Analysis and comparative evaluation of stacked-Transistor half-bridge topologies implemented with 14 nm bulk CMOS technology

Abstract

Integrated Voltage Regulators (IVRs) have become a viable solution for microprocessor's power delivery. The active parts of the most recent IVRs are built in deep-submicron CMOS technologies and use stacked transistors to allow for the use of advanced low voltage devices with superior switching performance compared to the higher voltage long-channel devices. This paper evaluates three different topologies of CMOS half-bridge converters with respect to efficiency, implementation effort, suitability for on-chip integration, and multiphase applications: The conventional half-bridge converter, the half-bridge converter with conventional Active Neutral Point Clamping (ANPC), and a halfbridge converter with a modified circuit to achieve ANPC. In-depth analysis of the transient processes during switching for all three converters, based on Cadence simulations, reveal that both half-bridge converters with ANPC achieve proper balancing of the blocking voltages of the main transistors and are capable to attain similar efficiencies of 93% at an output power of 200 mW, input and output voltages of 1.6 V and 0.8 V, respectively, and a switching frequency of 150 MHz, which is 1% higher than the one attained with the conventional half-bridge converter. Of the two ANPC half-bridge converters, however, the proposed topology allows to completely turn off its entire power stage or parts of it, features less efficiency sensitivity to variations of dead-Time, and achieves the peak efficiency at relatively higher dead-Time values. These qualities render the proposed topology particularly suitable for multiphase systems and low load operation.