Patent GB-1092512-A (GB)
Title: Improvements in or relating to electrical signal smoothing circuits
Inventor: UDALL ANTHONY JOHN SHAWCROSS
IPC: H03K3/2893
Filed: 1963-08-13
Abstract: 1,092,512. Pulse generators. ELECTRIC & MUSICAL INDUSTRIES Ltd. Aug. 4, 1964 [Aug. 13, 1963], No. 32021/63. Heading H3P. [Also in Divisions G4 and H2] In a time division multiplier circuit, an input terminal 1 receiving analogue voltage x and terminal 4 receiving a voltage + k are connected over equal resistors 2, 5 to input of amplifier 3 while terminal 6 receiving a voltage - k is is connected over resistor 7 (half the value of resistors 2, 5) and switch 8 to the amplifier input, whose output is connected to trigger circuit 9 and over opposed diodes 10, 11 to voltage - k on terminal 12; the diode cathode junction being returned to - 300 volt line 14 over resistor 13 and over opposed diodes 15, 17 to voltage +k in terminal 18, while the diode anode junction is connected over resistor 19 to +300 volt line 20. Trigger 9 controls switch 24, receiving an input analogue voltage - y over resistor 23 and supplying its output to feedback amplifier 25, also receiving analogue voltage +y over resistance 26 (which is twice the value of 23). The amplifier output is connected over equal resistors 29, 30 to points A and B also connected over equal resistors 32, 33 to the output of rectifier bridge 31 energized from terminals 21, 22 with analogue voltages Œy. Points A, B are connected over rectifiers 34, 35 to feedback amplifier 36. The output is back connected to A, B over equal resistors 38, 39 and also amplified at 40 for connection to output terminal 42, and also over resistor 41 (equal to 26) to the input of amplifier 25. In operation, switch 8 is initially non- conductive, trigger 9 is in the 0 state, the output of 3 is more negative than +k, and diodes 10, 15 conduct so that condenser 16 provides feedback for 3. The output voltage falls linearly in proportion to (x + k) to value - k, when diode 10 becomes non-conducting to disconnect condenser 16, and the output voltage falls rapidly to the amplifier negative saturation voltage. Trigger 9 arranged to change to 1 state at - k and to 0 state at +k changes over to 1 state, and input current to 5 is proportional to (x + k - 2h) = (x - k). Since k > x the output voltage rises to - k, diode 10 conducts, and the voltage rises linearly in proportion to (x - k) to +k, when diode 15 becomes non-conducting to disconnect condenser 15, when the cycle recommences, so that rectangular waves of duty cycle x - are generated, and valve k is variable to give k division. Gate 24 opens when trigger 9 is in 1 state, so that the input current to amplifier 25 from terminals 21, 22 is a rectangular waveform of excursion defined by Œxy and average current value xy/k. Assuming voltage at terminal xy 42 is - the average total current to the input k of 25 is zero for static input, and the output waveform of 25 is a combined step and ramp alternately symmetrical about zero. Rectifier 31 produces output voltages of +y and - y, and terminals A, B are limited to negative and positive potentials of xy/k respectively under   static conditions with voltage -xy/k on con-   denser 37 and xy/k at terminal 42. If x becomes more positive, the positive going ramp in the output of 25 lengthens and the negative going ramp shortens, so that B goes positive for a small part of the waveform, and diode 35 conducts to amplifier 36 a positive signal, so that the voltage across feedback capacitor 37 increases negatively and the output voltage at terminal 42 becomes more positive, while the zero total average current input to amplifier 25 is restored to zero by feedback over resistor 41. Changes in value of y also vary the size of the steps and slopes of the ramp in the output waveform of amplifier 25, which ultimately changes the voltage on condenser 37 and restores the zero total average input current to amplifier 25. The changes also vary the bias of points A, B relative to the input of amplifier 36, so as to vary the " dead space " generated by the Œy biases derived from bridge 31 in conjunction with diodes 34, 35; the " dead space " being maintained equal to the amplitude of the output ripple waveform of amplifier 25 by its dependence on y. Resistor 27 stabilizes the loop including amplifiers 25, 36, 40 and resistor 41, and introduces a proportion of the rectangular waveform at the input of amplifier 25 into the output waveform thereof, so as to accelerate the response of condenser to variations of y. The multiplying circuit shown in the Provisional Specification differs in detail.