Phase mod with PWM

[Don Tillman]

   From: Martin Czech <martin.czech at intermetall.de>
   Date: Tue, 7 Sep 1999 15:23:49 +0200 (MET DST)

   :::Is there a way of generating PWM without the phase modulation that seems
   :::to accompany it? I can understand that generating your PW from the saw
   :::output would generate a phase modulated signal. I believe, using a

   I don't know if I understand your problem, it seems that deep PWM causes
   a perception of FM, which you don't like.

I think I see the issue:

Most typically the PWM feature is built from a sawtooth wave, and the
rising point of the PWM waveform stays fixed while the falling point
moves back and forth in time with the PWM control voltage.  Depending
on the context our ears might hear this as the integral of the sum of
a fixed position positive pulse and a moving position negative pulse,
and that's the phase modulation effect you're hearing.

But if the PWM feature is built from a triangle wave instead of a
sawtooth wave, both the rising and falling points move in opposite
directions and you won't have that phase modulation effect.

This is the argument for having an assortment of PWM outputs on a VCO.
:-)

  -- Don