A circuit includes an input channel array that includes a plurality of channels to receive a plurality of input signals and generate a plurality of channel output signals. A processor to processes the plurality of channel output signals from the input channel array. The processor and the input channel array are configured to operate in a sleep mode when all of the analog input signals are inactive or an active mode when at least one of the analog input signals is active. A secondary channel samples the plurality of input signals and generates a secondary output signal indicative of activity for at least one of the input signals. A secondary channel detector determines a level of signal activity for any of the input signals during the sleep mode based on the secondary output signal.