A Fast Transient Response Hybrid LDO With Highly Accurate DC Voltage Using Countable Bidirectional Binary Search and Soft Swap Switching

This brief proposes a fast transient response hybrid low dropout (LDO) regulator with highly accurate DC voltage for system-on-chip (SoC) applications. The proposed hybrid LDO, which consists of the analog and digital LDOs (ALDO and DLDO), and a hybrid controller, employs a hybrid algorithm in the hybrid controller to control the ALDO and DLDO so as to produce its accurately regulated output voltage. The proposed hybrid algorithm is realized with the countable bidirectional binary search (CBBS) and soft swap switching (SSS) through logic synthesis. The CBBS quickly determines the coarse-tuning current of the DLDO by controlling the number of turned-on switches in the DLDO, resulting in a fast transient response. In addition, the SSS precisely adjusts the fine-tuning current of the ALDO by controlling the moment when the ALDO is activated, resulting in a highly accurate DC voltage. The proposed hybrid LDO was fabricated using a 0.18-μm standard CMOS process technology. The measurement results show that the output of the hybrid LDO is regulated at 0.9 V when the input voltage ranges from 1.2 V to 1.8 V. In addition, the measured undershoot and overshoot voltages are 34 mV and 56 mV with the settling times of 68 ns and 344 ns, respectively, at a load current step of about 40 mA. Therefore, the proposed hybrid LDO is suitable for SoC applications requiring fast transient response and highly accurate DC voltage.