GB686583A - Improvements in or relating to quantized signal transmission systems - Google Patents

Abstract

686,583. Pulse code modulation systems. WESTERN ELECTRIC CO., Inc. June 26, 1951 [June 29, 1950], No. 15122/51. Class 40 (v). In a communication system in which the signals are sampled and variably quantized, the size of the quantum, or difference in level between successive quantized samples, is made relatively small for signals of slowly varying amplitude and relatively large for signals of rapidly varying amplitude. The embodiment described comprises a system in which the changes of level of successive quantized signals are transmitted rather than the levels themselves. The difference 14 between the input signal 11 and the reconstituted signal 13, derived from the output of the integrator 23, is produced in the subtractor circuit 12 and fed to a level control circuit 16. The output 17 therefrom is sampled and quantized in circuit 18 producing a signal 19 which operates coder 25 feeding coded signals to the transmission path 27. The output of quantizer 18 is also passed through a second level control circuit 21 producing an effect on the quantized signal which is the inverse of that of the first control circuit 16, so that the output 22 is a quantized replica of the signal 14. Signal 22 is applied to the integrator 23 which provides a decoded version 13 of the original signal 11, for application to the subtractor 12. Signal 22 also provides a control voltage for circuits 16 and 21 after a delay in circuit 24 of one sampling period. This causes the gain of circuit 16 to depend, at any sampling instant, on the amplitude of the preceding restored sample which produces the desired quantum level control. The receiver, at the other end of transmission path 27, comprises a decoder 28 followed by level control circuit 31, controlled through delay circuit 32, and integrator 34 which correspond to the circuits 21, 24, 23, respectively, at the transmitter. Typical related waveforms of signals 11, 13, 14, 17, 19 and 22 are given, Fig. 2 (not shown) Amplifiers, with controlled feed-back paths, for use as level control circuits 16, 21, 31, are described, Figs. 3, 4 (not shown). Specification 652,212 and U.S.A. Specification 2,605,361 are referred to.