A novel IF channel selection technique by analog-double quadrature sampling for complex low-IF receivers

This paper presents a novel IF channel selection technique for complex low-IF receivers. By utilizing the frequency-shifting characteristic of analog-double quadrature sampling (A-DQS), and setting the IF equal to half of the channel bandwidth, the desired channel and its image are neighbors and they can be selected to the baseband through simple control. Thus, the channel selection original performed by the front-end integer-N PLL frequency synthesizer can be partitioned to the A-DQS in the IF. The benefits of this partitioning channel selection method are 1) the step-size of the integer-N PLL frequency synthesizer can be doubled to two channels bandwidth in order to maintain low phase noise and fast settling time in very low-IF operation, 2) the locking position of the local oscillator in the entire frequency band is halved, since the frequency synthesizer only performs the frequency down-conversion of every two channels to the IF. Such technique is especially efficient in wireless receivers for 2.4 GHz 802.11b WLANs or Bluetooth that employ frequency-hopping to capture the signals.