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.
