A 0.18 m CMOS CHANNEL SELECT FILTER USING Q-ENHANCEMENT TECHNIQUE

摘要

A channel select filter is designed in particular for the 3.6GHz range applications. The main function of the filter is to select a channel via a selecting voltage. It also provides a high gain for the selected bandwidth. The filter consists of an on-chip inductor in conjunction with an on-chip varactor. The varactor acts as a variable capacitor; the selecting voltage changes the junction capacitance of the varactor to shift the center frequency. The filter is implemented as an active BPF and provides about 5dB gain for the selected bandwidth while operates on 1.8Vdc. The gain and high passband selectivity are the results of the design of a high quality factor filter (few hundreds). A Q-enhancement circuit generates a negative impedance to compensate the low Q of the on-chip inductor and provides further selectivity. The Q of this filter is also a function of an external control voltage (i.e., tunable Q). This option offers bandwidth settings for various applications in the selected frequency range. The filter also provides a simple implementation of the receiver as it replaces the off-chip front-end filter and the LNA