Sharp Kabushiki Kaisha Corporation

Michio Ikeuchi

Yasumoto Murata

Shuichi Yoshikawa

Masahiko Watanabe

Shuuichi Yoshikawa

Takahiko Nakano

Syuuichi Yoshikawa

A signal discrimination circuit judges whether an input signal contains a control signal or not, the control signal having a specific frequency and a specific level for a specific time duration. The signal discrimination circuit includes a component power detection device for detecting the power of a component which is in the input signal and having the specific frequency and a level judging device for determining whether the power of the component is equal to or greater than a power reference value. Finally, a control signal judging device is included for determining that the input signal includes the control signal, when the level judging device judges that the power of the component is equal to or greater than the power reference value, continuously for the duration of a reference time.

Signal discrimination circuit

A DTMF signal judging apparatus includes a first power calculator, and second power calculator and a judging apparatus. The first power calculator calculates the overall power of an input signal or the power of the input signal outside the DTMF frequency band. The second power calculator calculates the power in the DTMF frequency band; or more specifically, calculates the power in both the higher and lower frequency band portions of the DTMF frequency band. The judging apparatus then compares the output from the first and second calculators, and determines whether the input signal is a DTMF signal based on the comparison.

DTMF signal judging apparatus

A DTMF signal receiving apparatus includes a DTMF signal receiver; and a DTMF signal judging circuit. The DTMF signal receiver includes an input section for receiving an input signal from an external apparatus; a plurality of first band-pass filters connected to the input section; a plurality of second band-pass filters connected to the input section; and an output section connected to the plurality of the first band-pass filters and the plurality of the second band-pass filters, for outputting a code based on a plurality of outputs from the plurality of the first band-pass filters and the plurality of the second band-pass filters. The DTMF signal judging circuit includes a first judging device connected to the plurality of the first band-pass filters, for outputting a first judgment signal based on a plurality of first outputs from the plurality of the first band-pass filters; a second judging device connected to the plurality of the second band-pass filters, for outputting a second judgment signal based on a plurality of second outputs from the plurality of the second band-pass filters; and a third judging device for judging whether the input signal is a DTMF signal or not based on the first judgment signal and the second judgment signal and for permitting the output section to output the code when judging that the input signal is a DTMF signal.

DTMF signal receiving apparatus equipped with a DTMF signal judging

A signal discrimination circuit is provided with: a prediction circuit for releasing a prediction signal that is formed by making a linear prediction based on a previous input signal; a differential operation circuit for calculating the difference between the input signal and the prediction signal so as to release a predicted remainder; and a decision circuit for determining whether or not the degree of the variation of the predicted remainder from the zero level is maintained within a predetermined range. Therefore, even if a sound signal having a time-wise correlation and white noise having no time-wise correlation possess wide frequency components respectively, both of the signals are discriminated by the decision circuit based on the difference in the correlation. Thus, the signal discrimination circuit ensures an accurate discrimination between a control signal for a facsimile containing white noise and a sound signal.

A phase shift angle detector for detecting a phase shift angle of a multiphase modulated signal includes a first multiplier coupled with a first low pass filter for producing a cosine wave signal having a phase which is a sum of a phase shift .phi.e and the modulated signal g(t), and a second multiplier coupled with a second low pass filter for producing a sine wave signal having a phase which is a sum of a phase shift .phi.e and the modulated signal g(t). A circuit is provided for calculating an inverse tangent using the cosine wave signal and the sine wave signal to produce a signal representing the pahse shift .phi.e.

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Nara, Japan

Michio Ikeuchi