Patent GB-777832-A (GB)
Title: Improvements in or relating to multiplier devices for analogue computers and the like
Inventor: DAVIS CHARLES HOWARD
IPC: G06G7/161
Filed: 1954-04-06
Abstract: 777,832. Electric analogue calculating systems. BRISTOL AIRCRAFT, Ltd. March 14, 1955 [April 6, 1954], No. 10105/54. Class 37. A multiplying device comprises means producing an alternating waveform linearly rising and falling in the respect to time, of amplitude not less than the amplitude range of a first input voltage representing the multiplicand, and passing through zero at equal time intervals ; means for changing over an electronic device between its conducting and non-conducting conditions every time the waveform passes through the amplitude valve of the first input voltage to define the time durations of the successive excursions of a constant frequency rectangular waveform so that the ratio of the difference to the sum of durations of successive excursions is proportional in magnitude and sign to the first input voltage ; means for adjusting the amplitudes and signs of the successive excursions in proportion to a second input voltage representing the multiplier; and means for continuously determining the mean amplitude of the resultant waveform, which is proportional to the product in amplitude and sign. In Fig. 1, triodes VIA, V1B are connected in a " flip-flop " circuit with a common cathode resistance which operates with the valves alternately conducting and non-conducting to generate a square waveform 22 of frequency e.g. 5 kc/s. (Fig. 2) whose half-cycles are of equal and opposite amplitudes controlled by diodes V4A, V4B whose anodes and cathodes respectively are connected to the anode of V1A and whose remaining electrodes are biased across resistance R20 of a potentiometer R19, R20, R21 across the H.T. supply. The durations of the alternate square-wave. pulses are equal, and the anode of V1B is directly coupled through potentiometer P1 and pentode amplifier V2 to the grid of cathode follower pentode amplifier V3, whose cathode is retractively coupled through capacitance C3 to the grid of pentode V2 having its anode directly coupled over resistance R8 to the grid of triode V1B, whereby an isosceles triangular voltage waveform 25 of period equal to that of the squarewaveform and adjustable for symmetry by potentiometer P1 appears on the anode of V2 and on the cathode of V3, whose control grid/ cathode voltage variations due to heater voltage changes are compensated by corresponding variationsi n the contact potential of diode V5 in the biasing potentiometer R16, R17, R18. The cathode of V3 is directly connected to the grid of triode V6A which is connected in a symmetrical resistance coupled common cathode resistance gate circuit with triode V6B, whose grid is connected over terminal 11 to a variable direct voltage 28 (Fig. 2) of magnitude klly where y is a variable factor of the multiplication ; triode V6A conducting only when waveform 25 is more positive than voltage klly to develop at the anodes of V6A, V6B a pair of antiphased square-waveforms 29, 33 such that the ratio of the difference to the sum of the durations t1 and t2 of the opposite excursions is proportional to y. The respective waveforms are directly coupled over resistances R26, R30 to squaring triode amplifiers V7A, V7B having a common cathode resistance and symmetry adjusting biasing potentiometer P3, whose antiphased outputs are respectively resistance coupled to the anodes of linear diodes V9A, V9B and to the grids of triodes V10A, V10B connected as a common load cathode follower. The cathodes of diodes V9A, V9B are respectively connected directly to the cathodes of cathode follower triodes VSA, V8B ; the grid of V8A being supplied over terminal 12 with a variable direct voltage of magnitude k<SP>1</SP>x where x is the remaining factor of the multiplication. On the grid of V10A there appears a square-waveform 34 derived from the amplified waveform 33 from V7A which is positively clipped by diode V9A so that the amplitude of each positive excursion 36 is increased proportionally to k<SP>1</SP>x above a datum level 37 corresponding to x=o when x is positive, and is correspondingly decreased below such datum when x is negative, while on the grid of V10B there appears a square waveform 35 derived from the amplified waveform 34 from V7B, which is positively clipped by diode V9B so that the amplitude of each positive excursion is decreased proportionally to k<SP>1</SP>x below the datum 37 and is correspondingly increased above datum when x is negative ; the output developed across potentiometer P4 in series with resistances R36, R41 connected between the cathodes of V8A, V8B being tapped off and phase reversed in direct connected double triode amplifier V12A, V12B followed by pentode amplifier V11 to develop on the grid of V8A a voltage of magnitude equal and sign opposite to the voltage on terminal 12. An output square waveform 39 (or 39a) appears across the common load of triodes V10A, V10B in which.the ratio is proportional to and of sign corresponding to y, and in which opposite excursions 41, 42 about reference level 40 have equal amplitudes proportional to x and corresponding in sign thereto ; this output being coupled over low pass filter comprising inductances L1, L2, L3 and capacitances C10, C11, C12, C13, resistance R54, and gain adjusting potentiometer P6 to a scaling double triode drift compensated amplifier V13A, V13B followed by pentode amplifier V14 and cathode follower V15 energizing a measuring instrument indicating the mean value of the output square wave voltage, which as shown is proportional to the product xy. In a modification, the y input voltage may be balance amplified and applied to the respective control grids of a 2-valve multivibrator to control directly the respective durations of the opposed excursions of the square-wave train generated thereby.