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

This paper presents an application of a fractionalorder 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 degrees. 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 degrees, the remaining phase margin is always at least 45 degrees. 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 mm(2). It operates in a harsh automotive environment with a temperature from -50 degrees C to 200 degrees 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).