A5 . 6 μA Wide Bandwidth, High Power Supply Rejection Linear Low-Dropout Regulator With 68 dB of PSR Up To 2 MHz

Abstract

High power supply rejection (PSR) with a wide rejection frequency band is becoming a critical requirement in linear low-dropout regulators (LDOs) used in complex systems- on-chip (SOCs). Typical LDOs achieve higher PSR within their loop-bandwidth; however, their supply rejection performance degrades with reduced loop-gain outside their loop-bandwidth. Typical LDOs with external filtering capacitors may also have spectral peaking in their PSR response, causing excess system- level supply noise. This work presents an LDO design approach, which achieves a PSR of higher than 68 dB up to 2 MHz frequency and over a wide range of loads up to 250 mA. The wide PSR bandwidth is achieved using a current-mode feedforward ripple canceller (CFFRC) amplifier which provides up to 25 dB of PSR improvement. The feedforward path gain is inherently matched to the forward gain of the LDO, not requiring calibration. The LDO has a fast load transient response with a recovery time of 6.1 µs and has a quiescent current of 5.6 µA. For a full load transition, the LDO achieves settling with overshoot and undershoot voltages below 27.6 and 36.36 mV , respectively. The LDO is designed and fabricated in a 180 nm bipolar/CMOS/DMOS (BCD) technology. The CFFRC amplifier helps to achieve low quiescent power due to its inherent current mode nature, eliminating the need for supply ripple summing amplifiers and adaptive biasing.