A CMOS 2 MHz self-calibrating bandpass filter for personal area networks

The design of a self-calibrating, tunable, channel select filter implemented in standard 0.25 μm CMOS technology for personal area network applications is presented. The active RC bandpass filter is used in a low-IF receiver with a 2 MHz IF. The filter architecture is a cascade of biquadratic (biquad) sections with low-Q resonators and transfer function s placed at interferer frequencies. A calibration technique adjusts for center frequency skewing by using the final biquad stage as an oscillator to track process variation. The filter has been successfully fabricated in the design of a fully-integrated, single-chip 2.4 GHz CMOS RFIC. The filter, with 16 dB of gain, features a 42 dBm equivalent input third-order intercept (IP3), when tested with out of band signals, and only 63 μV_rms input referred noise. 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.