Patent GB-1416931-A (GB)
Title: Astable or monostable circuit
IPC: G04F5/10
Filed: 1973-01-02
Abstract: 1416931 Astable and monostable circuits RCA CORPORATION 2 Jan 1973 [5 Jan 1972] 152/73 Heading H3T In a circuit selectively operable either in the astable mode or in the monostable mode, including a bi-stable circuit 50 having a first plurality of signal input terminals for producing a control signal as its output terminal in response to certain input signal conditions applied thereto and a control logic circuit, FF1, 16, having a second plurality of signal input terminals and having its output terminal connected to one of the input terminals of the bistable circuit, a gated oscillator 101 is enabled by the control signal, and a binary circuit FF4 having bi-stable states and driven by the oscillator 101 provides a feedback signal 38 to 'both the. control logic circuit FF1, 16 and to a further input terminal S of the bi-stable circuit 50 when the binary circuit is operating in a given one of its bi-stable states and the feedback signal is operable to disable the oscillator. As shown, when the inputs 10-13 are such that the output of an inverter 19 is low a P MOST 20 conducts and functions together with a NAND gate 24 to inhibit operation of the oscillator 101 which may be an integrated circuit preferably using COS/MOS devices. Astable operation.-An appropriate input to 10 or 11 causes via NOR gate 17 the output of the inverter 19 to go high so as to turn off the MOST 20 and enable NAND gate 24 so as to enable the oscillator 101, formed by inverters 22, 23, 25 and 26, to generate oscillations of frequency F determined by RC time constant elements 27, 28. An output at this frequency F is obtained at 40 and a frequency F/2 divided by a bi-stable flip-flop FF4 is obtained at 42 as long as the input is applied to input 10 or 11. Monostable operation.-By applying an input pulse to 12 or 13 an output from a NOR gate 16 is fed via NOR gate 17 and inverter 19 to start the oscillator 101. An output from the oscillator at 105 is fed to the clock inputs of bistable flip-flop FF4 and the change in its output Q4 causes via feed-back connection 38 a latch circuit 50 formed by NOR gates 17 and 18 to hold the oscillator 101 in a generating state. When the oscillator has completed one cycle as determined by RC elements 27, 28 the change in output Q4 of the bi-stable flip-flop FF4 causes via the feedback connection 38 a change in state of bi-stable flip-flop 50 to end the enable pulse from the inverter 19 so as to disable the oscillator 101 and this provides monostable operation. Pulse lengthening and a predetermined number pulse generation operation are obtained at outputs 42 and 40 by applying a retriggering input at 41 which may be obtained by a connection from input 12 or 13. A retriggering section including bi-stable flip-flops FF2 and FF3 and a NAND gate 32 function to cause an output  signal to remain at 42 in a prescribed condition until no further retriggering signal at 41 occurs. The time period of operation can be further increased by feeding the output at 42 into a counter (2, Fig. 7, not shown) such as a COS/ MOS decade counter having a reset input connected to coupled inputs 12 and 41 and an output connected to the ASTABLE input 11 to provide a further lengthened pulse (TNEW).