a circuit which accepts an input signal of either positive or negative polarity and produces an output signal having an open circuit voltage similar in amplitude to the input signal amplitude but having a defined polarity . a plurality of switching elements , preferably mos transistors , are connected in a bridge circuit , the bridge circuit having a pair of input terminals responsive to the input signal and a pair of output terminals for providing the output signal , the switching elements being connected between the input and output terminals . each of the switching elements has a control input connected to one of the input terminals whereby each of the switching elements automatically opens or closes in response to the polarity of the input signal to maintain the defined polarity of the output signal .