[time-nuts] Sub Pico Second Phase logger

[Joe Gwinn]

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>
>Message-ID: <494ADA0D.3060004 at xtra.co.nz>
>Content-Type: text/plain; charset=ISO-8859-1
>
>Joe
>
>
>  >>>      
>>>  [BG] Proposed test setup:
>>>  (preliminary to be refined)
>>>
>>>  Drive 2 sound card inputs in parallel with the same source.
>>>
>>>  Source amplitude:
>>>  Max sound card input -3dB
>>>    
>>
>>  What kind of dB?
>>
>>  
>Peak input signal voltage = 70% of sound card maximum peak input voltage.
>Just to leave some margin for gain tolerances.

OK.


>  >> 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.


>  >> Test frequencies:
>>>
>>>  100Hz
>>>
>>>  1kHz
>>>    
>>
>>  Why no 10 Hz?  (Well, 20 Hz.)
>>
>>  
>No particular reason other than some complications if a lamp stabilised
>oscillator is used.
>A diode soft (series R) clamped RC oscillator is more flexible in this
>regard.
>I'll also produce a circuit schematic for one of these oscillators.

Jim Williams' circuit would handle 10 Hz if I recall.


>  >> Sound card sample rate:
>>>
>>>  ~24KSPS
>>>    
>>
>>  I assume that this is the lowest rate supported, and certainly is overkill
>>  for 1 KHz.
>>
>>  
>It varies with the sound card.
>I just suggested that for a starting point in the discussion.
>
>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