GB1066884A - Improvements in or relating to the analysis of signal sequences, and circuitry therefor - Google Patents

Abstract

1,066,884. Purifying signals. INTERNATIONAL BUSINESS MACHINES CORPORATION. July 13, 1964 [July 13, 1963], No. 28886/64. Heading H3T. [Also in Division G4] Signals are freed from spurious components by passing them to the inputs of a differential amplifier in one case directly and in the other case via a voltage divider, rectifier and a storage element to produce a reference voltage (Fig. 1, not shown); the subtracted output from the differential amplifier comprises the desired signal. The voltage divider may be included in the first input to the differential amplifier instead of the second (Fig. 3, not shown). The invention is useful in cleaning up the signals obtained by the optical or capacitative scanning of markings on cards. In Fig. 5, the differential amplifier comprises a Schmitt trigger circuit Tr1 and Tr2, the input signal at a being fed to the base of Tr1 via level-restoring diode D2 and to the base of Tr2 via voltage divider R1-R2, diode D1 and storage capacitor C1. Noise signals which are insufficient to cause Tr1 to conduct are passed on to Tr2, C1 charging and discharging through R4, R5 and R6, but larger noise signals turn on Tr1 making the potential at d less negative and thus increasing the effective time constant of the circuit. C1 cannot then pass on rapid fluctuations due to noise but can transmit the signals which are of longer duration. Diode D3 exerts a further levelrestoring function.