8.2.3 1-Bit PGA Operation

Using the internal inverting input switch that operates along with the power disable function can also allow a simple gain selection on a single input signal. Figure 88 shows an example gain select of either 1 V/V or 2 V/V from a single input to a single output. The logic disables both channels before turning one of them on to avoid high currents in both outputs to be active at the same time. If this approach is not possible, as in the simple switch shown in Figure 88, insert 100-Ω resistors inside the loop of each op amp output. A bipolar supply is shown in Figure 88, but any of the single-supply options are also possible. Any combination of gains can be implemented, but wide gain ranges show a larger change in signal bandwidth. This approach can be expanded to more than two gain settings. Testing with the circuit of Figure 88 showed no change in harmonic distortion; see Figure 18 and Figure 36.

Figure 88. 1-Bit PGA