DIFFERENTIAL PHASE MODULATOR AND DEMODULATOR UTILIZING RELATIVE PHASE DIFFERENCES AT THE CENTER OF THE MODULATION PERIODS

摘要

Digital data transmission at a very high bit rate through randomly selected voice-grade telephone lines by the use of a transmitter which includes digital differential angle modulation; and a receiver which includes digital differential angle demodulation is disclosed. Binary data wherein the individual bits are represented by a discrete level format during bit cell times is stored in multibit groups of randomly varying data patterns. Each multibit group is converted from its digital level format to a predetermined phase level format which includes a plurality of different phase, or angle, increments. At the transmitter a divider circuit receives a high-frequency signal which is many times higher than the bit rate of the data to be transmitted, and divides it into an intermediate frequency square wave signal which is still many times higher than the bit rate. The predetermined phase levels representative of each multibit group are compared with divider output taps by a comparison circuit which selectively alters the dividing operation so that an information-representing phase-shifted intermediate frequency signal is emitted. This information-representing phase-shifted signal is filtered and translated down to a low-frequency analog signal which is passed through a narrow band pass communication link exhibiting a linear phase over the band pass width.