Method and circuit arrangement for identifying the presence or a

Details Method and circuit arrangement for identifying the presence or a Method and circuit arrangement for identifying the presence or a

1990-07-05

1991-02-05

Shepperd, John W.

Facsimile and static presentation processing

Facsimile

Specific signal processing circuitry

358196, 358144, 324 77B, 324 79R, 381 2, 381 7, 455132, 455137, 455214, H04N 560, H04N 704, G01R 2316, H04B 116

Patent

active

049910159

ABSTRACT:
A method and circuit arrangement identifies the presence or absence of known frequencies in an input signal composed of a plurality of frequencies, whereby a frequency generator controlled by a reference frequency generates four switch signals having frequencies dependent upon the frequency to be identified and having a phase difference of 90.degree. and respectively one switch signal is mixed with the input signal in a respective mixer. The respective mixer products of two mixers are additively combined and are filtered through a respective filter for filtering AC components out, and the DC voltage component contained in the respective mixer product given the presence of the known frequency is evaluated with respect to the amplitude.

REFERENCES:
patent: 3697878 (1972-10-01), Georgescu
patent: 3783413 (1974-01-01), Froment et al.
patent: 4139866 (1979-02-01), Wegner
patent: 4281411 (1981-07-01), Bonn et al.
patent: 4571622 (1986-02-01), Davidov et al.
patent: 4591915 (1986-05-01), Davidov et al.
patent: 4668910 (1987-05-01), Stepp
patent: 4710814 (1987-12-01), Gassmann et al.
patent: 4827515 (1989-05-01), Reich
Publication "Transmission of Two or More Sound Programmes or Information Channels in Television", Report 795-1, CCIR Documents, pp. 205-213, (1978-1982).
Article Kummel entitled "Zwei-Kanal-Fernsehton", publication Funckschau, No. 2, pp. 76-79, Jan. 1982.

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