Frequency Compensation for Multistage Amplifiers Using Active-Feedback Current Buffers

A frequency compensation scheme based on an active-feedback current buffer (AFCB) is presented in this paper. With an active-feedback mechanism, the proposed AFCB offers quite low input impedance across wide frequency spectrum, which greatly reduces the power consumption of AFCB amplifiers employing the AFCB as frequency compensation. The bandwidth and slew rate of the AFCB amplifier are also improved due to the much smaller compensation capacitors. Moreover, the presence of a left-half-plane zero in the AFCB amplifier enhances the stability and settling behavior of the amplifier. A three-stage AFCB amplifier is implemented by a standard 0.18-mum CMOS process. When driving a 120-pF capacitive load, the AFCB amplifier achieves over 100-dB dc gain, 8.5-MHz gain-bandwidth product (GBW), 65deg phase margin, and 3.4-V/mus average slew rate with total 1.2-pF compensation capacitances, while only dissipating 88-muW power at a 1.5-V supply