A 4th-order reconfigurable analog baseband filter for software-defined radio applications

This paper presents a 4th-order reconfigurable analog baseband filter for software-defined radios. The design exploits an active-RC low pass filter (LPF) structure with digital assistant, which is flexible for tunability of filter characteristics, such as cut-off frequency, selectivity, type, noise, gain and power. A novel reconfigurable operational amplifier is proposed to realize the optimization of noise and scalability of power dissipation. The chip was fabricated in an SMIC 0.13/μm CMOS process. The main filter and frequency calibration circuit occupy 1.8 ×0.8 mm<'2> and 0.48×0.25 mm<'2> areas, respectively. The measurement results indicate that the filter provides Butterworth and Chebyshev responses with a wide frequency tuning range from 280 kHz to 15 MHz and a gain range from 0 to 18 dB. An ⅡP3 of 29 dBm is achieved under a 1.2 V power supply. The input inferred noise density band (from 280 kHz to 3 MHz) and 8.74 mW for high band (from 3 to 15 MHz) mode.