A complex band-pass filter for low-IF conversion DAB/T-DMB tuner with I/Q mismatch calibration
ABSTRACT This paper provides a complex band-pass filter (BPF) for low-IF conversion digital audio broadcasting (DAB) and terrestrial-digital multimedia broadcasting (T-DMB) tuner with I/Q gain and phase mismatch calibration. This calibration can be implemented in the first stage of complex BPF using feed-through resistor calibration scheme. The automatic tuning circuit with programmable clock is also presented. The measurement results show 1.536 MHz bandwidth with 2.048 MHz IF center frequency and 50 dB stop band attenuation at 0.7 MHz frequency offset. The in-band and out-band 3rd order intermodulation distortion (IMD3) are 55 and 60 dBc, respectively. After I/Q mismatch calibrating, 20 dB image rejection ratio (IRR) improvement is obtained from 38 dB to 58 dB in this work. The automatic tuning circuit guarantees less than +/- 4 % cut-off frequency variation covering the several clock requirements from demodulator ICs. The complex BPF is fabricated in 0.13 mum RF CMOS technology and consumes 9 mA with 1.2 V power supply.