A Power-Efficient Adaptively-Biased Class-AB OTA with Improved Gain, Slew Rate, and Reduced Systematic Mismatch

This paper presents a high-performance powerefficient class-AB Operational Transconductance Amplifier (OTA) for biomedical applications. It features a DC gain of 80 dB, a unity-gain bandwidth of 214 kHz and a slew rate of $2 \mathrm{~V} / \mu \mathrm{S}$ driving 10 pF as load capacitor. High slew rate value is achieved by using an adaptive biasing, while drawing only $1.47 \mu \mathrm{~A}$ from a 1.8 V power supply. The proposed OTA is stable in unity-gain frequency with 63° phase margin, respected to the load capacitor. The design employs modified cascode current mirrors to achieve higher DC gain and reduce systematic mismatch. The proposed OTA is designed and post-layout simulated in a $0.18 \mu \mathrm{~m}$ CMOS technology. It achieved an input referred noise density of $57 \mathrm{nV} / \sqrt{ } \mathrm{Hz}$, a flicker noise corner frequency of $\mathbf{4 6 5 ~ H z}$, a common-mode rejection ratio of $\mathbf{8 1 ~ d B}$, a power supply rejection ratio of 94 dB and a total harmonic distortion of -59 dB. With adaptive biasing and a modified cascode current mirror, the proposed OTA reduced random offset voltage by $\mathbf{5 0 \%}$ and power consumption by $\mathbf{2 3 \%}$ in comparison with the conventional adaptive-biased structure.