One amplifier has two gain figures
Edited by Bill Travis
By Chuck Wojslaw, Catalyst Semiconductor, Sunnyvale, CA -- EDN, September 19, 2002
The single-supply circuit in Figure 1 is an inverting amplifier with two outputs—one for positive output voltages, VOUT(POS), and the other for negative output voltages, VOUT(NEG). Steering diodes D1 and D2 split the amplifier, IC1, output into the two output polarities relative to the 2.5V reference. The gain of the inverting amplifier for each of the two polarities features independent programming, using Catalyst's (www.catsemi.com) 100-tap, digitally programmable potentiometers DPP1 and DPP2. You configure the potentiometers as variable resistances and model them as (1–p)RPOT, where p represents the proportional position of the wiper as it moves from one end (p=0) of the DPP to the other end (p=1). RPOT is the potentiometer's end-to-end resistance. In terms of p, the gains of the circuit are
and
If R1POT, the gain values can be less than one, one, or greater than one. For the circuit values shown, you can program the two gains from approximately 1/10 to 10. If you characterize the potentiometer, the measured accuracy of the circuit is approximately 1%. This implementation of the circuit uses only six components and is appropriate for signal-processing applications.
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