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 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. >>>>> >>>>> >>>> _______________________________________________ >>>> 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.
