The main function of LDO is to maintain constant output voltage which is equal to reference voltage VREF to sub-circuits in a system on Chip. There are analog LDOs that are suitable for noise sensitive load circuits. The disadvantage with Analog LDO is that is does provide sufficient loop gain at low supply voltages. The reason for insufficient. The different blocks of analog LDO are • Error Amplifier • Bandgap reference • PMOS Pass transistors and feedback loop. Digital LDOs are gaining significant attention because of low power and area constrained design. The D-LDO is composed of • Switch array • Comparator • Digital controller