[sdiy] 4-Quadrant VCA?

[Jay Schwichtenberg]

I wasn't able to find a schematic for this but I know they are out there somewhere.


One technique uses 2 OTAs and 2 half wave rectifiers. You feed the carrier into the + side of one OTA and the - side of the other. You connect the outputs together and buffer them. You feed the modulation into the half wave rectifiers, one being configured for the + side and the other configured for the - side of the modulation. You also invert the - side, convert both to current and drive the OTAs Iabc with those. So the + modulation goes through one OTA and the - modulation goes through the inverted one.


Even though the AD633 is expensive when you count parts and the cost of board space is the OTA solution going to be cheaper?


Jay S.


> On September 13, 2017 at 12:35 PM Tim Ressel <timr at circuitabbey.com> wrote:
> 
> 
>     Hey y'all,
> 
>     I am making a voltage controlled bipolar mixer, so I need a bipolar i.e. 4-quadrant VCA. So 2 channels mixing together with bipolar voltage control. Here is what I am thinking:
>     http://www.synthdiy.eu/files/BipolarVCA.png
>     A rectifier circuit will drive the 13700 Iabc port and a comparator will drive the switch.
> 
>     I know I could use AD633s but they are really pricey. Any other clever ways of pulling this off?
> 
>     -- 
>     --Tim Ressel
>     Circuit Abbey
>     timr at circuitabbey.com mailto:timr at circuitabbey.com
> 


 

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