Patent US 4,153,850

A source of alternating current signals is applied across the inverting and non-inverting input terminals of a voltage comparator circuit through a series bias resistor. Electrical circuitry including a supply potential source and the comparator circuit output terminal is effective to direct current flow through the bias resistor in respective first and second opposite directions while the comparator circuit is in the first and in the second operating conditions whereby the polarity of the potential generated across the bias resistor reverses with each change of operating condition of the comparator circuit.