GB1058742A - An electrical code modulation system - Google Patents

Abstract

1,058,742. Selective signalling. HITACHI SEISAKUSHO KABUSHIKI KAISHA. Mareh 17, 1964 [March 18, 1963], No. 11270/64. Heading G4H. [Also in Division H3] In a pulse code communication system pulses are transmitted continuously their density corresponding to the amplitude of the encoded signal. Encoding is effected by examining the integral of the input signal. Each time it exceeds a reference level an output pulse is produced and, at the same time, a reference potential is subtracted from the input signal. The comparison is effected by a tunnel diode, the reference level being inherent in its characteristic. Thus, Fig. 1(a), the integral of an input signal 11 is applied to a tunnel diode ED to which alternately positive and negative sampling pulses (31) (Fig. 3, not shown) are also applied (13). Normally the diode is in its high current condition 24, Fig. 2. As the output (33) (Fig. 3, not shown), of the integrator rises there comes a time when the application of a positive sampling pulse causes the diode to switch to its low current condition. This causes a fall in potential across its cathode load, and hence an output pulse 14, and also drives the input to the integrator negative via the feedback loop R 12 . The result is that while the diode is in its low current condition the integrator output falls. However, the circuit is so arranged that the next negative sampling pulse (31) always switches the diode back to its high current state, whereupon the integrator output begins to rise again, the rate of rise depending upon the magnitude of the input signal. Thus a train of output pulses can be obtained from terminal 14, each one of which corresponds to one of the positive sampling pulses, and the density of which corresponds to the magnitude of the input signal. A detailed circuit is described (Fig. 4, not shown) using mesa transistors and a Miller integrator.