GB765825A - Electrical translation system - Google Patents

Abstract

765,825. Non-linear and pulse code modulation circuits. STANDARD TELEPHONES & CABLES, Ltd. March 11, 1955 [March 29, 1954], No. 7228/55. Addition to 659,576. Classes 40(5) and 40(6) In a circuit of the type described in the parent Specification in which an input signal is applied to a non-linear circuit and the outputs combined to give the desired curve each circuit comprises a first rectifier 6 and second rectifier 5, arranged in series opposition, Fig. 1, the rectifiers being biased to present a threshhold and saturation voltage level so that the output 38 produced from the input 12 is according to the curve 14, 15, 16, Fig. 2. In the absence of an input, the bias potential E<SP>3</SP> drives current through resistors 7, 8 and rectifier 5 to battery E<SP>1</SP> to set up and threshhold voltage E<SP>2</SP> eaual to potential E<SP>1</SP> plus the potential difference across resistor 8. Until the input exceeds E<SP>2</SP>, a rectifier 6 is biased off, the output voltage then rising with input as the current through resistor 7 falls, curve 15, Fig. 2. When the input equals or exceeds E<SP>3</SP> rectifier 5 is biased off and the output remains constant, curve 16. A number of circuits are employed with differing bias sources E\ E<SP>3</SP>, Fig. 5, and the outputs added to give the curve 17 which can be employed as the compander or expander in a pulse code modulation system, Figs. 3, and 4 (not shown). Each circuit, such as 5a, 6a, 7a, 8a, Fig. 6, is biased from taps on potential divider 25 and the signal is fed out over a de-coupling resistor 35a to a common resistor 37. Adjustment of the bias from tap 29 varies.the amplitude of input volts necessary to exceed the threshold voltage. In a modification, Fig. 9, decoupling capacitors 51 are added and two of the intermediate resistors 62d, 62e are tapped on potential divider 47. Since the output of the extreme non-linear circuits are much larger than the rest, resistors 55, 57 are included to attenuate the output. Distortion of pulses due to capacity effects are overcome by the use of compensating capacitors 63. A similar circuit (Fig. 10, not shown) may be used as the expander. Where a series of characteristics such as the curves A, B and C of Fig. 8 are required in order to code an input signal, calculated fractions from the non-linear circuit are applied in one sense or the other to the primary of transformer 40, Fig. 7. A three-element codeis obtained by feeding through separate mixing circuits B 'and C and delays 43, 44 before the final addition across resistor 45. Specification 535,860 [Group XL] also is referred to.