Push-button signal receiving circuit and a method of...

Details Push-button signal receiving circuit and a method of... Push-button signal receiving circuit and a method of...

2005-09-06

2005-09-06

Tran, Sinh (Department: 2644)

Telephonic communications

Centralized switching system

Switching controlled in response to called station...

C379S283000

Reexamination Certificate

active

06940964

ABSTRACT:
A push-button signal receiving circuit and a push-button signal detection method are provided which can enhance frequency detection accuracy and yet can reduce erroneous determination as to the valid length of PB signal and thus erroneous operation. Valid signal determining portion determines the validity of a received PB signal in accordance with the results of determination as to the coincidence of continuance times of identification signals extracted by first and second frequency detecting portion for performing frequency detection over a small number of periods, and the coincidence of the frequencies detected by the first and second frequency detecting portion with those detected by third and fourth frequency detecting portion over a large number of periods.

REFERENCES:
patent: 4042789 (1977-08-01), Richards
patent: 5528663 (1996-06-01), Locke et al.

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