Pulse VCO Help

[John Speth]

On Thursday, April 15, 1999 11:55 AM, Chris MacDonald 
[SMTP:macdonald at evenfall.com] wrote:
> I am trying to create a simple VCO which outputs very narrow pulses
> (microsecond range) at wide range of frequencies (0 to 10 khz at
> least).  It is not intended as an audio source so extreme stability is
> not an issue (it's for an experimental envelope generator).  I have come
> up with a circuit that works but I'm hoping there's a simpler way to do
> it.

You can use an XOR gate with some sort of delay line with whatever simple 
VCO you need to get a slim pulse from a square wave.  Simply run the square 
wave into one input of the XOR.  Also run the square wave into a delay line 
(made of 2 XOR gates in series).  Now run the output of the delay line into 
the other input of the XOR gate.  At the output you'll see a slim pulse 
with on-time equal to the delay line's delay time.  The downside is that 
you can't vary the pulse width.

Maybe you can experiment with a simple RC lowpass configuration and use a 
CMOS XOR gate which will allow you to vary the pulse width.

John Speth
Object Engineering, Inc
mailto:johns at oei.com