Patent GB-817901-A (GB)
Title: Electronic switches and analogue computers incorporating the same
IPC: H03K17/74
Filed: 1956-04-06
Abstract: 817,901. Electric analogue calculating systems. SOC. D'ELECTRONIQUE ET D'AUTOMATISME. April 6, 1956 [April 7, 1955], No. 10592/56. Class 37. [Also in Group XL (c)] Fig. 1 shows a time division analogue multiplier computing circuit wherein an input X voltage is applied over resistor 3 (of value R) to amplifier 2 having time integrating feedback over condenser 4 (of value C). A rectangular reference voltage waveform is also applied to the amplifier input over resistor 5, and the combined integrated output is applied to control a " flipflop circuit 7. As the integrated voltage reaches predetermined value Œ K the flip-flop circuit changes over and its output 8 alternately unblocks the opposed and normally non-conductive diodes 9, 10 according as the output voltage is at its higher or lower value, to derive a reference voltage waveform Œ E applied to the amplifier over resistor 5 (of value 2R). The output voltage from 2 is represented by an asymmetrical sawtooth waveform whose rise and fall times are respectively A further output 11 of the flip-flop circuit 7 drives a cathode follower 12 conducting or non- conducting on adjacent excursions to generate a rectangular waveform C at 14 (Fig. 4, not shown) whose alternate excursions have durations T 1  and T 2  and whose average value is proportional to X. A phase inverter 15 develops a complementary waveform C which together with C is applied to control an electronic switch, wherein amplifier 32 having negative feedback over resistor 33 (of value 2R) receives waveform C R over resistor 29 (of value -) and complementary 2 input signals Œ Y over series attenuating resis- R tors 24, 25 and 27, 28 (each of value -). The 2 anode of diode 31 is connected to the junction of resistors 27, 28 and the cathode of diode 30 in series therewith to the junction of resistors 24, 25, while the interconnection receives waveform C. Over a time interval T 1  the signals C, #C are respectively at their upper and lower values so that diode 30 conducts and diode 31 is blocked, while over a time interval T 2  the reverse condition obtains. It is shown that during T 1  the input 26 of amplifier 32 receives current so that the mean current and the mean amplified output represents the product of the input variables (Fig. 4, not shown). Distortion due to the finite resistance values of the diodes by comparison with the summation resistances is shown to be eliminated by applying the complementary signal #C to resistor 29 of value R/2 from a potentiometer comprising reversedly connected diodes 35, 36 R and earthed resistor 39 (Fig. 2) of value -. 2 Accuracy may be further increased by splitting resistors 24, 27 into halves 24<SP>1</SP>, 24<SP>2</SP> and 271, 272 and connecting further diodes 37, 38 in series between the centre points; the cathode anode junction being connected to the source of signal C '(Fig. 3) and the cathode anode junction of diodes 30, 31, while the signal C is connected direct through diodes 35, 36 with the elimination of resistor 39. The electronic switching circuit may be further modified by duplicating the circuit comprising the series diodes 30, 31 and resistors 24, 25, 27, 28, using series diodes 40, 41 of opposite polarity together with corresponding resistors 44, 45, 47, 48 (Fig. 5). Signals representing Œ Y are respectively applied to terminals 22, 23, 42, 43 while complementary control signals C, are applied to the appropriate anodes and cathodes of the diodes over variable resistors 49, 50, 51, 52 for equalization of the resistances of the several diode paths; the required product voltages being obtained from amplifier 32 as before, excited from the common point of resistors 25, 28, 45, 48. To reduce errors due to variations of diode internal resistances with different current values therein due to variations of Y, shunt resistances are respectively connected between the outputs of the opposite pairs of series diodes to pass constant currents proportionate to signals C and #C which traverse the diodes and reduce the current variation with the Œ Y voltages; the opposite sides of the two circuits being connected to the ends of a balancing potentiometer to whose slider the output amplifier is connected (Fig. 6, not shown).