[sdiy] What is a quadrature oscillator good for?

[Don Tillman]

   > From: "jhaible" <jhaible at debitel.net>
   > Date: Wed, 10 Sep 2003 01:37:03 +0200
   > 
   > Unmodulated VCO running at 1000 Hz. Then add audio rate linear FM
   > from a second VCO, running at 500.1 Hz. (The .1 difference to f/2
   > shall provide some nice beating - just an example.)
   > Then increase the modulation index such that the _momentary_ frequency
   > of your modulated VCO changes from 1 Hz ... 1999 Hz. No problem,
   > but rather boring. Now increase the modulation index such that
   > the momentary frequency goes from -1 Hz ... 2001 Hz.
   > During this transition, are there no artefacts produced? No wavering pitch,
   > no waveform distortion?

I've performed similar tests, but not that one exactly.  I'll set it
up and try it soon, and maybe get a scope photo.

I don't expect to find any problems though.  This circuit really
doesn't mind going through zero Hz, bouncing off zero Hz, or sitting
at zero Hz.  Although sitting close to zero Hz does require trimming
the OTA offset voltages accurately.

  -- Don

-- 
Don Tillman
Palo Alto, California
don at till.com
http://www.till.com