CMOS High Q-enhanced Filters for Radio Receivers

Q-enhanced LC filters are presented as an alternative to off-chip filters in a High-IF type heterodyne receiver. The dynamic range limitations of this type of filter are analyzed and a closed form expression is given for the dynamic range given circuit parameters and operating Q. Test chips are implemented that include both on and off-chip inductors to obtain filters in the frequency range of 500 MHz and 2.4 GHz. The test chips use resistive degeneration to improve the linear range of the filter. Direct digital tuning of the filters is investigated and a test system is created to test the tuning capabilities. A dynamic range of over 40 dB is accomplished with a Q of 650, operating at 500 MHz using off-chip inductors. A dynamic range of over 30 dB is accomplished with a Q of 530, operating at 2.4 GHz using on-chip inductors.