Apparatus for testing and measuring a. c. parameters of active elements connected incircuit

Claim 1

IN APPARATUS FOR MEASURING THE TRUE AC CURRENT FLOW THROUGH AN ACTIVE ELEMENT CONNECTED IN A CIRCUIT WITH UNKNOWN PASSIVE IMPEDANCES, THE COMBINATION OF A SIGNAL GENERATOR FOR PROVIDING A FIRST AC SIGNAL, AND A SECOND AC SIGNAL WHICH IS PERIODICALLY PHASE SWITCHED SO THAT IT IS IN-PHASE WITH SAID FIRST SIGNAL DURING A FIRST TIME INTERVAL AND 180 DEGREES OUT-OF-PHASE DURING A SECOND TIME INTERVAL; CIRCUIT MEANS FOR RENDERING THE ACTIVE ELEMENT OPERATIVE AT A DIFFERENT BIAS LEVEL DURING SAID FIRST TIME INTERVAL AS COMPARED TO SAID SECOND TIME INTERVAL; A PHASE DETECTOR CIRCUIT; CIRCUIT MEANS FOR APPLYING ON OF SAID AC SIGNALS TO SAID PHASE DETEFTOR CIRCUIT AS A SYNCHORIZING SIGNAL AND FOR APPLYING THE OTHER ONE OF SAID AC SIGNALS TO THE ACTIVE ELEMENT AS A TEST SIGAL; CIRCUIT MEANS RESPONSIVE TO THE AC CURRENT FLOW THROUGH THE ACTIVE ELEMENT AND UNKNOWN IMPEDANCES AS A RESULT OF SAID TEST SIGNAL, AND OPERATIVE TO PROVIDE A SIGNAL TO SAID PHASE DETECTOR CORRESPONDING TO SAID AC CURRENT FLOW; SAID PHASE DETECTOR BEING OPERATIVE TO PROVIDE AN OUTPUT SIGNAL OF ONE POLARITY IF THE SIGNALS APPLIED THERETO ARE ESSENTIALLY IN-PHASE, AND AN OUTPUT SIGNAL OF THE OPPOSITE POLARITY IF THE SIGNALS APPLIED THEREARE ESSENTIALLY 180 DEGREES OUT-OF-PHASE, TO THEREBY DERIVE A BIPOLAR OUTPUT SIGNAL; AND CIRCUIT MEANS RESPONSIVE TO THE AVERAGE VALUE OF SAID BIPOLAR SIGNAL.