[time-nuts] Sub Pico Second Phase logger

[Joe Gwinn]

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.

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