Hybrid electrometer amplifier having protective means in feedback path to limit positive excursions of negative feedback signal

Claim 1

A HYBRID CIRCUIT FOR MEASURING WEAK DIRECT-CURRENT SIGNALS COMPRISING: AN INITIAL AMPLIFYING STAGE HAVING AN EVACUATED VOLTAGE AMPLIFYING DEVICE INCLUDING AN ELECTRONEMISSIVE CATHODE, A CONTROL ELECTRODE AND AN ANODE; A PLURALITY OF DIRECTLY COUPLED SUCCEEDING AMPLIFYING STAGES EACH HAVING ONLY A SINGLE ACTIVE AMPLIFYING ELEMENT, SAID ELEMENT BEING A SEMICONDUCTOR DEVICE; NEGATIVE FEEDBACK MEANS CONNECTED FROM THE OUTPUT OF THE FINAL STAGE OF SAID SUCCEEDING AMPLIFYING STAGES TO THE INPUT OF SAID INITIAL STAGE, SAID NEGATIVE FEEDBACK MEANS BEING ADAPTED TO RETURN ESSENTIALLY ALL OF THE OUTPUT SIGNAL ENERGY OF SAID FINAL STAGE TO THE INPUT OF SAID INITIAL STAGE TO ESSENTIALLY NULL-BALANCE ANY EXTERNAL POSITIVE SIGNAL TO BE MEASURED THAT IS APPLIED TO THE INPUT OF SAID INITIAL STAGE; MEANS COUPLED TO SAID NEGATIVE FEEDBACK MEANS AND ADAPTED TO MEASURE THE MAGNITUDE OF SAID OUTPUT SIGNAL ENERGY TO PROVIDE AN INDICATION OF THE MAGNITUDE OF ANY EXTERNAL SIGNAL APPLIED TO SAID INPUT; AND, PROTECTIVE MEANS CONNECTED TO SAID FEEDBACK MEANS AND ADAPTED TO LIMIT POSITIVE EXCURSIONS OF THE NEGATIVE FEEDBACK SIGNAL FROM SAID NEGATIVE FEEDBACK MEANS AT LEAST DURING A TRANSIENT INTERVAL AFTER SAID CIRCUIT IS DE-ENERGIZED.