[time-nuts] Updated Shera controller

[Bruce Griffiths]

You can't predict the settling time of an opamp from its slew rate or 
its gain-bandwidth product.
The TS272 datasheet has no settling time spec whatsoever.
In this case, since there is no spec it needs to be measured.
Opamps with 2 or more cascaded gain stages like these are notorious for 
poor settling times.
10us is merely guesswork.
The settling time could well be much longer and it may depend on the 
input signal level.

Bruce



Richard H McCorkle wrote:
> FYI,
> The TS272/TS274 have a slew rate of 5.5v/us at unity gain, the max
> voltage on the cap is 2.7v in the new design, and the voltage is read
> <  10us after sample complete, so the buffer should have time to
> stabilize after the sample before being read.
>
> Richard
>
>
> Bruce wrote:
>    
>> Not really its both overkill as it doesnt timestamp, it only measures a
>> time interval and underkill in that theres no DAC.
>> There are also some concerns about the settling time of the TAC buffer
>> opamp which isnt strictly necessary for the lower resolution required in
>> this application.
>> PPS timestamping only needs a single TAC.
>>
>> Bruce
>>
>>
>>
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