A Fully-Integrated LDO with Two-Stage Cross-Coupled Error Amplifier for High-Speed Communications in 28-nm CMOS

This paper presents a fully-integrated flipped-voltage-follower-based low-dropout regulator (LDO), with proposed high-gain two-stage cross-coupled error amplifier (XCEA). Besides, the effectiveness of bypass capacitors and diversified load capacitors is discussed. Consuming
$\mathbf{170}-\boldsymbol{\mu} \mathbf{A}$
quiescent current and occupying area of 0.019 mm
²
, the LDO features 25-MHz unity-gain bandwidth (UGB) at 20-mA load to satisfy fast response requirement in high-speed transmitter. The simulated voltage undershoot is 38.85 mV for a load transient current stepping from
$\mathbf{1}\ \boldsymbol{\mu} \mathbf{A}$
to 25 mA in 50 ps with
$\boldsymbol{C}_{\mathbf{L}} =\mathbf{100}\ \mathbf{pF}$
. Owing to the proposed XCEA and the filter capacitor, the PSR is measured to be -41 dB at 100 kHz and -36 dB at 1 MHz.