| 摘要 |
PROBLEM TO BE SOLVED: To perform automatic gain control with high precision when a plurality of high frequency signals are amplified. SOLUTION: A plurality of high frequency signals are supplied to a variable attenuation section 2 and the level is adjusted depending on a control signal. An output signal from the variable attenuation section 2 amplified through amplification stages 4a and 4b is branched by one brancher 6. Frequency of a local oscillation signal to a mixer 10 receiving each high frequency signal is varied by controlling a voltage controlled oscillator 12 through a PLL circuit 14 such that each branched high frequency signal is converted into an intermediate frequency signal of the same frequency. Level of each intermediate frequency signal is detected by a level detector 22 and a CPU 26 detects the maximum level. A comparator 30 compares the intermediate frequency signal of maximum level with a reference level signal and the variable attenuation section 2 is controlled according to the comparison results. COPYRIGHT: (C)2008,JPO&INPIT
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