Advanced Control and Optimization Techniques for Integrated Switched Capacitor DC/DC Converters

Abstract

The rapid advancement in submicron technology increased the number of devices per die following the trajectory of Moore’s law. This increase in devices has led to an inevitable rise in voltage domains defined on-chip. This introduced a design challenge for an on-chip power management system, and switched-capacitor (SC) DC/DC converters have been one of the proposed solutions for this problem due to their inherent compatibility with CMOS technology and the moderate to high efficiencies they present. The control of these systems has been achieved via pulse frequency modulation techniques, specifically hysteretic control and voltage mode control algorithms. Both control techniques have been deeply rooted in the design of power management systems, but they also suffer from their shortcomings. This thesis proposes the use of time-mode processing techniques for the regulation of SC DC/DC converters. The difficulty in tuning the design parameters of a time-mode proportional-integral (T-PI) controller at the circuit level could lead to poor performance of the controller. Therefore, it is proposed that an automated design methodology could be used to tune those circuit parameters, which is done in a co-design environment between design tools (MATLAB - Cadence). The T-PI controller has achieved superior performance when compared with linear design methods (frequency-based), with an overall efficiency of 79.1%. Furthermore, it proposes a novel linear pseudo-differential architecture for T-PI, to relieve some of the challenges presented by differential Gm-based architecture. The proposed controller was fabricated in 180nm CMOS and occupied 2.57×1.77mm2 with an efficiency of 77.3%.

Finally, a new proposed controller is presented based on the P-only control algorithm called the adjustable setpoint proportional (ASP) control. The new proposed controller falls under the category of digital control systems, as it introduces a digital filter in the feedforward path to adjust the applied setpoint to the system. The proposed controller is claimed to have the pros of a proportional controller without its cons. The overall efficiency score was 70.81%, with settling times below the 1µs limit.