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Speech detection circuit
| Details |
Inventors: Komatsu, Noriyoshi; Aota, Masahiro; Komatsuda, Seiji; Ibuka, Toshihiro; Matsumoto, Yoshihiro;
Assignee: Fujitsu Limited (Kawasaki, JP)
Primary Examiner: MacDonald; Allen R.
Assistant Examiner: Sartori; M.
Attorney, Agent or Firm: Staas & Halsey
A speech detection circuit includes an amplifier for amplifying an input audio signal and having a variable gain, a rectifying circuit for rectifying an output signal of the amplifier, a comparator for comparing an output signal level of the rectifying circuit with a reference level, and a control circuit for outputting a control signal based on an output signal of the comparator. The control circuit outputs a control signal which indicates a power save mode after a predetermined time elapses from a time when the output signal level of the rectifying circuit becomes less than or equal to the reference level, and outputs a control signal which indicates a normal mode immediately when the output signal level of the rectifying circuit becomes greater than the reference level. The amplifier receives the control signal output from the control circuit and reduces its gain when the control signal indicates the power save mode. |
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DETAILED DESCRIPTION Accordingly, it is a general object of the present invention to provide a novel and useful speech detection circuit in which the problem described above is eliminated.
Another and more specific object of the present invention is to provide a speech detection circuit comprising amplifier means for amplifying an input audio signal and having a variable gain, rectifying circuit means, coupled to the amplifier means, for rectifying an output signal of the amplifier means, comparator means, coupled to the rectifying circuit means, for comparing an output signal level of the rectifying circuit means with a reference level, and control circuit means, coupled to the comparator means, for outputting a control signal based on an output signal of the comparator means, where the control circuit means outputs a control signal which indicates a power save mode after a predetermined time elapses from a time when the output signal level of the rectifying circuit means becomes less than or equal to the reference level, and outputs a control signal which indicates a normal mode immediately when the output signal level of the rectifying circuit means becomes greater than the reference level.
The amplifier means receives the control signal output from the control circuit means and reduces its gain when the control signal indicates the power save mode.
According to the speech detection circuit of the present invention, the gain of the amplifier means is smaller in the power save mode than in the normal mode, and the reference level of the comparator means at the time when the power save mode is cancelled is substantially increased to start and cancel the power save mode with a hysteresis characteristic.
For this reason, the power save mode will not be erroneously cancelled even when the input audio signal waveform varies from the reference level for the normal mode due to noise and the like.
Therefore, the characteristic of the circuit against noise is considerably improved in that the power save mode is cancelled immediately only when the input audio signal waveform reaches a reference level which is higher than that for the normal mode
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Audio Signal Processing 
