| 摘要 |
PURPOSE:To preclude the possibility of generation of a read error or loss of correction in a succeeding demodulation circuit by detecting a level of an RF(HF) signal, comparing the level with a reference value and adjusting automatically the level of the RF(HF) signal in response to the difference. CONSTITUTION:The RF(HF) signal outputted from an amplifier 11 is fed to a synchronizing signal detecting circuit 15, and a synchronizing signal is detected from the signal demodulated there, and the detection signal is given to a level detection circuit 21. In this case, the level detection circuit 21 detects the level of the RF(HF) signal at that time and outputs a signal corresponding to the level to a control signal generating circuit 22. The control signal generating circuit 22 compares the signal from the level detection circuit 21 with a reference signal and gives a control signal corresponding to the difference to an adjusting means 23. The adjusting means 23 consists of, e.g., a variable resistor, which gives a resistance value corresponding to a control signal. As a result, the quantity of feedback of the amplifier 11 is changed and the level of the outputted RF(HF) signal is adjusted to be a reference value.
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