Optically controllable S-type negative resistance presented by a combinational connection of photocoupled FET's

A negative resistance circuit constructed with a combinational connection of photocoupled FET's is proposed, which indicates optically controlled S-type negative resistance characteristics. The circuit can be used as a reciprocal switching element with two external light inputs and an application to optoelectronic flip-flop operation is presented. Moreover, a bidirectional S-type negative resistance circuit is proposed, in which three external light inputs may change widely the bidirectional S characteristics. Applications of the circuit, phase control operation of an alternatively applied voltage, and bilateral relaxation oscillation are demonstrated.