[time-nuts] V refs -- Bruce

[Bruce Griffiths]

Richard Moore wrote:
> Bruce, The 714 opamp provides gain in the Datron 1082, and I would  
> use one LTZ1000 (or two in parallel, rather than try to use them in  
> series). A while back I tried using two LM399s in series in a Fluke  
> 895, and really didn't like the results -- a single 399 with an amp  
> was better in every way I could measure. As an alternative to a  
> chopper like the 1151, I might consider an OPA27. I have used the now  
> unobtainable OPA111 in the past, and that was a superb DC amp; they  
> (TI) claim the OPA27 is as good.
>
> Dick Moore
>   
Dick

Replacing the 120 ohm resistor with a PJFET  (source connected to Zener
- Q1 base junction, drain connected to ground) the gate of which is
driven by an opamp to regulate the collector base voltage of Q1 at zero
volts, whilst using the standard zener bootstrap circuit to provide the
zener current can reduce the effect of lead resistance variations by a
factor of 10 or more over the standard LTZ1000 circuit.

Bruce