| 摘要 |
PURPOSE:To satisfy both the response speed and the stability of an output of a signal having a large peak factor by changing the time constant of a low pass filter in a level detection circuit in response to the output of the AGC circuit. CONSTITUTION:An input signal (a) is subject to absolute or square conversion by an amplitude detection circuit 1 and the result is sent to a low pass filter 2. In comparing a mean value output signal (c) with a prescribed value, the level of the input signal (a) is detected. Further, the input signal (a) is fed to an AGC circuit 10 comprising a multiplier 9, an amplitude detection circuit 6, a low pass filter 7 and a multiplicand detection circuit 8. An output (d) being the result of an output of the amplitude detection circuit 6 fed to the low pass filter 3 is compared with an output (e) of the low pass filter 7, its difference (f) is decided by a decision circuit 5 to change the time constant of the low pass filter 2. Thus, the response speed and the stability of an input signal having a large peak factor are improved.
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