Fully-integrated LDO voltage regulator for digital circuits

Low-dropout (LDO) voltage regulators are widely used to supply low-voltage digital circuits. For recent ultra-low-power microcontroller systems, a fully-integrated LDO without any external capacitance is preferred in order to achieve a fast and energy-efficient wake-up. Commonly, an LDO is specified, designed and verified for DC load currents. In contrast, a digital load creates large current spikes. As an LDO designed for low quiescent current is too slow to react on fast current spikes, a minimum on-chip capacitance is required to keep the supply voltage within a certain error window. Different fully-integrated LDO topologies are investigated regarding their suitability to supply low-voltage digital circuits. The any-load stable LDO topology is selected and implemented on a 0.13 μm test-chip. The LDO is able to provide a maximum load current of 2.5 mA while consuming a quiescent current of 17 μA.