A MOSFET Switch-Based Reconfigurable Transitional Butterworth-Elliptic Filter

A reconfigurable transitional Butterworth-Elliptic filter based on MOSFET switch is presented in this paper. The proposed filter topology has the advantages of flat response in passband and fast roll-off in transition band. The reconfigurable characteristic is achieved by replacing the fixed capacitors with switch-capacitor networks. A proof-of-concept 5-order lowpass filter is implemented in 65-nm CMOS technology, with a core chip size of$\mathbf{0.193\ mm^{2}}$. The low-pass filter has 8 reconfigurable states covering the range of 2.5-4.7 GHz. In all states, the input return loss is better than 10 dB with over 25 dB stopband suppression.