Current Feedback Compensation (CFC) Technique for Adaptively Adjusting the Phase Margin in Capacitor-Free LDO Regulators

Abstract

Current feedback compensation technique (CFC) can adaptively adjust the phase margin for achieving better transient response than that with variant phase margin at different load current conditions. Not only fast transient response is attained due to suitable phase margin but also the minimum load current limitation can be greatly reduced to about 50 mu A without sacrificing bandwidth at tight load current condition. Besides, CFC technique can have high PSRR bandwidth with compatible compensation capacitors compared to the Q-reduction technique [6]. The capacitor-free LDO regulator with CFC technique is fabricated by TSMC 0.35 mu m 2P4M CMOS process with small compensation capacitors 5pF and 1.5pF. Experimental results demonstrate that the minimum load can be reduced to 50 mu A and transient response time with adaptively phase margin control is smaller than 1 mu s.