Fast analog sw. as VC resistor

Mark Smart smart at nn.com
Fri Jan 3 00:46:52 CET 1997


> I realized last night that it would be better to use an analog switch in
> PARALLEL with a fixed resistor, rather than without a fixed resistor like
> in my previous post. If you use a bilateral switch like in the 4066 and two
> resitors, you can make a three-terminal pot very easily:
> 
> ------+----//////-------+------//////--------+---
>       |      R          |        R           |
>       |                 |                    |
>       +---------------o/  o------------------+
>                     1/4 4066
> 
> This way, you can vary the resistance to any fraction of R, and just use
> one PWM clock to control a pot.

I'm correcting myself again: the 4066 is not a quad SPDT switch, it's a
quad SPST switch. So to do the circuit above would require 1/2 of a 4066.
and an inverter for the clock. I was thinking of the 4053 2:1 analog mux.
1/3 of it could do the circuit above with no extra inverter.


************************************************
*     Mark Smart                               *
*     Network Technician                       *
*     University Communications Inc. (UCI)     *
*     smart at medusa.nn.com                      *
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