[sdiy] problem with 13700 flter upper range

[Simon Brouwer]

harrybissell at wowway.com schreef:
> You really want to drive the OTA Gm inputs with a current source rather
> than voltage. Try looking for the EFM VCF1 that was adapted from the
> LM13700 data sheet... that would do it.

As the Gm pins of the OTA are connected to current mirrors the voltage on
them will be practically constant; about 0.7V above the negative rail. The
 control voltage range is *much* larger than the variation of that
voltage, therfore the Gm current will be proportional to the control
voltages with little error. I don't see how using a "real" current source
could improve much. An exponential converter however...


-- 
Vriendelijke groet,

Simon Brouwer
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