Tue Jan 18 22:23:01 EST 2011


The CEM3320 datasheet[3] says the variable gain amplifiers are current
in, current out and the gain is set by a voltage.

  I_OUT = (I_REF - I_IN)  A_IO e^{-V_C / V_T}

I_REF flows through a feedback resistor from buffer output to input.

What would that circuit be?  Maybe a variant of the Basic
Transconductance Multiplier circuit leading to the a Gilbert cell in
[4] -- something using the translinear principle[5].

[1] http://curtiselectromusic.com/Product_Overview.html
[2] http://www.electricdruid.net/index.php?page=info.cem3320
[3] http://curtiselectromusic.com/uploads/CEM_3320_Long.pdf
[4] http://www.analog.com/static/imported-files/tutorials/MT-079.pdf
[5] http://en.wikipedia.org/wiki/Translinear_circuit