/volt-nuts and follow the instructions there. ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
Re: [volt-nuts] Matched resistors
Hello Randy, I am using the LTC1043 in 1/2 VIN or 1/3 VIN configuration. A matching of the caps is not necessary. In the 1/2 VIN or 1/3 VIN configuration a matching would give the advantage that the settling time of the cirquit is reduced. But in 2* VIN or inverting configuration a matching gives no advantage. So perhaps it is better to put a 1/2 VIN divider into a feedback loop. The most important point: you will need a low leakage buffer amplifier at the output. The caps should be low leakage foil capacitors. (polypropylene would be best). The ESR is negligible against the switch resistance of around 1000 Ohms And dielectric absorption would also affect only settling time. In 1/2 VIN configuration I am using cheap small mylar capacitors (WIMA MKS02) (isolation time constant is given only with 1250 sec (3000 sec typ)). Buffer amplifier is a LTC1050. The circuit is very stable over temperature (10 - 40 deg C). The absolute amplification error is usually some ppm lower than exact 2:1 value. (depends somewhat on the pinning which is used so I am not shure wether the pins are mixed up regarding the charge compensation) So I dont know wether the ±1 ppm is more a stability figure than a absolute value. Even polypropylene capacitors do not change the amplification error. With best regards Andreas Am 17.07.2014 17:26, schrieb Randy Evans: Frank, The high cost is my concern, although high performance demands high price typically. I am trying to double the voltage reference from either an LM399 or LTZ1000, hence the need for precision matched resistors for a x2 non-inverting amplifier (using a LT1151 precision op amp). An alternative I am investigating is using the LTC1043 in a voltage doubling circuit as shown in Linear Technology app note AN 42, page 6, Figure 16. It states that Vout = 2xVin ± 5 ppm. I am less concerned about the absolute accuracy than I am about the long term stability. I assume that a high quality capacitor is required (low leakage, low ESR, low dielectric absorbtion, etc.) but the circuit does not appear to be dependent on the absolute value of the capacitors. I'm not sure if the two 1uF caps need to be matched. If they do then that would be a show stopper. Does anyone have any experience using the LTC1043 in such a circuit? Thanks, Randy ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
Re: [volt-nuts] Matched resistors
Hi Randy; I would look at Visha Foil resistors http://www.vishaypg.com/docs/63120/hzseries.pdf Hope that helps. Cheers; Thomas Knox Date: Wed, 16 Jul 2014 17:44:10 -0700 From: randyevans2...@gmail.com To: volt-nuts@febo.com Subject: [volt-nuts] Matched resistors I am building a 10V voltage reference based on the LTZ1000 and the design is essentially done but I am looking for a pair of matched resistors that track very closely over temperature. The absolute value of the pair is not important, anything between 50K and 200K ohms would be ideal, but the matching ratio is very important. I looked at the 100K ohm LT5400 quad resistor array from Linear Technology but it has a worst case long term accelerated shelf life spec of 10 ppm (at 150C) matching ratio and long term matching ratio drift of 4ppm (at 70C). I would like something much tighter if possible since that would mean I likely don't need an oven for a couple of ppm worst case accuracy over time and temperature. I can make the LT5400 work but I would need to do temperature characterization and circuit compensation. Doable but undesirable. Does anyone have any ideas for a good ratio matched resistor pair, hopefully not too expensive? Thanks, Randy Evans ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there. ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
