A 2-Vpp 80-200-MHz fourth-order continuous-time linear phase filter with automatic frequency tuning

A CMOS 80-200-MHz fourth-order continuous-time 0.05° equiripple linear phase filter with an automatic frequency tuning system is presented. An operational transconductance amplifier based on transistors operating in triode region is used and a circuit that combines common-mode feedback, common-mode feedforward, and adaptive bias is introduced. The chip was fabricated in a 0.35-μm process; filter experimental results have shown a total harmonic distortion less than -44 dB for a 2-V_pp differential input with a single 2.3-V power supply. The group delay ripple is less than 4% for frequencies up to 1.5 f_c. The frequency tuning error is below 5%.