A self-calibrating bandpass filter and transceiver system tuning and test technique

The design of a self-calibrating, tunable, channel select filter and transceiver system tuning and test technique implemented in standard 0.25 μm CMOS technology for personal area network applications is presented. The active RC bandpass filter features a cascade of biquadratic sections and is used in a low-IF receiver with a 2 MHz IF. A calibration technique adjusts for center frequency skewing by using the final biquad stage as an oscillator to track process variation. The calibration approach is a hybrid of the direct frequency measurement and the master/slave approaches whereby the actual filter resonator is used as a voltage controlled oscillator without the need for additional master block circuitry thus minimizing complexity and die area. The bandpass filter is accessible within the receiver through an integrated test capability that allows for direct measurement of filter parameters. The filter has been successfully fabricated in the design of a fully-integrated, single-chip 2.4 GHz CMOS RFIC. The mean bandpass filter center frequency for a 20-chip lot is 2.0090 MHz with an 11 kHz standard deviation. The group delay ranges from 1.1 to 1.9 μs and the BPF consumes 7.4 mA from a 2.5 V supply under typical conditions.