| 摘要 |
A dual-mode cellular telephone system which is capable of suppressing a narrow-band disturbing signal appearing in a mobile station of a dual-mode cellular telephone system adapted for both an analog system and a digital CDMA system. A CDMA signal from a CDMA base station, and a narrow-band signal from an analog system are received through an antenna by a receiver, whereby they are amplified, subjected to frequency conversion, and input to a variable notch filter. A disturbing signal detection circuit supplies the variable notch filter with a control signal for varying its frequency. Namely, the disturbing signal detection circuit detects a case that an output level of the variable notch filter is at a minimum by changing the notch frequency via a series of sweeping control signals. A control signal at which the output level of the variable notch filter is at a minimum is then fed to the variable notch filter, thereby effectively suppressing any intermodulation distortions present in the mobile station.
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