A CMOS Follower-Type Voltage Regulator With a Distributed-Element Fractional-Order Control

Abstract

This paper presents an application of a fractional-order control in an on-chip follower-type 1.8 V/100 mA voltage regulator to achieve a good stability with any load capacitance. The controller approximates an integrator with the fractional order of 0.5, whose phase lag is not more than 45°. The fractional order is set by the fractional-order impedance of the resistive p-type MOS capacitor (R-PMOScap). With an n-type MOS source follower stage adding the phase lag of at most 90°, the remaining phase margin is always at least 45°. The R-PMOScap is a novel integrated distributed-element RC network, realized as a resistive polysilicon strip on a gate oxide, and is compatible with an analog CMOS process. The voltage regulator has been manufactured in a 350-nm CMOS process and occupies a small chip area of 0.038 mm2. It operates in a harsh automotive environment with a temperature from −50 °C to 200 °C and shows a tight DC regulation, while being stable over the full range of the load current (from 0 to 100 mA) and with any load capacitance (allowing to use none or any external capacitor).