A 100-mA, 99.11% Current Efficiency, 2-mVpp Ripple Digitally Controlled LDO With Active Ripple Suppression

Digital low-dropout (DLDO) regulators are gaining attention due to their design scalability for distributed multiple voltage domain applications required in state-of-the-art systemon- chips. Due to the discrete nature of the output current and the discrete-time control loop, the steady-state response of the DLDO has inherent output voltage ripple. A hybrid DLDO (HD-LDO) with fast response and stable operation across a wide load range while reducing the output voltage ripple is proposed. In the HD-LDO, a DLDO and a low current analog ripple cancelation amplifier (RCA) work in parallel. The output dc of the RCA is sensed by a 2-bit analog-to-digital converter, and the digitized linear stage current is fed into the DLDO as an error signal. During load transients, a gear-shift controller enables fast transient response using dynamic load estimation. The DLDO suppresses the output dc of the RCA within its current resolution. With this arrangement, a majority of the dc load current is provided by the DLDO and the RCA supplies ripple cancelation current. The HD-LDO is designed and fabricated in a 180-nm CMOS technology, and occupies 0.697 mm(2) of the die area. The HD-LDO operates with an input voltage range of 1.43-2.0 V and an output voltage range of 1.0-1.57 V. At 100-mA load current, the HD-LDO achieves a current peak efficiency of 99.11% and a settling time of 15 clock periods with a 0.5-MHz clock for a current switching between 10 and 90 mA. The RCA suppresses fundamental, second, and third harmonics of the switching frequency by 13.7, 13.3, and 14.1 dB, respectively. Index Terms-Digital low-dropout (DLDO) regulator, hybrid DLDO (HD-LDO), LDO regulator, low ripple DLDO, ripple cancelation amplifier (RCA).