GB928090A - Improvements in or relating to logical circuits - Google Patents

Abstract

928,090. Diode gating circuits; transistor bi-stable circuits. PHILIPS ELECTRICAL INDUSTRIES Ltd. (Philips' Gloeilampenfabrieken N.V.). Sept. 28, 1959, No. 32882/59. Class 40 (6). [Also in Group XIX] A diode gating circuit which delivers an output pulse whose amplitude exceeds a predetermined value at terminal 9 when a predetermined combination of steady input potentials are applied at input terminals 2-7 and a pulse of predetermined magnitude and sign is applied at terminal 8 comprises a first set of input terminals 2, 3, 4 connected through respective similarly poled diodes to one electrode of a capacitor 10 and a second set of input terminals 5-8 connected through respective diodes poled in the same direction as those connected to terminals 2-4 to the other electrode of the capacitor, each electrode of the capacitor being connected to a point of fixed potential through respective resistors 18, 19 and the output terminal 9 being connected to one side of the capacitor through a diode 20 which as regards its connection to capacitor 10 is poled oppositely to those connected to the input terminals. In the circuit shown in Fig. 1 each of the input terminals may assume either of two potentials, i.e. earth potential and a negative potential equal to that to which the resistors 18 and 19 are connected, the potentials at the terminals 2 to 7 being constant while that at terminal 8 being capable of rapid transitions between its two possible values. When one or more of the first set of inputs 2-4 is at earth potential the corresponding electrode of capacitor 10 is at earth potential. Similarly if all of the second set of inputs 5-8 are at the negative potential the corresponding electrode of capacitor 10 will. be at that potential. Thus under these conditions when the potential at terminal 8 executes a rapid positive change to earth potential, the potential of the lower electrode of the capacitor will change likewise and its upper electrode will go positive to earth so delivering a positive pulse output at terminal 9. As shown in Fig. 2 illustrating the application of the circuit to a binary counter or frequency-halving circuit, circuit 30 is a conventional reciprocally-coupled bi-stable pair of transistors which can be triggered from one state to the other by pulses 78 applied through a diode gating circuit 60 in accordance with the invention. In this circuit terminals 62, 64 constitute one set of input terminals and terminals 63, 65 the other set. Assuming that transistor 31 is conducting and transistor 32 is cut off, in the negative-going intervals between the switching pulses 78, one of inputs 62, 64 is at earth potential (viz. input 62) while both inputs 63, 65 are negative. Hence when the next switching pulse 78 arrives a positive pulse is delivered to output terminal 66 and is applied to transistor 31 to change the state of the circuit 30. Similarly the next switching pulse causes an output to appear at terminal 67 to switch the circuit 30 back again.