[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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