[sdiy] Oscillator jitter measurements

[Fredrik Carlqvist]

Hi all!



I have constructed a jitter measurement device (called the jitterbug,
actually ;-) with a resolution down to 100ns. I have done some initial
measurements on the synths I have at home. No conclusive results yet. But
the jitterbug works very well. My plan is to measure all different VCO
topologies I can get my hands on and present the results on a web page with
statistical analysis, distribution diagrams and everything. 

 

However, I need your help with the trigger circuit. It uses a LM311. There
is an image of the current design here:

 

http://www.minod.com/jitter/schemo.gif

 

The problem is that it has to be trimmed in with an oscilloscope before each
measurement as to remove oscillation and false triggers. My scope goes up to
20MHz and has no memory, so it is very difficult to see when the trig pulse
is ok. It is not impossible though. 

 

I want the trigger circuit to be useable without using a scope and without a
very pure input waveform if possible. Right now I have to hack into the VCO
core itself, since the slopes at the audio output of the synth often is not
very sharp. Most synths cannot open the filter enough it seems. 

 

So, for the benefit of science and our future VCO constructions please help
me with the trigger circuit!

 

 

Fredrik C

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