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Operating a CMOS switching structure

Operating a CMOS switching structure

Operating a CMOS switching structure

Hi.  I am trying to implement a low cost (<$4 (1,000s of pieces)) solution to selectively (16 different levels)attenuate a line level audio signal similar to the way a wirewound potentiometer would be used.... I only have digital control capabilities available (the available digital pots that I have found can't handle the signal (0.5 W into a 45 ohm speaker)).

Tentatively, I have implemented four CMOS switches in parallel.  The structure of one is described below.  The question then, is: is there a known standard method of using a 0 to 3V digital system to turn both transistors on (+3V ---> -3 for the PMOS, +3 for the NMOS).  Both transistors are off at 0V.

Node 1: Line audio in, R1/1
Node 2: R1/2, D1/Anode, D2/Cathode
Node 3: D1/Cathode, Qn/Drain
Node 4: Qn/Source, Spkr/1, Qp/Source
Node 5: D2/Anode, Qp/Drain
Node 6: Qn/Gate (0V=OFF, +V=ON)
Node 7: Qp/Gate (0V=OFF, -V=ON)
*Nodes 6 & 7 are the subject of this question.. I would like to operate them simultaneously (0V=OFF, +V=ON).

** Three more identical structures will be used in parallel with the above described structure.  The 6/7 node will be controlled by a separate digital control line on each structure.
Beak --- 7/8/2000

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