| 摘要 |
997,715. Pulse modulation systems. KOKUSAI DENSHIN DENWA KABUSHIKI KAISHA. July 12, 1962 [Sept. 11, 1961], No. 26871/62. Heading H4L. In a system for converting a television video signal into a pulse code modulated signal, the television signal represented by So Fig. 2, is added to a signal Fo of much higher frequency which ideally is of triangular wave form but may be sinusoidal, its amplitude being equal to one quantum level. If the combined signal S c is sampled at a frequency equal to that of F 0 , and assuming a reference or threshold voltage V r defining one quantum level, duration modulated pulses S q will result each time the combined signal is greater than the reference level, but if the sampling frequency is arranged to be much higher than the frequency of F 0 , the output signal S s is in the form of pulse number modulation, i.e. the density of the pulses is proportional to the brightness. Both positive and negative sampling signals are used, Fig. 2(E), the positive sampling signal being gated when the signal to be coded is greater than, and the negative sampling signal being gated when the signal to be coded is less than the reference level. In a modification, Fig. 4 (not shown), two reference levels representing two quantum levels are indicated which produce two separate p.c.m. trains. In order to prevent interference with the video signal, the frequency of the signal F 0 may be arranged to be an odd multiple of half the horizontal scanning frequency. In a colour television system the subcarrier wave or a harmoic thereof may be used as the signal F o . |
