| 摘要 |
PURPOSE:To obtain always the stable read-out data block amplitude voltage, by detecting the envelope waveform voltage of a read-out data signal and controlling the gain of a gain control circuit in response to the fluctuation of said envelope waveform voltage. CONSTITUTION:While a data block detecting circuit 7 is detecting a data block, the envelope waveform voltage is amplified by an amplifying circuit 12 and supplied as the gain control voltage signal of a gain control circuit 4. In other words, the gain of the circuit 4 is lowered at a part where the read-out data amplitude voltage is high and raised up at a part where said amplitude voltage is low respectively. Thus no envelope wavefrom voltage is supplied to the circuit 4 in the periods other than the data block. As a result, an envelope waveform is fed back to the circuit 4 to compensate the fluctuation of the envelope waveform voltage when a waveform which varies in terms of time is read out to the data block waveform voltage. In such a way, the stable read-out data block amplitude voltage can be always obtained. |
