Single-stage capacitor-less low-dropout voltage regulators with enhanced loop gain and PSR.

摘要

In this work, a LDO is proposed that has an extremely high gain error am- plifier implemented with a single-stage regulated telescopic amplifier. It is ex- perimentally proven that the regulated telescopic error amplifier contributed very high gain to the overall loop gain of the proposed LDO (denoted here Regulated Telescopic LDO), improving significantly its line and load regulation performance.;The performance of the proposed Regulated Telescopic LDO is compared to that of a Conventional LDO using Miller compensation and a Telescopic LDO using cascode compensation. The Conventional LDO is implemented using a differential pair error amplifier whereas the Telescopic LDO is implemented using a telescopic error amplifier. All the LDOs are designed using IBM 0.18 mum CMOS technology with 1.8 V input supply (Vs), 1.2 V reference voltage (VREF), 1.5 V output voltage ( VOUT), and for a load current varying from 1 muA to 100 mA. The PMOS, NMOS, and MPASS transistors have sizes of 10/0.36, 2/0.36 and 4800/0.18 (in mum) respectively. In order to keep the quiescent current consumption IQ of each LDO topology low, the error amplifier uses a bias current of 1 muA and the values of RFl and RF2 are selected so that 2 muA of it flows through them. A load capacitance CL=50 pF, a compensation capacitor CC=5 pF and a series nulling resistor RC=45 kO (Conventional LDO), 60 kO (Regulated Telescopic LDO) are used.;AC analysis is performed on all LDOs to capture the open-loop gain and phase responses. Phase margin PM≥ 50° is ensured over the wide range of load currents. The Regulated Telescopic LDO achieved extremely high loop-gain (AOL ≃ 121 to 140 dB) compared to that of Conventional LDO (AOL ≃ 38 to 54 dB) and Telescopic LDO (AOL ≃ 63 to 79 dB). As the loop gain of the Conventional and Telescopic LDOs is shown to be lower than that of the Regulated Telescopic LDO, they exhibited a low to modest voltage regulation. While the Regulated Telescopic LDO achieved extremely high voltage regulation. Line transient of each LDO is measured with rise and fall times of 10 ns for six load currents including 1 muA, 10 muA, 100 ,muA, 1 mA, 10 mA, and 100 mA. Load transient of each LDO is measured with rise and fall times of 10 ns for three load currents varying from 100 microA to 100 mA, 1 mA to 100 mA, and 10 mA to 100 mA. Simulation results are shown to verify that the Regulated Telescopic LDO has essentially improved line and load voltage regulation performance (by factors up to 63400 and 17000 respectively) w.r.t to the that of Conventional LDO. The Regulated Telescopic LDO also allows to use conventional cascode compensation which, in addition to a small capacitor added from supply to the feedback node (junction of RF 1 and RF2 feedback resistors), is shown to improve the PSR at DC up to 83 dB and at 20 kHz up to 25 dB. Experimental verification of the simulation results is obtained from chips fabricated through Mosis and the experimental results are in good agreement within the resolution of the measurement equipment.