2/4 quadrant multiplier theory

[jorgen.bergfors at idg.se]

Yes, you can make a four quadrant multiplier with two OTAs that are connected 
much the way you describe. See Barry Klein's book. 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.

/Jorgen





MIME:moylan at eden.rutgers.edu on 98-09-02 20.06.36
To:  synth-diy at mailhost.bpa.nl @ SMTP 
cc:  (bcc: Jorgen Bergfors/IDGSE)
Subject: 2/4 quadrant multiplier theory 

Okay, just sitting here thinking about something.
A 2 quadrant multiplier is essentially a VCA right?
And a 4 quadrant works similarly except that if the
control signal goes negative the polarity of the
signal is reversed (with respect to + control signals).
Would it be possible to get similar results by using
a Voltage Controlled Mixer mixing 2 signals 180 degrees
out of phase.  Assuming a certain bias added to the 
"control" signal, at 0 input we'd have 0 output (equal
mix of signal and inverted signal), if the control
swings positive, we get more straight signal, if it 
swings negative, we get more inverted signal.  Am I 
missing anything?  Thanks.  dave moylan