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

Attila Kinali attila at kinali.ch
Sat Jul 7 12:31:47 EDT 2018


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

> Returning to the topic of what op-amp to use:
> Bert asked if the LT1793 is a good choice.  I suggested the LT1012 as 
> superior in the specific parameters that will provide best performance 
> in the HP circuit 
> (https://www.febo.com/pipermail/time-nuts/2018-February/108964.html). 
> Attila suggested the LTC6240HV.
> I continue to believe that the LT1012 is the best choice (or, 
> alternatively, the similar OP97 -- but the LT1012 would be my first choice).
> As Attila noted, the 6240 is limited to +/- 5v supplies.  I do not know 
> if the output voltage of the A9 ass'y needs to be able to swing beyond 
> +/- 5v, but I would not be inclined to change this without a lot of 
> careful thought (and adding another op-amp does not excite me).  But 
> really, that is not necessary.  Even if the 6240 could supply outputs up 
> to +/- 15v, the LT1012 would still be a better choice.

Coming back to an old thread... 
While looking for a suitable opamp for another application, I stumbled
across the ADA4077. It is basically the modern equivalent of the LT1012.
All but the input bias current and input voltage range specs are better:

(worst case where available, typical else)

			LT1012		ADA4077 (B grade)
Offset voltage		120µV		65µV
Offset tempco		1.5µV/°C	0.25µV/°C
Offset longterm		0.4µV/month	0.5µV/10kh (13months!)
Bias current		0.2nA		1.5nA
Noise voltage density	14nV/√Hz	7nV/√Hz
Low Freq Noise		0.5Vpp		0.25Vpp
GBW			0.8MHz		3.8MHz
Slew rate		0.2V/µs		1.2V/µs

The SO-8 packages are pin compatible, beside the missing offset compensation.

Unless you are using a chopper opamp for drift compensation, the ADA4077
might be worth considering. The higher GBW and slew rate would be benefitial
in an integrator application like the A9 board, as it improves linearity.

			Attila Kinali

<JaberWorky>	The bad part of Zurich is where the degenerates
                throw DARK chocolate at you.

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