Patent GB-1115872-A (GB)
Title: Signal discriminator
IPC: H03K5/26
Filed: 1965-08-19
Abstract: 1115872 Counter input circuit HEWLETT-PACKARD CO 19 Aug 1965 [16 Sept 1964] 35708/65 Headings G4D D6Y D6C2 and D1D9G [Also in Divisions G1 and H3] In a signal discriminator circuit, for determining which of two separate inputs arrives first or for giving an output if the two inputs arrive within a given time, application of the input signals in one time relationship causes the circuit to change from a first one of three states, in which regeneration is suppressed, to a second state and application of the input signals in another time relationship causes the circuit to assume the third state. As shown, transistors 12, 14 are initially biased both ON or OFF. The first input pulse 82 or 86 causes an output from monostable circuit 74 or 78 to pass through OR gate 56 and restore regeneration between the transistors 12, 14 so that the leading edge of the first pulse after differentiating by 76, 68, 72 or 80, 66, 70, causes transistor 14 or 12 to switch to one of the other two states OFF-ON, ON-OFF for inputs occurring at A and B first respectively. The pulse occurring second does not effect the state of the circuit  selected by the first pulse but provided it occurs before the end of the first pulse, retains the regeneration until it ends when the circuit switches back to its initial condition. The output is stored by a bi-stable circuit 54 which indicates which pulse has occurred first. A low-pass filter 94 and meter 96 may be connected to the output of the bi-stable circuit. The meter indicates a + or - full-scale deflection depending on which pulse input occurred first or the reading will correspond to the time interval between the input pulses A and B if the pulses occur close together. To avoid error when the pulses occur very close together the output from the circuit may be fed back via switch S3 to control the three state circuit. If switch S1 is changed, then the circuit gives an output indication if the inputs are received within a given time. The circuit is biased so that inputs at B always render transistor 12 NON-conducting and transistor 14 conducting. If a pulse is applied to terminal A within a selected time interval it will override the bias applied to the base 48 of the transistor 14 and set the multi-vibrator to the second active state with transistor 14 ON and transistor 12 OFF In an alternative circuit Fig. 2 (not shown), for determining which of two input pulses occurs first, the first input pulse at A or B passes via OR gate (100) to a monostable circuit (102) which emits a pulse to restore regeneration within the multivibrator (106) and enable the input signal at A or B to change the state of the three state multivibrator (106), to one of the other two states. The outputs (at A, B) are fed back to disable AND gates (108, 110) so that further input pulses at A or B do not'effect the state of the multi-vibrator (106) until the end of the pulse from monostable circuit (102). The monostable circuit (102) may be switched out by a switch (S5) in which case the multi-vibrator (106) remains in its active state in which the regeneration is restored by connection from the output via D.C. inverting amplifiers (112, 120) and a further OR gate (116). This makes the states of the multi-vibrator (106) stable and the circuit can then be reset by additional inputs (at 126, 128).