I am learning about VCOs. How can I add PWM to my current design.

Thread Starter

Emmanuel Galvan

Joined Aug 9, 2017
3
Hi all!

This is my first post here and I am looking for directions and will appreciate any pointers and or tips derived from your experience.

I'm currently working on a VCO for an audio application (I am a sound engineer and just finished a course on radio and amplification) however I do have some questions that I'd like some help with.

I designed a VCO using what it seems to be a typical op-amp configuration for this application (image attached).

With some tweaks and experimenting I've got a nice sounding square wave output. As I have experience with other oscillators, I kind of like how they sound with PWM. After perusing some schematics and looking at other VCOs I have concluded that, in order to add a PWM function to my oscillator, what I'd have to do is:

1) Breadboard a similar VCO to the one I've built.
2) Combine their outputs with an op amp in a comparator configuration.

Am I correct?
Am I complicating things?

This is a learning exercise for me and I am trying to challenge my current abilities so I can improve, however I thought it might be of benefit to seek some guidance here.

Thanks in advance!

Emmanuel.
 

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Thread Starter

Emmanuel Galvan

Joined Aug 9, 2017
3
You're on the right track.
But I don't understand the purpose of the PWM.
What signal will you use to modulate the PWM?
Well, as I understand (or trying to) I'll be using one oscillator to modulate the others's pulse width and thus changing the sound of the VCO. I am trying to achieve something similar to this:

 

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crutschow

Joined Mar 14, 2008
24,910
So you just connect one input of a comparator (such as the LM339/393) to the VCO triangle output, with the other input being the PWM modulator signal.
When mod input voltage equals 1/2 the triangle voltage, the PWM duty-cycle will be 50%.
 
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