Bi-pulse convertor (ON-topic)

[Magnus Danielson]

From: KA4HJH <ka4hjh at gte.net>
Subject: Bi-pulse convertor (ON-topic)
Date: Thu, 28 Dec 2000 04:19:59 -0500

> Here's a little project for everybody (and I keep thinking I already saw
> this in ElectroNotes or somewhere but...). This evening I got to fool
> around with the software synth Reaktor and I really like the harmonic sweep
> you get with the "bi-pulse" oscillator. This is basically a pulse wave
> where the positive and negative halves are generated separately and work in
> opposition. The top varies from 50% to 1% while the bottom varies from 50%
> to 99%, and vice versa.
> 
> The waveforms (converting from a ramp) look something like this:
> 
> 0% CV
> 
> ----------              +5
>           |
>           |
>           |              G
>           |
>           |
>            ----------   -5
> 
> 50% CV
> 
> -----                   +5
>      |
>      |
>       ---------          G
>                |
>                |
>                 -----   -5
> 
> 75% CV
> 
> ---                     +5
>    |
>    |
>     -------------        G
>                  |
>                  |
>                   ---   -5
> 
> Sounds like PWM but distinctly different. Should also work with a triangle
> input. Obviously this is a simple quantization problem, which has been
> discussed before. Anyone have a schematic?

Nope, but let's make one... this is done by using three op-amps and
four resistors...

                          |\
                      +---|+\    ___
 CV ------------------|-+ |  >--|___|-+
         ___     ___  | *-|-/    1k   |
     +--|___|-*-|___|-* | |/          |
     |   10k  |  10k  | |             *---- Out
     |        |  |\   | | |\          |
     |        +--|-\  | +-|+\    ___  |
Saw -*           |  >-+   |  >--|___|-+
     |        <|-|+/    +-|-/    1k
     |           |/     | |/
     +------------------+

That ougth to do it. Throw in buffers as required.

Cheers,
Magnus