Apparatus and method for receiving a modulated radio frequency signal by converting the radio frequency signal to a very low intermediate frequency signal

摘要

A very low intermediate frequency (IF) transceiver is described for use in a wireless LAN, cellular telephone, cordless telephone, and other radio transceiver applications. The transceiver preferably directly down- converts the RF signal to lower frequency such as a very low IF signal, which can be handled by transceiver components advantageously integrated with the communication control system such as an MAC or serial communications controller. Preferably, the very low IF signal is above peak modulation deviation and below the channel interval for the communication system. The very low IF signal may be up converted so that the RF signal can be more reliably demodulated. Alternatively, the RF signal can be additionally converted to a second IF frequency before the very low IF frequency to reduce the effects of noise in the transceiver. Alternatively, an image rejection mixer circuit can be employed to provide some rejection selectivity for the adjacent channels on one side of the local oscillator. Alternatively, a phasing circuit can be added in the receiver front end to assist in the isolation of the local oscillator signal from the antenna.