Circuit for improving the signal-to-noise ratio of photoelectric devices

Claim 1

IN A CIRCUIT OF A TYPE INCLUDING A PHOTODIODE ADAPTED TO CHANGE RESISTANCE TO EFFECT CURRENT SIGNALS IN ACCORDANCE WITH AN APPLIED LIGHT SIGNAL AND TO CUT OFF THE CURRENT SIGNALS AT A PREDETERMINED FREQUENCY OF THE APPLIED LIGHT SIGNAL, A SOURCE OF POTENTIAL CONNECTED TO THE DIODE FOR PROVIDING THE CURRENT SIGNALS IN ACCORDANCE WITH THE RESISTANCE OF THE PHOTODIODE, A TRANSISTOR HAVING A BASE, AN EMITTER AND A COLLECTOR, MEANS TO CONNECT THE BASE TO THE DIODE FOR RECEIVING THE CURRENT SIGNALS, FIRST MEANS TO CONNECT THE EMITTER AND THE COLLECTOR ACROSS THE SOURCE OF POTENTIAL, AND SAID FIRST MEANS INCLUDING A RESISTOR PROVIDING AN OUTPUT IMPEDANCE; THE IMPROVEMENT COMPRISING SECOND MEANS INCLUDING A RESISTOR CONNECTED BETWEEN THE BASE AND THE SOURCE OF POTENTIAL AND ACROSS THE PHOTODIODE TO SO CONTROL AN INPUT IMPEDANCE TO THE TRANSISTOR AS TO REDUCE RANDOM FLUCTUATIONS IN THE CURRENT SIGNALS, AND THE SECOND MEANS BEING SO ARRANGED IN THE CIRCUIT IN RELATION TO SAID FIRST MEANS AS TO CAUSE THE CIRCUIT TO PROVIDE USABLE OUTPUT CURRENT SIGNALS OVER A FREQUENCY RANGE OF THE APPLIED LIGHT SIGNAL GREATER THAN THAT OF THE PREDETERMINED CUT OFF FREQUENCY OF THE PHOTODIODE.