Demodulators – Amplitude modulation demodulator – Having specific distortion – noise or other interference...
Patent
1976-06-10
1977-05-31
Grimm, Siegfried H.
Demodulators
Amplitude modulation demodulator
Having specific distortion, noise or other interference...
325320, 329107, 329122, 329126, H03D 300, H03K 906, H04L 2714
Patent
active
040272664
ABSTRACT:
The demodulator produces an inphase digital reference signal having the form cos A by means of an analog-to-digital converter and a quadrature digital reference signal having the form sin A by means of an N-stage shift register coupled to the converter. An inphase digital FSK signal having the form cos B is provided by a second analog-to-digital converter and a quadrature digital FSK signal having the form sin B is produced by a second N-stage shift register. A first read only memory responsive to the inphase and quadrature digital reference signals and the inphase and quadrature FSK signals produce an inphase code signal and a quadrature code signal for estimating the value of (B - A). A first M-stage shift register delays the inphase code signal and a second M-stage shift register delays the quadrature code signal. A second read only memory responsive to the inphase and quadrature code signals and the delayed inphase and quadrature code signals determine whether the value of (B - A) is increasing or decreasing. Logic gate means coupled to the two outputs of the second read only memory determines whether a first given code is detected more frequently than a second code and vice versa. A low pass filter coupled to the logic gate means averages the difference between the first and second given codes to produce a high voltage for a "mark" and a low voltage for a "space."
REFERENCES:
patent: 3600680 (1971-08-01), Maniere et al.
patent: 3979685 (1976-09-01), Motley et al.
Grimm Siegfried H.
Hill Alfred C.
International Telephone and Telegraph Corporation
O'Halloran John T.
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