[time-nuts] Replacement A9 boards for the HP 5065A

Attila Kinali attila at kinali.ch
Mon Feb 26 09:53:21 EST 2018

On Sat, 24 Feb 2018 23:44:16 -0500
Charles Steinmetz <csteinmetz at yandex.com> wrote:

> Given the relatively low resistances at the op-amp inputs (10k ohms), 
> the ultra-low input "bias" (leakage) current of the 6240 is simply 
> unnecessary.  Any offset due to the input currents (within the general 
> range of any of these op-amps) is insignificant compared to the op-amp's 
> offset voltage.  Thus, offset voltage, offset voltage tempco, and offset 
> voltage long-tem drift are the critical parameters (as Poul-Henning 
> pointed out).  And here, the 1012 is clearly the best of the three.  In 
> addition to having the lowest input offset spec, the 1012 has guaranteed 
> maximum specifications for these important parameters.  The 6240 (for 
> good reason) is *not even rated* for long-term stability (drift). 
> (Long-term offset stability is a particular weakness of CMOS op-amps.)

Oh.. right, I didn't think about long term behaviour. Thanks for the correction!

BTW: How about using an LTC2057 then? Its input bias current  and
GBW spec is similar to the LT1012, but its offset voltage and drift
are far superior. Or would its charge injection noise be too large
for this application?

			Attila Kinali


It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
                 -- Miss Matheson, The Diamond Age, Neil Stephenson

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