Four multipliers for frequency shifters

[Kimmo Koli]

Well,
why not use two LM13700 to make four four-quadrant multipliers.
If the linearisation diodes are used then the four-quadrant operation
works independent of temperature unlike the 3080 multiplier.

Allmost a linearized Gilbert-cell like four-quadrant multiplier could be 
constructed by using two LM13700 VCAs in parallel:
 OTA1: X-signal to non-inverting input
       inverting input to ground
       Y-signal with a resistor to bias current input
 OTA2: X-signal to inverting input
       non-inverting input to ground
       a resistor to bias current input from ground
 Both OTA-outputs tied together = current summing.
If the linearization diodes are used the circuit is similar to "linearized"
Gilbert-cell with some extra current-mirror in the output.

Benefit from this circuit: a four quadrant multiplier without trimming.
I build a frequency doubler some five years ago like that and it worked fine.

I'm also considering building a VCA with a similar arrangement. Then the 
CV-reject could be small enough even without trimming and hopefully
some second order distortion reduction may occur.

Well, that's all,
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   Kimmo Koli                         Helsinki University of Technology 
   kimmo at ecdl.hut.fi                  Electronic Circuit Design Laboratory
   http://www.ecdl.hut.fi/~kimmo      Otakaari 5 A 
   Tel:  +358 9 451 2273              FIN-02150 Espoo
   Fax:  +358 9 451 2269              Finland 
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