Facsimile receiver with improved demodulator

Claim 2

A facsimile receiver for producing a copy at a receiving location in response to signals representing light-dark variations in a document at a remote transmitting location, said receiver comprising: trigger means responsive to said light-dark signals for generating trigger signals having a variable frequency representing light-dark variations in a document; timing means coupled to said trigger means for timing out periods of predetermined duration, said timing periods being initiated in response to trigger signals; reset means coupled to said trigger means and said timing means for resetting said timing means in response to trigger signals occurring during said timing periods; detector means coupled to the output of said timing means for generating a writing control signal varying as a function of the ratio of timing periods to the time between timing periods; and writing means coupled to the output of said timing means for marking on a copy medium to reproduce the light-dark variations of the document on the copy medium in response to said writing control signal.

Claim 3

The facsimile receiver of claim 1 wherein said timing means comprises a capacitor charged and discharged in response to said trigger means and said reset means.

Claim 4

The facsimile receiver of claim 2 wherein said timing means further comprises a flip-flop set in response to trigger signals, a reference voltage, a voltage comparator coupled to said reference voltage and said capacitor for comparing the reference voltage with the charge on said capacitor and automatically resetting said flip-flop when the charge on the capacitor reaches a predetermined level, and switch means coupled to said reset means for discharging said capacitor in response to each of said trigger signals, the output of said flip-flop being coupled to said detector means.

Claim 5

In a facsimile receiver for producing a copy at a receiving location in response to signals representing light-dark variations in a document at a remote transmitting location, said receiver comprising trigger means responsive to said FM signals and noise to generate trigger signals having a variable frequency proportional to the frequency of said FM signals and said noise, a single shot multivibrator coupled to the output of said trigger means for generating a multivibrator output signal having an astable state of fixed duration initiated in response to said trigger signals, the ratio of the astable state duration to stable state duration being directly proportional to the frequency of said trigger signals, detector means coupled to the output of said single shot multivibrator for generating a writing control signal representing said ratio, and writing means coupled to the output of said detector means for marking on a copy medium to reproduce said light-dark variations of said document on said copy medium in response to said writing control signal, the improvement comprising: reset means coupled to said trigger means for resetting said multivibrator and reinitiating said astable state in response to each of said trigger signals including trigger signals occurring while said multivibrator is in the astable state.

Claim 6

In a facsimile receiver for producing a copy at a receiving location in response to signals representing light-dark variations in a document at a remote transmitting location, said receiver comprising trigger means responsive to said FM signals and noise to generate trigger signals having a variable frequency proportional to the frequency of said FM signals and said noise, a single shot multivibrator coupled to the output of said trigger means for generating a multivibrator output signal having an astable state of fixed duration initiated in response to said trigger signals, the ratio of the astable state duration to stable state duration being directly proportional to the frequency of said trigger signals, detector means coupled to the output of said single shot multivibrator for generating a writing control signal representing said ratio, and writing means coupled to the output of said detector means for marking on a copy medium to reproduce said light-dark variations of said document on said copy medium in response to said writing control signal, the improvement comprising: reset means coupled to said trigger means for resetting said multivibrator and reinitiating said astable state in response to each of said trigger signals including trigger signals occurring while said multivibrator is in the astable state.

Claim 7

The facsimile receiver of claim 4 wherein said multivibrator comprises a capacitor, a flip-floP coupled to said capacitor, a reference voltage, a voltage comparator coupled to said reference voltage and said capacitor for comparing the reference voltage with the charge on said capacitor and automatically resetting said flip-flop when the charge on the capacitor reaches a predetermined level and switch means coupled to said reset means for discharging said capacitor in response to each of said trigger signals, the output of said flip-flop being coupled to said detector means.