A Fast-Transient 500-mA Digitally Assisted Analog LDO With 30-μ V/mA Load Regulation and 0.0073-ps FoM in 65-nm CMOS

This article proposes a digitally assisted analog low-dropout (DA-ALDO) regulator, a hybrid solution which realizes tight regulation, wide load current range, area-efficient power transistor utilization, and fast transient speed in the meantime. The DA-ALDO employs an analog control scheme in steady state. Consequently, an accurate output voltage is available with a high-gain amplifier and no limit cycle oscillation occurs. A digital control scheme is invoked only upon transient events for speed enhancement, quiescent current reduction, and switching noise suppression. The digital controller adopts a hybrid algorithm of binary and multiple-unary schemes for an optimized tradeoff between voltage accuracy and settling time. The proposed DA-ALDO is fabricated in a 65-nm CMOS process with a maximum load current of 500 mA and a 250 pF on-chip output capacitor. Operating with an input of 1.2 V and outputs of 0.6-1.0 V and delivering from 500 mu A to 500 mA (or a 463x load current range with a current efficiency eta(c) > 90%), the DA-ALDO achieves 30-mu V/mA load regulation while consuming 120-mu A quiescent current. The measured undershoot/overshoot and the corresponding settling time with a 450-mA/100-ns load current step are 55 mV and 174 ns and 56 mV and 220 ns, respectively. The figure of merit (FoM) is as low as 0.0073 ps.

Automated summary

This article introduces a digitally assisted analog low-dropout (DA-ALDO) regulator, which achieves tight regulation, wide load current range, area-efficient power transistor utilization, and fast transient speed. The regulator utilizes an analog control scheme in steady state and invokes a digital control scheme only during transient events for speed enhancement, quiescent current reduction, and switching noise suppression. The DA-ALDO is fabricated in a 65-nm CMOS process, achieving 30-muV/mA load regulation with a 120-muA quiescent current, and demonstrating undershoot/overshoot and settling time with a 450-mA/100-ns load current step.