| 摘要 |
PURPOSE:To prevent the inter-modulation of analog and digital modulating signals and to prevent the degradation of reception signal quality by mixing a local oscillator signal with the received signal for which an attenuation processing is performed, performing a frequency conversion and controlling attenuation amount by the output. CONSTITUTION:After radio waves where analog modulation signals and digital modulation signals to be transmitted from a prescribed transmission system coexist are received and the waves are converted by a low noise frequency conversion circuit, an attenuation processing is performed in a variable attenuation circuit 18, and local oscillator signals are mixed with the received signals for which the attenuation processing is performed, and the signals are converted into intermediate frequencies in a frequency mixer circuit 21. A distribution circuit 31 supplies these converted outputs to each of a band-pass filter 22 and an AGC voltage generation circuit 32. The band-pass filter 22 performs a band limit of the output of the frequency mixer circuit 21 and derives the output to a demodulation part via an amplifier circuit 23. The voltage generation circuit 32 generates control voltage so that the variable attenuation circuit 18 may have a prescribed attenuation amount based on the modulation signal level taken out from the front step of the band-pass filter 22 by the distribution circuit 31.
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