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Low-dropout regulators (LDOs) are widely adopted in power management integrated circuits (PMICs) and serve as a bridge between the switching regulators and individual on-chip modules to provide a smooth, regulated output voltage. Compared to digital LDOs (DLDOs), analog LDOs (ALDOs) lead in the advantage of low output ripple and large power supply rejection (PSR). However, the preference of achieving high performance in terms of load transient, high PSR, good load and line regulation, while maintaining a low quiescent current and low dropout voltage for high efficiency, remains the key challenge in ALDO design. For operation with a low quiescent current, the bandwidth is reduced due to low transconductance, resulting in the limited gate driving capabilities in terms of charging and discharging the large gate capacitance of the pass or output transistor. In addition, the preference for system-on-chip design in the absence of large off-chip capacitors arises stability issues. In this paper, recent reported state-of-theart architectures for ALDOs are revisited and reviewed. The performance of these ALDOs is compared and their applications are investigated.INDEX TERMS Linear low-dropout regulators (LDOs), power management integrated circuits (PMICs), analog LDOs (ALDO), capacitor-less output, adaptive biasing, bulk modulation, power supply rejection (PSR), flipped voltage follower (FVF), charge pump.

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Purpose The purpose of this work in designing a wideband ring voltage-controlled oscillator (VCO) based on programmable current topology. It occupies a very tiny area yet achieving a good phase noise performance, which is suitable to be implemented in cost-effective and wideband frequency synthesizers. Design/methodology/approach The tuning range and gain are improved by dividing the VCO tuning curve into multiple curves controlled by programmable current sources without introducing additional parasitic capacitance. Findings Fabricated in 130-nm standard complementary metal oxide semiconductor technology and occupying an area of 0.079 mm2, the VCO is tunable from 2.05 to 4.19 GHz, with a tuning percentage of 68.5 per cent. The VCO measures a phase noise performance of −96.7 dBc/Hz at an offset of 1 MHz from a 4.19 GHz carrier while consuming an average current of 6.5 mA, achieving figure of merit (FoM) and FoMT of −158.9 and −175.6 dBc/Hz, respectively. Originality/value The proposed design uses programmable current topology without introducing parasitic capacitance, hence achieving wideband operation. It also occupies a tiny area and achieves a good phase noise performance.

Power-system state estimation is only possible if the network under study is topologically observable. A simplified technique is presented in the paper for solving the problem of power-system observability determination. The performance of the method is evaluated using several standard test systems.