A 1.1 GHz Fifth Order Active-LC Butterworth Type Equalizing Filter

This paper describes architectural and design considerations for low power, GHz range wideband low-pass active filters. A series LC resonator based biquad is proposed and its power efficiency is shown to be over 7 times better than an equivalent Gm-C biquad. Reduced number of active elements and readily available bandpass and low-pass signals make this topology particularly suitable for efficient realization of equalizing functions. Also demonstrated is a common-mode feedback scheme that allows for a stable, high accuracy common-mode control with loop bandwidth which can exceed twice the filter´s bandwidth. A fifth order active-LC Butterworth filter prototype is fabricated in a standard 0.18 CMOS technology. It provides a bandwidth of 1.1 GHz and features equalization gain programmable over a 0-23 dB range. It is experimentally verified to achieve 47 dB SNR and 48 dB IM3 with 250 mVpp swing while consuming 72 mW of power.