| 摘要 |
PROBLEM TO BE SOLVED: To provide a direct conversion type semiconductor integrated circuit (a high-frequency LSI) for communication capable of improving reception sensibility by cancelling a DC offset generated by a self-mixing in a mixer circuit from the runaround of a local oscillation signal to an LNA input terminal. SOLUTION: In a direct conversion type reception circuit with a differential amplifier circuit (LNA 210) amplifying a reception signal, the mixer circuit (212) synthesizing the amplified reception signal and an oscillation signal having a specified frequency and conducting a frequency conversion and an amplifier circuit (220), to which a plurality of gain variable type amplifiers (PGA 1 to PGA 3) and a plurality of filter circuits (LPF 1 to LPF 4) eliminating the noises of the reception signal and unnecessary waves are connected at multistages and in which an amplification factor is constituted variably in response to the levels of the reception signal and which has a high gain, the reception circuit is constituted so that a low noise amplifier is brought to an unoperated state and the DC offset cancelling operation of the gain variable type amplifier on the pre-stage side of the high-gain amplifier circuit is carried out. In the reception circuit, the reception circuit is constituted so that the low noise amplifier is brought to an operated state and the DC offset cancel operation of the gain variable type amplifier at a final stage can be carried out. COPYRIGHT: (C)2005,JPO&NCIPI
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