GB901985A - Improvements in or relating to electrical signal translating apparatus - Google Patents

Abstract

901,985. Pulse modulation circuits. AUTOMATIC TELEPHONE & ELECTRIC CO. Ltd. May 17, 1961 [May 27, 1960], No. 18781/60. Class 40 (5). In a circuit for converting input signals of variable durations into output signals of corresponding amplitudes, an amplifier connected as a Miller integrator includes a transfluxor which is controlled so that the beginning of an input signal initiates the linear change in the output voltage of the integrator and the end of the input signal terminates the linear change, the remanence of the transfluxor enabling the steady state amplitude of the output signal to be maintained at substantially the value reached on the termination of the linear change. As shown, a D.C. amplifier TX2, TX3 is connected as a Miller circuit with a feed-back capacitor CM which controls the input stage of the amplifier, transistor TX4. Before each conversion the circuit is reset by a negative-going pulse A, Fig. 2, applied at RL via a normally cut-off transistor TX 1 which energizes a reset winding W1 on a transfluxor TR to saturate the core in the direction B. A small flux in the direction A is provided by a bias winding W2 via resistors R5, R6 and is arranged to be sufficient to bring the transfluxor just out of saturation so that a small transfer of energy may take place between the windings W3, W4 supplied from an A.C. source CL. The alternating current has a frequency several orders higher than the repetition frequency of the input signal applied at IL. The output from winding W4 is rectified at D1 to D4, thus supplying a small negative potential, smoothed by C2, to the base of transistor TX2, causing it to conduct slightly and supply a positive output which keeps transistor TX3 just out of saturation. The component values are such that TX3 operates within the linear part of its characteristic and the voltage variation of its emitter provides the output signal OL. With no output the lead IL is positive and diode D5 conducts, thus preventing any change in the charge of CM. With an input signal on IL, waveform B, diode D5 is backed off and CM starts to charge, causing transistor, TX4 to be switched on and supply an increased current to winding W2 and cause an increased transformer action between windings W3 and W4, waveform CA. The increased negative potential waveform CB, causes transistor TX2 to conduct more heavily and this causes the conductivity of transistor TX3 to be reduced, causing the output voltage to go positive, waveform D, and increase the charge on CM. The output continues to increase linearly until the input signal ceases and lead IL reverts to its positive value, and the remanence of the transfluxor ensures that the output signal D remains substantially at its steady state value until the next re-set pulse is applied at RL.