Boots – shoes – and leggings
Patent
1989-11-06
1992-05-26
Black, Thomas G.
Boots, shoes, and leggings
379283, 34082574, H04M 150
Patent
active
051173697
ABSTRACT:
A DTMF receiver for a push-button telephone, a facsimile apparatus or the like is disclosed. The DTMF receiver comprises frequency shift delay detection units for lower and higher groups of frequencies. Each of said frequency shift delay detection units comprises: a circuit for generating a first signal and second signal having a frequency obtained by subtracting the reference carrier frequency from the frequency of the corresponding frequency group, the signal having a phase difference of .pi./2 with respect to said first signal; another circuit for generating a third signal and fourth signal which are different in phase from the first and second signals, respectively; a vector calculation circuit in which the first and second signals are supplied to one input port, and the third and fourth signals to the other input port; and a detection circuit for detecting a phase difference between the outputs of the vector calculation circuit.
REFERENCES:
patent: 3845249 (1974-10-01), Sellari, Jr.
patent: 4025730 (1977-05-01), Sawai
patent: 4143322 (1979-03-01), Shimamura
patent: 4347408 (1982-08-01), Ito et al.
patent: 4604755 (1986-08-01), Murray
patent: 4656648 (1987-04-01), Vallet
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