| 摘要 |
If a local oscillation wave of a frequency approximately half the received signal frequency is input to a low noise amplifier 2, a dc offset voltage caused by the nonlinearity of the amplifier is produced, thus degrading reception sensitivity. This problem is resolved by disposing before the low noise amplifier 2 a filter means, such as a bandpass filter 12, band-elimination filter 13, or high pass filter 14, with characteristics for passing the received wave and suppressing a frequency band at approximately half the received wave frequency, thus preventing a radiation wave at substantially the same frequency as the local oscillation wave from being input to the low noise amplifier 2. A filter circuit 15 is also provided in the low noise amplifier 2 as a means for eliminating a radiation wave input to the low noise amplifier 2.
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