Tunable band pass Gm-C filter with switched transconductance cells

In this paper, a technique for realizing a widely tunable band pass G_m- C filter is proposed by using output switched transconductance cells. This is suitable for low voltage applications. The proposed technique is applied to the design of a programmable second-order band pass G_m-C continuous-time filter with a center frequency, tunable from 10 to 120 MHz and is implemented in TSMC 0.18 mum CMOS process. To verify its effectiveness, the proposed filter and a filter using an alternative architecture reported in the literature, are implemented and their performances are compared. G_m/I_d design methodology is followed in designing the transconductor block. From the design and post layout simulation results, it is observed that the filter implemented using output switched transconductance approach results in lesser total harmonic distortion (THD) and supports larger signal swing compared to the alternative approach at the cost of marginal increase in power dissipation. The proposed approach guarantees the upper bound on THD to be -40 dB for a signal swing of 225 mV_pp.