Method and apparatus for demodulation of phase difference modulated data signals

Claim 2

Apparatus for demodulating phase difference modulated carrier signals wherein the carrier is modulated by specific, different valued phase shifts, said phase shift values corresponding to the various levels of a data signal, said phase shifts succeeding one another in a predetermined modulation interval, comprising: reference oscillator means for generating a rectangular oscillation signal having a frequency of a value equal to n times the carrier frequency, where n equals the number of phase values with which said carrier signal is modulated, frequency divider means for reducing said reference oscillator output frequency to said carrier frequency, means for receiving said modulated carrier, limiter means for changing said modulated carrier waveform to a rectangular waveform, gate means, the outputs of said limiter means and said frequency divider means being connected to inputs of said means, timing generator means connected to said gate means for opening said gate means for a predetermined interval to allow a portion of said carrier waveform pass through said gate, and synchronizing circuit means having said portion of said limited carrier waveform and said reference oscillator output applied thereto for comparing the latter two signals, and including means responsive to the result of said comparison for correcting said reference oscillator output signal by a phase value of an amount corresponding to the time deviation between said two compared signals.

Claim 3

The apparatus defined in claim 1 wherein said reference oscillator means comprises a series connection of a frequency generator, said synchronizing circuit means and a second frequency divider means which emits n times the carrier frequency at the output thereof, the output of said second frequency divider means being connected, as the reference oscillator output, to said synchronizing circuit means; and wherein said synchronizing circuit means includes means for one of blocking a predetermined portion of said reference generator output from said second divider means and adding pulses to the reference generator signal applied to said second divider means depending on the result of said comparison of said carrier waveform and the divided reference generator outputs.

Claim 4

In a data transmission system wherein binary coded data are transmitted by predetermined different valued phase shifts corresponding, respectively, to combinations of binary levels which modulate a carrier signal and wherein the different valued phase shifts follow each other within a fixed time interval thereby determing a modulating interval, a method for demodulating the phase difference modulated carrier signals for deriving the transmitted binary coded data, comprising the steps of: receiving said phase difference modulated carrier signal, generating a reference frequency signal having all the phase values included in said received signal, deriving a signal from said received signal in which the phase values are contained in crossovers of the derived signal, producing a pulse when a crossover of said derived signal occurs, comparing the phase of said produced pulse with the corresponding phase of said reference frequency, correcting the phase of said reference frequency in accordance with the result of said comparing step to remove any phase error between said derived signal and said reference frequency, forming binary phase values from said reference signal, storing a said binary phase value when a crossover of said derived signal coincides with a said binary phase value, comparing said stored binary phase value with the phase position of the next succeeding crossover of said derived signal and producing a difference signal corresponding in valve to the difference between the compared phase values and decoding said difference signal to obtain said binary coded data.

Claim 5

In a data transmission system wherein binary coded data are transmitted by predetermined different valued phase shifts corresponding, respectively, to combinations of binary levels which modulate a carrier signal and wherein the different valued phase shifts follow each other within a fixed time interval thereby determing a modulating interval, a method for demodulating the phase difference modulated carrier signals for deriving the transmitted binary coded data, comprising the steps of: receiving said phase difference modulated carrier signal, generating a reference frequency signal having all the phase values included in said received signal, deriving a signal from said received signal in which the phase values are contained in crossovers of the derived signal, producing a pulse when a crossover of said derived signal occurs, comparing the phase of said produced pulse with the corresponding phase of said reference frequency, correcting the phase of said reference frequency in accordance with the result of said comparing step to remove any phase error between said derived signal and said reference frequency, forming binary phase values from said reference signal, storing a said binary phase value when a crossover of said derived signal coincides with a said binary phase value, comparing said stored binary phase value with the phase position of the next succeeding crossover of said derived signal and producing a difference signal corresponding in valve to the difference between the compared phase values and decoding said difference signal to obtain said binary coded data.

Claim 6

The method defined in claim 3 wherein said correcting step further comprises adding pulses to, or subtracting pulses from, said reference frequency, as necessary, in accordance with the result of said comparing step wherein the phase of said produced pulse is compared with the phase of said reference frequency.

Claim 7

The method defined in claim 3 wherein said correcting step further comprises shifting said reference frequency by a small constant phase value until any of said phase error between said derived signal and said reference fequency, as determined from said comparing step, is removed.