GB939308A - Improvements in or relating to circuits for providing a signal indicating the presence or the absence of clock pulses - Google Patents

Abstract

939,308. Voltage detecting. PHILIPS ELECTRICAL INDUSTRIES Ltd. Aug. 14, 1962 [Aug. 17, 1961], No. 31165/62. Class 37. [Also in Group XL (e)] A circuit for detecting the presence or absence of needle-like clock pulses comprises a bi-stable circuit FF1, the 1 input of which is fed with the monitored clock pulses, the 0 input being fed from the output of a pulse generator delivering needle-like pulses of a lower frequency and the output of the bi-stable circuit controls a gate P also fed with the lower frequency pulses, the operating delay of gate-P being greater than the duration of each lower frequency pulse. As shown, a generator X delivers square wave clock signals in phase opposition via gates Q1, Q2 to terminals 7, 8. The square waves are differentiated at 1, 2 and the resulting positive needle-like pulses from each phase are passed via diodes 4, 5 to the transistorized Eccles-Jordan bi-stable circuit FF1. A square wave from a second clock generator Y is differentiated at 3 and the positive needle-like pulses therefrom fed to the 0 input of FF1 so that the circuit is set to its 1 state by each positive pulse from X and reset by each positive pulse from Y. The operating delay of FF1 and the gate P is such that, under normal circumstances, needle-like pulses from diode 6 do not have time to pass gate P. In the event of failure of generator X, circuit FF1 will remain in its 0 state hence the next pulse through diode 6 will set the bi-stable circuit FF2 to its 0 state, closing gates Q1, Q2 and opening gates R1, R2, thereby connecting the output terminals 7, 8 to the auxiliary clock generator Y. Bi-stable circuit FF2 is reset manually by switch S2. Operation of the circuit may be checked by opening switch S1. Fig. 1 (not shown) relates to an alarm circuit in which gates Q1, Q2, R1, R2 are omitted and clock generator Y is replaced by a pulse generator having a frequency two-thirds that of the monitored clock generator.