[volt-nuts] Matched resistors

Charles Steinmetz csteinmetz at yandex.com
Wed Jul 23 23:59:25 EDT 2014


Andreas wrote:

>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

No

>or on the same pcb with the same power supply (or battery supplied).

Yes.  (And I have extensive design experience with ultra-low noise 
power supplies, decoupling, RFI prevention, and low-noise grounding.)

>Was the pcb cleaned before measurement to keep leakage low?

Yes, it was freshly built and cleaned upon completion (vapor-phase), 
although that really has no bearing on commutation noise (charge 
injection) internal to the switched capacitor circuit, which is where 
all of the cyclical noise is generated.  Can it be filtered 
out?  Perhaps, but not easily without raising some other noise or 
drift problem.

>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).

I was using the ADR4520 (1uVp-p noise in the 0.1-10Hz band), with 
post-filtering.  When I said "about 1uVpp" output noise, I was 
thinking order of magnitude for purposes of comparison to 100uV, not 
precise value (which was more like 2-3uVpp).

Best regards,

Charles





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