A Low-Noise Output Capacitorless Low-Dropout Regulator With a Switched-RC Bandgap Reference

Low-noise linear regulators are critical for power supply regulation of noise-sensitive circuits, such as ADCs, phase-locked loops, and other mixed-signal/RF system-on-a-chip designs. A low-noise low-dropout (LN-LDO) regulator using switched-RC bandgap reference and a multiloop, unconditionally stable error amplifier for output capacitorless operation is presented in this paper. A sample-and-hold switched-RC filter is developed to reduce the noise of the bandgap reference and drain-side modulated current-mode chopping technique is proposed to reduce the flicker (1/f) noise of the error amplifier. A switched capacitor notch filter is utilized to filter out the residual chopping ripple of the error amplifier. Thermal noise of the current reference circuit which is significant at such low noise levels is also reduced by using a low-area penalty passive RC filter. These techniques reduce the total integrated output noise of the LDO in the 10 Hz to 100 kHz band from 95.3 mu V-RMS down to 14.8 mu V-RMS. The LDO delivers a maximum load current of 100 mA with a dropout voltage of 230 mV and a quiescent current consumption of 40 mu A. It achieves a power supply rejection of 50 dB at 10 kHz for a programmable output voltage range of 1-3.3 V. Fabricated in a 0.25 mu m CMOS process, the LDO core occupies an area of 0.18 mm(2).