The single-supply circuit in Figure 1 is an inverting amplifier with two outputs—one for positive output voltages, V_OUT(POS), and the other for negative output voltages, V_OUT(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)R_POT, 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). R_POT is the potentiometer's end-to-end resistance. In terms of p, the gains of the circuit are

and

If R₁<R_POT, 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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