Patent GB-1102455-A (GB)
Title: Envelope transfer network for amplitude modulated signals
IPC: G05D3/14
Filed: 1966-04-27
Abstract: 1,102,455. Transfer function circuit. SOCIETE NOUVELLE D'ELECTRONIQUE ET DE LA RADIO-INDUSTRIE. 27 April, 1966 [30 April, 1965], No. 18439/66. Heading G4G. An envelope transfer network having a transfer function receives an amplitude modulated alternating signal of carrier frequency f and imposes upon the modulating signal a prescribed rate of attenuation and a negative phase-shift between a lower and a higher frequency value of the carrier signal, so that such characteristics appear in the envelope of the modulated signal at the network output; the network comprising a series resistance between input and output of value R<SP>1</SP>, a shunt impedance across the output comprising two equal capacitors of value C having a resistance of value R in series with each, and switching means operating synchronously with the carrier frequency to alternately connect each capacitor in the shunt branch and to simultaneously disconnect the other. The network is insertable in the control or feedback paths of a servo system responsive to an A.C. carrier, amplitude modulated by a control signal, for stabilization; and a mathematical analysis is given which shows that the network operates upon the amplitude-modulated signal similarly to a known circuit comprising a series resistance between input and output, and resistance in series with a capacitance across the output, upon an unmodulated variable input signal controlling a servo system. The network may comprise (Fig. 5) a modulated input signal e i  at 1, 2 between earth and a series resistance of value R<SP>1</SP> connected to an output terminal 4, developing a modulated voltage e 0  to earth; the terminal being connected over equal opposed diodes 121A, 122A; 121B, 122B; and equal series resistances 81A, 82A; 81B, 82B, respectively, of value 2R to the ends of symmetrical secondaries 142A, 142B of a transformer 140 having primaries 141A, 141B series energized from a reference carrier voltage e R ; the centre points of the secondaries being earthed over equal capacitors 10A, 10B of value C and the diodes being driven to perform the capacitor switching operation in synchronism with the carrier frequency of the input signal e i  (Figs. 5A, 5B, not shown). The network may be interposed between low output impedance and high input impedance transistorized matching stages (Fig. 8, not shown) and a phase lead may be introduced instead of a phase lag by emitter coupling the network to a transistor amplifier to energize an output resistor, while a further equal output resistor is energized by direct collector coupling to the transistor amplifier; the output voltage being obtained between earth and the junction of the output resistors (Fig. 9, not shown). A digitally switched network (Fig. 10, not shown) comprises a series resistance between output and input, a shunt across the output comprising two series circuits of resistances, capacitances, and coincidence gating circuits, and a bistable trigger circuit pulsed from a reference source synchronous with the carrier frequency to alternately open and close the gates. Diode, transistor or electromechanical switching may be used.