Linear current source

[gstopp at fibermux.com]

     The VCA's in the ASM-1 are designed around a concept discussed in 
     EN#63, which is a technique devised by the famous Walter Jung in which 
     the 3080 is used as a current mirror array in the feedback loop of an 
     op-amp. The V- pin on the 3080 is driven by the op-amp's output. This 
     is about the simplest way to apply an accurate linear OTA control that 
     I've seen. Conveniently, the op-amp's (-) input is a summing node for 
     positive control voltages. The OTA output is a current so it needs an 
     I-to-V converter (another op-amp); however, if you are using multiple 
     VCA's to a single destination, you only need 1 I-to-V op-amp for the 
     lot.
     
     - Gene


______________________________ Reply Separator _________________________________
Subject: Re: Linear current source 
Author:  Magnus Danielson <e93_mda at snorke.it.kth.se> at ccrelayout
Date:    10/24/96 12:42 PM
     
>   Does anybody have any good linear voltage->current source for OTA 
>   circuits that can drive the OTA over it's full range?
     
Driveing OTAs has become a recent little problem of mine as well...
     
In the ASM-1 there is a op-amp and two diodes that drives an CA3080 with = 
linear
control. I haven't put that schematic on the web.... yet!
     
Magnus