RE: echo timer web page

[msimon@xxxxxxxxxx (M. Simon)]

>
>I did not realize that the counter resolution was from an analog integrator.

Jeff never states this explicitly. At current state of the art there is no way 
to make a 75 MHz f/f clock at 2 GHZ. No amount of magic dust will make it so.

That leaves analog.

The rest is from an HP tutorial on counters.

>Thought it was from a higher crystal clock.
>Makes sense for getting the last fraction of counting ability out of your
>reference crystal's speed, then figuring the fractional amount slowly by
>measuring the stored voltage.

>I have a little electronics museum, and one of my prize milestone
>machines is a HP micro ammeter with a chopper amp.  It's chopper
>is black metal chopper wheel--not a semiconductor switch.
>John G

I worked on a spectrophotometer in '68 that had a chopper wheel.
And a 3 Decade logarithmic current input A/D converter. (Lots of
very precision resistors with odd values.) We looked at adding 
an Olivetti electronic calculator to the machine. But management couldn't 
see it. It was a neat calculator. It had a numeric printer and did
sines and anti-logs and all sorts of other good stuff.

Simon


>> -----Original Message-----
>> The circuit is not unbelievable if you know anything about
>> how modern frequency counters do fractional cycle
>> counts. Using A/D circuits. (ask HP).
>>
>> The only people mystified are the ignorant. (seems to be
>> a lot of that going around)
>>
>> A 16 bit A/D should resolve out to 1.2GHz.
>> A 256 bit A/D would work out to 19.2GHz.
>> About .05nS resolution.
>>
>> A current source is turned on at the end of the last input cycle
>> counted and
>> turned off at the end of the count period. Then the charge
>> accumulated on a
>> capacitor is measured.
>
>
Simon - http://www.tefbbs.com/spacetime/index.htm