[time-nuts] Sub Pico Second Phase logger

Bruce Griffiths bruce.griffiths at xtra.co.nz
Fri Dec 19 16:50:46 EST 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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