Data transmission system

In a digital data transmission system including a transmitter for phase modulated transmission of digital data over voice grade communication links without the necessity of a carrier signal and a receiver at another end of said link for recovering the data, said system comprising:

• a. a transmitter comprising:
• 1. input-clocking means for combining an input data source in binary format with a series of clock pulses and where the clock pulses are based on one-half time intervals with respect to the bit rate of the input data,
• 2. pulse train generation means for receiving the combined data source and clock pulses, said pulse training generating means comprised of an exclusive OR gate for generating an output where the output pulses have widths which are a function of the bits in the binary data,
• 3. and a bistable dividing circuit comprised of a first bistable flip-flop operatively connected to said pulse train generation means to divide the number of output pulses in said output of said exclusive OR gate to a lesser number of pulses, said lesser number of pulses being directly related to the pulses in said output but which are also bandwidth constrained in order to divide the spectral bandwidth occupied by said output,
• 4. signal generating means operatively associated with said dividing circuit to receive the output thereof to thereby generate a two level phase modulation sinusoidal varying signal for transmission over the communication link, and which signal is comprised of frequencies which lie between approximately one-fourth and one-half the wavelength of the data bit rate and where the frequencies are phase related to the data and previous phase state and with data information contained in a time interval between zero crossings of the sinusoidal varying frequency signal,
• b. and a receiver comprising:
• 1. demodulating means operatively connected to said signal generating means to receive the sinusoidal varying signal and separate the clock pulses from the binary data, said demodulating means comprising a second bistable flip-flop to divide the frequency signal at a rate of one-half of the clock pulse frequency.

A method for phase modulated transmission of data in binary format over voice grade communication links, without the necessity of a carrier signal, said method comprising:

• a. combining input data in digital binary format with clock pulses based on one-half time intervals with respect to the bit rate of the input data,
• b. generating an output pulse train in encoded waveform where the pulses in said train have widths which are a fractional function of the bits in the binary data and are bandwidth constrained,
• c. dividing the spectral bandwidth occupied by a phase transmission in a dividing circuit comprised of a first bistable flip-flop to reduce the number of pulses in said output pulse train to a number of pulses in proportional relationship therewith, but which have greater bandwidth and which are bandwidth constrained in order to reduce the frequency spectrum occupied by a phase transmission,
• d. generating a phase modulated sinusoidal varying frequency signal from said divided spectral bandwidth of the pulse train, and which sinusoidal varying signal lies between one-fourth and one-half of the bit rate of the data and where the frequencies are phase related to the data and a previous phase state, and where the data information is contained in a time interval between two successive zero crossings of the sinusoidal varying signal,
• e. transmitting said sinusoidal varying frequency signal over said communication link,
• f. demodulating said signal and separating said binary data from said clock pulses through a second bistable flip-flop to divide the frequency signal at a rate of one-half of the clock pulse frequency, and
• g. recovering the separated binary data.

A receiver circuit for use in modulator-demodulator devices which transmit and receive data with respect to information communication links, said circuit comprising:

• a. input means to receive a phase modulated sinusoidal varying frequency signal containing information representing both binary data and clock pulses and which signal lies between one-fourth and one-half of the bit rate of the data,
• b. polarity detection means operatively connected to said input means to determine the polarity of certain portions of the signal existing between selected zero crossings thereof and generating a digital pulse train where the pulses of said pulse train have widths which are a function of the binary data,
• c. differential phase detection means including at least one first bistable device operatively connected to the output of said polarity detection means to measure the instantaneous time change of phase of the frequencies and compare same to a recovered phase reference based on a previous phase change and to thereby generate a serial clock output,
• d. and at least one second bistable device operatively connected to the output of said differential phase detection means to generate a binary data output.

A modulator for phase modulated digital data transmission over information communication links without the necessity of a carrier signal, said modulator comprising:

• a. input means for receiving input data in digital binary format,
• b. clocking means for generating a series of clock pulses based on one-half time intervals with respect to the bit rate of the input data,
• c. an exclusive OR gating means operatively connected to said input means and said clocking means to receive the data and clock pulses and generate an output pulse train in encoded waveform and where the pulses in said train have widths which are a function of the binary data and are bandwidth constrained,
• d. a bistable dividing flip-flop operatively connected to an output of said exclusive OR gating means to reduce the number of pulses in said output train to a lesser number of pulses, said lesser number of pulses being directly related to the pulses in said output pulse train but which have greater bandwidth and which are also bandwidth constrained to reduce the frequency spectrum occupied by a phase transmission, and
• e. signal generating means operatively associated with said dividing flip-flop to receive the output thereof to thereby provide a two level phase modulated sinusoidal varying frequency signal which lies between one-fourth and one-half of the bit rate of the data and where the phase is related to the data and a previous phase state and with data information contained in a time interval between zero crossings of the sinusoidal varying signal.