[volt-nuts] Matched resistors

Andreas Jahn Andreas_-_Jahn at t-online.de
Wed Jul 23 17:14:16 EDT 2014


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


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
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