[time-nuts] Fine print on HP 5334B

Dr Bruce Griffiths bruce.griffiths at xtra.co.nz
Thu Feb 22 23:56:46 EST 2007


Hal Murray wrote:
>> Every time I dig through the 5370 schematics, I think to myself
>> "wouldn't it be nifty to build a replacement plug-in card with a
>> modern fast CPU to run the instrument", but I try and stop myself
>> there. 
>>     
>
> Suppose you start with an FPGA on a PCI card.
>
> What sort of front end would you want?  What can you build with home/hacker 
> technology?
>
> My straw man is something to turn a digital signal out of a comparator into a 
> ramp that gets feed into an A/D clocked on the system's internal clock.  The 
> ramp needs to be a little over a cycle wide.
>
> Anybody got a circuit to make a linear ramp?
>
>   
Hal

Current mode ramp generators using long tailed pairs to switch the 
charging current for a capacitor are the time honoured approach for fast 
ramp generators.
This technique is still used today in IC designs with a mosfet used to 
discharge the capacitor rather than the more traditional Schottky diode 
pair.
NIST used a similar technique for the interpolators in their 
multichannel frequency measurement setup which monitors the stability of 
several standards against GPS.

Bruce



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