Design of Reconfigurable Baseband Filter

Abstract

With the rapid development of worldwide wireless communication networks, mobile terminal devices compatible for multi-standard and various applications are needed. Software defined radio is a suitable answer to those demand. Baseband filter is one of the key building blocks in this device. And the baseband filter designed with tunable cutoff frequency gains a lot of popularity in recent years. A linear, reconfigurable fully differential CMOS transconductance-C filter is presented in this paper. The filter is implemented in 0.13um CMOS technology. It provides inverse-Chebyshev response and the cutoff frequency tuning range of the filter is from 4MHz to 40MHz. The transconductor adopts a folded-cascode structure and using gain boosting technique in the output stage to provide high output impedance. The input stage uses cross-coupled differential pair with bias offset to achieve high linearity. To be able to achieve the tuning capability of the filter, a floating voltage source with tunable value is employed. Cutoff frequency can be tuned by varying the floating voltage.