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 0.35m process; filter experimental results have shown a total harmonic distortion less than 44 dB for a 2-Vpp differential input with a single 2.3-V power supply. The group delay ripple is less than 4% for frequencies up to 1.5 . The frequency tuning error is below 5%.