GB1339746A - Data communication apparatus - Google Patents

Abstract

1339746 Digital transmission; phase modulation MARCONI CO Ltd 4 May 1971 [4 June 1970] 26931/70 Heading H4P A differential phase modulation receiver stores, for at least the duration of each bit, voltages respectively representative of the sine and cosine of the phase angle, which voltages are combined and compared with the resultants appropriate to successive bits. Two channels are provided to which bits are switched alternately, each channel having two parallel paths, one having a first product detector producing a cosine function and the other producing a similar sine function, both having separate storing circuits feeding into a combining circuit the signal which is compared with the corresponding signal from the other channel successively. Each D.C. storing circuit may comprise a capacitor with a switch device operated at bit frequency to discharge the capacitor at the end of each storage period. An electronic switch IS diverts successive bits alternately to channels 1, 1<SP>1</SP>, each of which has two parallel paths. One path has a product detector 11, a D.C. store 13, a modulator 15 and low-pass filter 17 to which reference voltages of the forms A cos (#t+#) and B cos (#t+#) are fed, and similar sine functions are fed to the other path. The other channel is identical. The product detectors 11, 12 are shown in greater detail in Fig. 2 (not shown). Phase comparison of the outputs from 19, 19<SP>1</SP> are switched by 2S, synchronized with IS, to phase comparator 21, the output from which may be utilized in any manner known per se.