[time-nuts] Happy Holidays

[Bruce Griffiths]

Bruce Griffiths wrote:
> Mark Sims wrote:
>   
>> Another possible thing to try is one of the Miller integrator chips that Tektronix used in their scopes and time base modules.  I seem to remember that at least one could yield 0.01% linearity.  The 5Bxx and 7Bxx modules for the 5000 and 7000 series scopes are available in vast quantities,  often for less than $10 (plus about that in shipping).  There is also an Ebay seller that has one of the chips in lots of 10...  search for "Tektronix miller".   I don't know what unit those chips were from.  They are in a TO5 type can,  not the usual DIP package.  To use a particular chip  you would need to do some reverse engineering from the appropriate module service manual.  The connections are usually fairly simple.
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>>   
>>     
> Yet another option is to use the simple TAC (figure 2) in:
> http://n1.taur.dk/permanent/frequencymeasurement.pdf
>
> The only drawback with this circuit is that the capacitor voltage at
> reset isn't zero.
> The capacitor reset voltage is also temperature dependent.
> Since the change in the capacitor voltage is proportional to the
> synchroniser delay, the solution to this is obvious:
> Measure the capacitor reset voltage with the ADC and subtract it from
> the capacitor voltage held on the capacitor after charging is terminated
> by the STOP input.
> Dedicated ACMOS (or equivalent low output impedance) flipflops can be
> used to drive the diode switches directly.
>
> Bruce
>
>
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>   
With a suitable charge redistribution ADC (one without resistive input
attenuators or an input buffer amplifier eg LTC1400, LTC1418 etc) the
buffer amplifier can be eliminated by connecting  the ADC input directly
to the ramp capacitor.

Bruce