[sdiy] OTA Iabc feeding

sleepy_dog at gmx.de sleepy_dog at gmx.de
Sat Sep 2 12:25:12 CEST 2017


 >  The voltage at the Iabc pin is V- + 2 diode drops.

Oh! That makes sense. Okay, looking at the circuit depicting what's 
going on *inside* the chip can help :-D
I see, that's a bit close to the neg. rail, for the cheap opamps I used 
so far anyway.

Thanks!

- Steve

Olivier Gillet wrote:
> The voltage at the Iabc pin is V- + 2 diode drops.
>
> So if you want to only use a resistor between your CV source and the
> Iabc pin, your CV source must be offset so that its minimum level (the
> value that will, for example, completely shut off your VCA) is exactly
> V- + 2 diode drops. That's not a very convenient voltage to deal with!
>
> It's more convenient to provide a current to the Iabc pin with a
> current source circuit - a circuit that is able to source a current
> proportional to the voltage at its input, irrespectively of the
> precise value of the voltage at the Iabc pin.
>




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