A Large-Swing High-Driving Low-Power Class-AB Buffer Amplifier Employing Adaptive-Gain Error Amplifiers

Abstract

A large-swing, high-driving, low-power, class-AB buffer amplifier, which consists of a high-gain input stage and a unity-gain class-AB output stage, with low variation of quiescent current is proposed. The high-driving capability, low power consumption and low variation of the quiescent output current are achieved by using adaptive-gain error amplifiers whose gains are small in the vicinity of the stable state to reduce the power consumption and the variation of output current, while the high-driving capability is obtained by increasing the gains of the error amplifiers during the transient period. An experimental prototype buffer amplifier implemented in a 0.35-mum CMOS technology demonstrates that the circuit dissipates an average static power consumption of only 714 muW with the standard deviation of only 62 muW, which is only 8.7 % of the mean value at a power supply of 3.3 V, and exhibits the slew rates of 3.91 V/mus and 2.76 V/mus for the rising and falling edges, respectively, under a 100Omega/150 pF load. The second and third harmonic distortions (HD2 and HD3) are -70 dB and -66 dB at 20 KHz under the same load