A 40–200 MHz programmable 4th-order Gm-C filter with auto-tuning system

Abstract

A CMOS 40-200 MHz 4th-order Gm-C Butterworth filter with an automatic tuning system for both frequency and quality factor is presented. Constant-capacitance scaled Gm-C integrators features a technique leading to a wide transconductance tuning range. A compact dummy-based scheme is also incorporated in the design to maintain the integrating capacitance constant over all the programming range. The filter is based on Gm-C biquads and the experimental results in a low-cost pure digital 0.35 mum CMOS process have shown a dynamic range of 58 dB for THD<-40 dB with a single 2 V supply. The cut-off frequency is digitally programmable in the range of 40-200 MHz. An automatic tuning system for both characteristic cut-off frequency and Q-factor is used to compensate for process and temperature parameter variations.