[volt-nuts] Matched resistors
randyevans2688 at gmail.com
Sat Jul 19 10:33:14 EDT 2014
Thanks for the information. Do you have the drift chart, etc. posted
anywhere? that would be very interesting reading.
On Fri, Jul 18, 2014 at 10:11 PM, Andreas Jahn <Andreas_-_Jahn at t-online.de>
> Hello Randy,
> I think the only difference is in oscillator section (and thus power
> 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.
> 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
> Am 19.07.2014 05:57, schrieb Randy Evans:
>> That is good information, I appreciate it. I have contacted LT
>> support but they have yet to get back to me on my questions except they
>> recommend to use the LTC6943 instead of the LTC1043. Later generation I
>> 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.
>> On Thu, Jul 17, 2014 at 10:37 PM, Andreas Jahn <
>> Andreas_-_Jahn at t-online.de>
>> 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
>>> 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
>>> (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
>>> (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
>>> Am 17.07.2014 17:26, schrieb Randy Evans:
>>>> The high cost is my concern, although high performance demands high
>>>> typically. I am trying to double the voltage reference from either an
>>>> LM399 or LTZ1000, hence the need for precision matched resistors for a
>>>> non-inverting amplifier (using a LT1151 precision op amp). An
>>>> 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
>>>> 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?
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