| 摘要 |
PROBLEM TO BE SOLVED: To more accurately estimate a signal (reception) level, with a simple constitution. SOLUTION: An input signal IN is amplified by a plurality of amplification stages (for example, VAP1 to VAP3), and part of an output signal OUT in the final stage is detected, and the input signal level is detected on the basis of an AGC signal or a signal obtained by envelope detection of a signal in an arbitrary intermediate stage (for example, a point (a)) of a signal amplification circuit which performs AGC control of the gain of a plurality of amplification stages, so that the detection output is kept constant. In this signal level detection system, an amplification stage (for example, VAP1) which have a gain blind zone (namely, a part where the gain is not changed and is independent of the AFC input) for the common AGC input in a part, and amplification stages VAP2 and VAP3 which have no blind zones are cascoded connected.
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