GB1102350A - Stabilising the response of a resonant filter - Google Patents

Abstract

1,102,350. Analogue-to-digital converters. STANDARD TELEPHONES & CABLES Ltd. 17 Oct., 1966, No. 46296/66. Heading G4H. In a PCM system of the kind in which successive samples are applied to shock-excite a damped tuned circuit 2, Fig. 1, the number of oscillations above a given amplitude being a measure of the sample, the damping of the tuned circuit is controlled by a temperature-sensitive resistor, the output of the tuned circuit being applied to a stable reference circuit, the output of which decays at a fixed rate, this output being compared with the output of the tuned circuit and the difference being applied to the heater of the temperature-sensitive resistor to adjust the damping so that the output also decays at the fixed rate. The output of the tuned circuit is applied to an overload amplifier which limits the amplitude of the oscillating signal (a), Fig. 5, a low-level linearizer which imposes a linear law on the output of the amplifier. Bistable 5 acts as a threshold device producing pulses which, after differentiation and rectification, pass to counter 9. The value reached is transmitted serially. The signal (a) from the overload amplifier is applied to amplifier T1, Fig. 3, and passes via clipping diodes, which reduce the direct current component, to amplifier T2, passing only the positive part of the signal (b). This is applied to the comparator T4, T5 via an emitter follower, and through a peak voltmeter T3 acting as a peak storage circuit. The output (c) passes to a second peak voltmeter D4, the delay rate of which is faster than that of the first and gives the fixed value for comparison. The output signal of D4 is applied to comparator T4, T5, the initial parts of the signal being augmented by a circuit LLBC to produce signal (h). The difference signal (f) after further processing is passed to the heater of the temperature-sensitive resistor connected in the L-C circuit of the oscillator to bring the decay rate to the standard value as given by the peak voltmeter D4.