The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
May. 31, 1977
Filed:
Jun. 10, 1976
James Monroe Clark, Cedar Grove, NJ (US);
International Telephone and Telegraph Corporation, Nutley, NJ (US);
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.'