A Minimum-Voltage Driving Amplifier with Adaptive Three-Stage Open-Loop Gain and Folded Cascade Class-AB Output Current Control

摘要

A driving amplifier capable of operating at a minimum voltage is proposed, aiming to subdue the distortion effect caused by large amplitude driving at the hearing aid loudspeaker. Since the linearity of a cascode amplifier usually degrades with the reduced supply voltage, a three-stage cascade amplifier having a parallel cascade second stage, and a folded cascade Class-AB output current control in place are designed. With such an arrangement, the open loop gain should still be maintained at a sufficiently high level even in the presence of increased output amplitude. Also, the minimum supply voltage required can then be reduced to merely vertical bar V-GS vertical bar+2 vertical bar Vd(sat)vertical bar. Fabricated on a 0.18 mu m complementary metal oxide semiconductor (CMOS) process, the proposed amplifier achieves -72dB total harmonic distortion (THD)+noise(N) with a loudspeaker load of 100ohm while operating from a 1.2V supply and being subject to a 1kHz sinusoidal input.