Re: [volt-nuts] Matched resistors
Charles, For the design I am contemplating, the accuracy of the X2 in not important, only the stability. For example, if the output of the X2 is 50uV low, I don't care so long as its always 50 uV low +/- a few ppm over time and temperature. The noise could be filtered but its must also be stable. Based on what I am hearing, the switched capacitor multiplier doesn't look promising. Randy On Tue, Jul 22, 2014 at 5:40 PM, Charles Steinmetz wrote: > 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
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
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, 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" > > An: "Discussion of precise voltage measurement" > > 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.
[volt-nuts] 7071 noisy?
Hi Everyone, I have a problem. I bought a Solartron 7071 on Ebay. That Voltmeter seems working properly but I think it's too noisy. It passes Self Test and Initialize and the reading is consistent against a Weston Cell to the µV. But, when left with a short circuit as input the noise (maximum during 5 min) is: 0.2µV for 0.1V scale 0.4µV for 1V scale 8µV for 10V scale Is it acceptable? Thanks for your help. Bye, Jean-Louis ___ 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" > An: "Discussion of precise voltage measurement" > 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
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" > An: "Discussion of precise voltage measurement" > 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.
