Efficient Design of Linear High-Frequency Filters

Direct-conversion receivers are becoming more and more popular in wireless communication systems because they promise superior performance in power consumption, size, and cost over existing heterodyne-based receivers. Theoretically, direct-conversion receivers offer the advantage of omitting the intermediate stage required in heterodyne architectures, thereby greatly reducing the hardware complexity of receiver design. In this research, a higher order filtering technique is proposed to attenuate out-of-band blockers in a direct-conversion receiver without deteriorating the desired signal present in the band of interest. The proposed filter structure is based on a current-mode biquadratic pipe filter cell, which originally allows the implementation of only all-pole filter functions such as Butterworth. With the aim to achieve a flat magnitude response in pass-band and steep rate of attenuation in transition-band, the base structure is modified to implement higher order Inverse-Chebyshev transfer function, which requires realization of arbitrary complex zeros in the stopband. A third order prototype has been realized in a 0.18¿m CMOS process using 1.8V supply voltage.