[sdiy] PWM phaser problems

[Martin Czech]

1.: charge injection
2.: op amp bias current drops over appearant switch resistance

?

the 5meg pot experiment does not support 2, if the resistance
is compareable.


m.c.

:::X-Authentication-Warning: node12b53.a2000.nl: majordomo set sender to 
owner-synth-diy at node12b53.a2000.nl using -f
:::X-Sender: pfperry at popa.melbpc.org.au
:::Date: Sat, 03 Mar 2001 00:05:31 +1100
:::To: synth-diy at node12b53.a2000.nl
:::From: Paul Perry <pfperry at melbpc.org.au>
:::Subject: [sdiy] PWM phaser problems
:::
:::Building the PWM phaser from Elektor..
:::I find that as the PWM goes fully off, the bias on the 
:::filter section goes mad. I notice some other ckts are 
:::set so the PWM does not go fully off. I cant see why this should 
:::be a problem. Where is the weirdness?
:::If i replace the switched resistor by a 5 meg pot, all goes well.
:::If I replace the 4016 switch by a hand switch, I see that each 
:::time it is flipped there is some kind of bias problem appearing.
:::Anyone have light to shed on this?
:::The actual PWM production works well, though it is a problem that
:::the narrowest pulse width is not all that narrow, which limits range.
:::
:::paul perry melbourne austrlaia