[time-nuts] Software Sawtooth correction prerequisites?

Dr Bruce Griffiths bruce.griffiths at xtra.co.nz
Fri May 11 21:13:07 EDT 2007


Javier wrote:
> Tom Van Baak escribió:
>   
>> When someone finds a cheap single-shot 1 ns TIC-on-a-chip
>> please let me know.
>>
>>   
>>     
> www.acam.de
>
> Not very expensive although not cheap. I've some samples... but not yet 
> time to experiment with them.
>
> Regards,
>
> Javier, EA1CRB
>   
Javier

You still need some additional hardware like a synchroniser (shift 
register).
However this is indeed about as close as you will get to a single chip 
solution.

For an analog style TAC see attached schematic.
The required level shifting has been omitted for clarity.
NB current mode logic is employed where either P1 or P2 collector 
current is equal to alpha times P3's collector current.
Similarly for N1, N2, N3.
During reset both N2 and P2 are ON.
Diodes D1 and D2 conduct equal currents.
The collector current of N3 is 2x the collector current of P3.
The START input turns off N2 so that P2 charges C1.
The STOP input turns off P2 leaving the ramp voltage corresponding to 
the time between the START and STOP transitions stored on C1.
The opamp is then takes a few microsec to settle at which point its 
output can be sampled by an ADC.
When START and STOP both go to zero the capacitor voltage ramps down 
until it is clamped at 0V by D1 and D2.


Bruce
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