Patent GB-1117821-A (GB)
Title: Improvements in electrical signal function generators
Inventor: WARREN JOHN GEORGE
IPC: G06G7/28
Filed: 1966-02-02
Abstract: 1,117,821. Function generators. SOLARTRON ELECTRONIC GROUP Ltd. 20 Jan., 1967 [2 Feb., 1966], No. 4669/66. Heading G4G. A function generator comprises an n stage shift counter 13 having stages m 1  to m n , all but one of which are in the 0 state, while as the counter is pulsed a 1 state is shifted sequentially through the stages; each stage comprising a bi-stable circuit containing a relay energized in the 1 state, to close corresponding pairs of contacts S 1  to S n  and T 1  to T n  controlling two sets of current sources comprising resistors F 1  to F n  and T 1  to T n  with corresponding voltage sources V 1  and V 2 , so that the sources of each set are connected one by one in sequence to the input of a first quadripole network 8 and a second quadripole network 9. Network 8 comprises operational amplifier 12 with resistive feedback in tandem with switch 19, resistance 22, and operational amplifier 11 with capacitative feedback over 21, having a positive transfer function b/p, where p is the differential operator and b is determined by the values of 21 and 22. Network 9 comprises operational amplifier 16 with resistive feedback and a constant negative transfer function. Voltages V 1 , V 2  are opposed in sign, providing voltages E, H of similar sign which are developed at outputs 10, 20. Such voltages are applied to a voltage comparator 17 which at equality pulses counter 13 over differentiating capacitor 23 and unidirectional diode 24. Initially, if counter 13 is in state m 1 , switches S 1 , T 1  are closed and if switch 18 is open, steady signals D, H (Figs. 2 at time 0) are developed at points 19, 20 defined respectively by F 1 , G 1 . On closure of switch 18, signal E rises until = H at point h 1  to define segment Oh, operate comparator 17 so that counter 13 assumes state m 2 , open switches S 1 , T 1  and close switches S 2 , T 2  so that the new signals D, E, H restore 17 to its original state, so that E rises with a new slope F 2  to define segment h 1 , h 2 . The process reiterates until a curve O-h n  has been defined. The break points h 1  to h n  are defined by resistors G 1  to G n  and the segmental slopes by resistors F 1  to F n , and signals D, H approximate to - cos t, sin t, where t is time, since for integrator 11, 21 sin t = - # - cos t. The switching may be transistorized. Figs. 3, 4 (not shown) illustrate a more sophisticated circuit for generating signals representing sin, cos t over four quadrants. Fig. 5 (not shown) illustrates a modification wherein resistors F 1  to F n  are replaced by three resistors 4r, 2r, r switchably selected by a high-speed three-stage binary counter, while resistors G 1  to G n  are switchably preselected by a binary to decimal decoder. Fig. 6 (not shown) illustrates the graphical calculation of the values of resistors G 1  to G n  and Fig. 7 (not shown) illustrates the approximation of the maxima and minima of a curve to a parabola by arranging switch S n  to introduce in series with resistor F n  a further resistance in series with a capacitance feedback integrating amplifier, whereby the transfer function of network 8 over the interval h n-1  to h n+1  is the form so that there is no break point at h n , but H (Fig. 2) preserves the same value from h n-2  to h n+1 , and h n+1  is detected when E falls from H after following a parabola from h n-1