[time-nuts] Sub Pico Second Phase logger
Bruce Griffiths
bruce.griffiths at xtra.co.nz
Fri Dec 19 21:50:46 UTC 2008
Joe
Joe Gwinn wrote:
> Bruce,
>
> At 3:54 AM +0000 12/19/08, time-nuts-request at febo.com wrote:
>
>> Message: 6
>> Date: Fri, 19 Dec 2008 16:54:12 +1300
>> From: Bruce Griffiths <bruce.griffiths at xtra.co.nz>
>> Subject: Re: [time-nuts] Sub Pico Second Phase logger
>> To: Discussion of precise time and frequency measurement
>> <time-nuts at febo.com>
>>
>> Joe
>> Joe Gwinn wrote:
>>
>>> This is from home. I'll not be at work until next year.
>>>
>>> At 11:48 PM +0000 12/18/08, time-nuts-request at febo.com wrote:
>>>
>>>
>>>> Message: 4
>>>> Date: Fri, 19 Dec 2008 12:17:33 +1300
>>>> From: Bruce Griffiths <bruce.griffiths at xtra.co.nz>
>>>> Subject: Re: [time-nuts] Sub Pico Second Phase logger
>>>> To: Discussion of precise time and frequency measurement
>>>>
>> >> <time-nuts at febo.com>
>> >>
>>
>>>> Joe
>>>>
>>>>
>>>> >>>
>>>>
>> >>
>> [snip]
>> >> >> Sources:
>>
>>>>
>>>>
>>>>>> 1) Wien bridge or equivalent (eg state variable oscillator with soft
>>>>>> clamping) relatively low distortion oscillator.
>>>>>>
>>>>>> 2) Buffered low pass filtered output of binary divider driven by a
>>>>>> crystal oscillator
>>>>>>
>>>>>>
>>>>>>
>>>> > RC oscillator sounds far simpler and more flexible.
>>>>
>>>> A Wien bridge using a lamp is perhaps the simplest.
>>>> I'll create a circuit schematics for this using an OPA2134 (dual lowish
>>>> noise JFET opamp).
>>>> One opamp for the oscillator one to drive the sound card (attenuation of
>>>> the oscillator output will be required for some sound cards and it is
>>>> desirable to have a low output impedance driver).
>>>>
>>>>
>>> Jim Williams of Linear Technology had a very good low-distortion AGC
>>> controlled Wein Bridge oscillator. If I recall, he used a photo-FET
>>> or the like as the servoed resistor in the bridge. There may be an
>>> application note on the LT website, but I saw it in a chapter of a
>>> book on analog circuitry, the chapter author being Jim W.
>>>
>>>
>>>
>>>
>> I have the application note.
>>
>
> LT App Note 43 is what JW mentions. Figure 47 is the key. (He also
> mentions App Note 5.)
>
> These cites are from the refs of "Max Wien, Mr. Hewlett, and a Rainy
> Sunday Afternoon", Jim Williams, Chapter 7 in "Analog Circuit Design
> -- Art, Science, and Personalities, edited by Jim Williams,
> Butterworth-Heinemann 1991. The relevant section of App Note 43
> seems to be shared with this chapter.
>
> It wasn't a photo-FET he used, it was a Vactec model VTL5C10
> optically (LED) driven CdS photocell.
>
>
Note for those (in Australia, NZ and Europe) who may want to replicate
that oscillator:
The VTL5C10 device is obtainable locally from RS Components.
> Most of it is here (what's missing is some history and the refs):
> <http://books.google.com/books?id=Il4xxTTyhbEC&pg=PA43&lpg=PA43&dq=Max+Wien,+Mr.+Hewlett,+and+a+Rainy+Sunday+Afternoon&source=bl&ots=jnHNItJrOF&sig=ZL_CB_yIdT0ZbsD7Ieu_CjVYJHk&hl=en&sa=X&oi=book_result&resnum=1&ct=result#PPA53,M1>.
>
>
>
>> >> For an AP192 the directly (without sample rate interpolation) available
>>
>>>> output sample rates are:
>>>>
>>>> 192, 96, 64, 48, 32, 8 KSPS.
>>>>
>>>>
>>> OK. I would start with 8 ksps. We will end up decimating below that
>>> anyway, except for 1 KHz test signals.
>>>
>>>
>>> Joe
>>>
>>>
>>>
>> I'll breadboard an oscillator over the holidays and take some samples.
>>
>
> A rainy-day activity for sure. In the Boston area, the issue is
> snow - a noreaster is just now starting, with a foot of snow expected.
>
> Joe
>
>
AFAIK it has never snowed here.
It does snow on the central NI Plateau but not usually in December.
I'll start with a diode limited (soft clamps - resistance in series with
diodes) oscillator and move to a lower distortion one if necessary.
Bruce
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