Tape reader with input clipping circuit including photosensitive means

Claim 1

IN A SIGNAL EXAMINING AND INDICATING SYSTEM FOR RECEIVING INPUT SIGNALS VARYING BETWEEN A REFERENCE LEVEL AND A SECOND LEVEL TO DENOTE INFORMATION CONTENT, CERTAIN OF SAID INPUT SIGNALS BEING SUBJECT TO AN UNDESIRED ABERRATION IN THE REFERENCE LEVEL SIGNAL WHICH OCCURS ABOVE A GIVEN AMPLITUDE LEVEL AND SAID SYSTEM FURTHER BEING SUBJECT TO ENVIRONMENTAL AND OTHER NOISE ALSO OCCURRING ABOVE SAID GIVEN AMPLITUDE LEVEL, THE IMPROVEMENT WHICH COMPRISES A CLIPPING CIRCUIT COMPRISING A SERIES CIRCUIT COUPLED BETWEEN TWO DIFFERENT PLANES OF SUPPLY POTENTIAL, SAID SERIES CIRCUIT COMPRISING A FIRST IMPEDANCE, A SECOND IMPEDANCE, A PHOTOSENSITIVE SEMICONDUCTOR UNIT, A THIRD IMPEDANCE, AND A FOURTH IMPEDANCE, SAID CLIPPING CIRCUIT PASSING A CONTROL SIGNAL RESPONSIVE TO A VARIATION OF SAID INPUT SIGNAL BELOW SAID GIVEN AMPLITUDE LEVEL, A DIFFERENCE AMPLIFIER INCLUDING AT LEAST TWO INPUT CONNECTIONS AND ONE OUTPUT CONNECTION, MEANS FOR COUPLING THE JUNCTION OF SAID FIRST AND SECOND IMPEDANCES TO ONE INPUT CONNECTION OF SAID DIFFERENCE AMPLIFIER, MEANS FOR COUPLING THE JUNCTION OF SAID THIRD AND FOURTH IMPEDANCES TO THE OTHER OF SAID INPUT CONNECTIONS OF SAID DIFFERENCE AMPLIFIER, A DIFFERENCE DETECTOR CIRCUIT FOR RECEIVING THE CONTROL SIGNAL FROM THE DIFFERENCE AMPLIFIER WHENEVER THE VARIATION OF INPUT SIGNAL INDICATES RECEIPT OF AN INPUT SIGNAL WITH A VARIATION OF INFORMATION CONTENT, AND MEANS FEOR COUPLING SAID OUTPUT CONNECTION OF THE DIFFERENCE AMPLIFIER WITH SAID DIFFERENCE DETECTOR CIRCUIT TO PROVIDE A POSITIVE INDICATIONOF RECEIPT OF INFORMATION-DENOTING SIGNALS IN SAID SYSTEM.