2/4 quadrant multiplier theory

[Fraser, Colin J]

> -----Original Message-----
> From: jorgen.bergfors at idg.se [mailto:jorgen.bergfors at idg.se]
> Sent: 03 September 1998 09:20
> To: moylan at eden.rutgers.edu; synth-diy at mailhost.bpa.nl
> Subject: Re: 2/4 quadrant multiplier theory
> 
> Actually 
> you can make a four 
> quadrant multiplier vith just one OTA, but don't ask me to 
> explain the theory 
> behind this. A circuit for this is in Barry Klein's book too.

I've seen a circuit elsewhere for this - it was quite simple.

Basically, the modulator input controls the level of the carrier signal
passing thru the OTA, and a 0v corresponds to half of the OTA range.
The output from the OTA is then mixed with half the input signal, but
inverted - so for a quiescent modulator input, there is no output.
As the modulator input increases, the carrier output of the OTA
increases, so the signal level increases at the output with positive
gain. As the modulator input decreases, the inverted signal at the
output becomes larger than the non-inverted output of the OTA, so the
carrier signal appears at the output with negative gain. Voila... ring
mod.

Colin f