United States Patent m im Patent Number: 5,483,193
Kennedy et al.  Date of Patent: Jan. 9, 1996
 CIRCUIT FOR DEMODULATING FSK SIGNALS
 Inventors: John F. Kennedy, Dearborn; Scott O.
Campbell; Lawrence P. Kirk, both of
Canton, all of Mich.; David P. Laude,
Colorado Springs; Luke A. Perkins,
Security, both of Colo.
 Assignee: Ford Motor Company, Dearborn,
 Appl. No.: 409,397
 Filed: Mar. 24,1995
 Int. CI.6 H03D 3/00; H04L 27/00
 U.S. CI 329/300; 375/334; 340/825.31
 Field of Search 329/300-303,
329/341-343; 360/20, 27, 28, 30, 43, 48, 51; 375/334-337; 327/48, 49; 340/825.31,
 References Cited
U.S. PATENT DOCUMENTS
A circuit and method of demodulating an FSK signal uses digital circuitry to convert the received signal into count values. For each reception an adaptive reference count value is determined by averaging the duration of received pulses during the preamble of the transmission. The adaptive reference count corresponds to a demodulated logic "1" or logic level "0". The counts from the coded portion of the transmission are compared to the adaptive reference count. If the count is within predetermined windows from the reference count, the count value is converted to the corresponding digital signal.
20 Claims, 2 Drawing Sheets