A 220-nA Quiescent Current Capacitor-Less Low-Dropout Regulator with Improved Recovery Time

A 220 nA ultra-low quiescent current capacitorless low drop-out regulator (CL-LDO) with improved single transistor control (STC) and adaptive structural transformation is presented in this paper. The STC-LDO handles light-loads (<; 20 μA), whereas the adaptive transformation to a 2-stage structure handles moderate-load currents (20 μA-5 mA), and the subsequent transformation of the LDO to 3-stage structure handles high-load currents (5 mA-100 mA). The LDO provides a 0.9 V output voltage, and can regulate up to a maximum of 100 mA from a power supply of 1.1 V. Stability for the complete load current range (0-100 mA) was achieved at a maximum load capacitance of 100 pF. For a rising load current transient (0-100 mA), the LDO achieves a recovery time of 101 ns, and an undershoot of 292 mV is observed at the output. For a falling load current transient (100 mA-0), the LDO achieves a recovery time of 354 ns, and an overshoot of 56 mV is observed at the output. The CL-LDO is designed in a 40 nm CMOS process. The structural transformation proposed in this paper significantly improves the recovery time of the CL-LDO, enabling fast transient response even under ultra-low quiescent bias current of 220 nA.