[time-nuts] PICTIC II ready-made?

[David]

On Wed, 25 Apr 2012 21:26:25 +0200, Attila Kinali <attila at kinali.ch>
wrote:

>Hi Bruce,
>
>On Thu, 26 Apr 2012 07:15:41 +1200
>Bruce Griffiths <bruce.griffiths at xtra.co.nz> wrote:
>
>> If a suitable ADC is used the interpolator can be simplified 
>> considerably whilst improving its performance.
>
>Could you tell a little bit more about what a "suitable ADC" for
>a time interpolator is? And how exactly does it help to simplify
>the interpolator?

If you add a second lower current source or sink, then you can get
away with a LM311 class comparator and one fast timer channel in the
microcontroller.  The input pulse width charges the capacitor and the
timer counts how long it takes to slowly discharge.  Since the
conversion is integrating instead of sampling, it has better noise
immunity.

The Tektronix 2440 uses this technique to get about 50ps resolution.