A Programmable 210-μV Offset Rail-to-Rail Gm –C Filter

Low input-referred offset performance and linearity in analog filters are critical design parameters, yet transistor mismatch limitations are a severe hindrance. Programmability is also a feature of growing significance because high performance state-of-the-art systems must adapt on-the-fly to various operating conditions, as is the case in battery-operated electronics where systems traverse through idle, alert, and high performance modes in an effort to conserve energy and extend battery life. This paper presents a continuous and programmable first-order G_m-C filter with sub-millivolt offset performance. Low offset is achieved by auto-zeroing and continuity by ping-ponging between two transconductors, all under the construct of a compact and bandwidth-efficient circuit topology. The proposed G_m-C circuit was fabricated with AMI´s 0.5-mum CMOS process technology and achieved an input-referred offset of less than 210 muV, hand-over glitches of less than 40 mV, and 57 dB of linearity over the rail-to-rail input span for a lithium-ion battery supply range of 3 to 4.2 V. The bandwidth and gain of the filter were programmable from 1.1 to 6.5 kHz and 1.27 to 29.1 V/V, respectively, both with better than 3.2% resolution.