Zero phase shift active element filter

Claim 1

A SIGNAL TRANSMISSION SYSTEM HAVING INPUT AND OUTPUT TERMINALS AND CHARACTERIZED BY A MINIMUM SHIFT IN THE PHASE OF THE VOLTAGE AT THE OUTPUT TERMINAL WITH RESPECT TO THE PHASE OF THE VOLTAGE AT THE INPUT TERMINAL WITH CHANGES IN FREQUENCY COMPRISING A FIRST FILTER SECTION, SAID INPUT TERMINAL PROVIDING THE INPUT TO SAID FIRST SECTION, A SECOND FILTER SECTION THE OUTPUT OF THE FIRST FILTER SECTION SERVING AS THE INPUT TO THE SECOND FILTER SECTION, SAID FIST FILTER SECOND HAVING TRANSMISSION CHARACTERISTICS WHICH MAY BE CHARACTERIZED BY A RESISTIVE AND A REACTIVE COMPONENT, SAID SECOND FILTER SECTION HAVING TRANSMISSION CHARCTERISTICS WHICH MAY BE CHARACTERIZED BY A RESISTIVE AND A REACTIVE COMPONENT, THE REACTIVE COMPONENTS OF SAID FIRST AND SECOND FILTER SECTION CHARACTERISTICS BEING EQUAL IN MAGNITUDE AND COMPRISING A REACTIVE GROUP, AND THE RESISTIVE COMPONENTS OF SAID FIRST AND SECOND FILTER SECTION TRANSMISSION CHARACTERISTICS BEING EQUAL IN MAGNITUDE AND COMPRISING A RESISTIVE GROUP, AND THE COMPONENTS OF ONE OF SAID GROUPS BEING OPPOSITE IN SIGN, THE OUTPUT OF SAID SECOND FILTER SECTION SERVING AS THE OUTPUT TO THE OUTPUT TERMINALS.