High-Precision Power Converter with Ultra-High Effective Switching Frequency

Power amplifiers drive the linear and planar actuators in the high-precision motion systems used in lithography machines. These systems depend on fast, accurate motion control to achieve sub-nm precision when positioning silicon wafers. To achieve sub-nm positioning accuracy and a productivity of 200 wafers per hour, a new generation of ultra-high-precision power amplifiers is needed. These future amplifiers must provide precise output currents to prevent unwanted actuator force generation, deliver higher output power and bandwidth to maintain the throughput with larger and heavier handling systems for large-diameter wafers, and feature a compact size and low weight to minimize the mass and rigidity of the actuator drive cables. To quantify how power amplifier imperfections propagate into sub-nm motion errors, a multiphysics mechatronic model that links the control, mechanical, and electrical domains is presented. A fast and straightforward sensitivity analysis technique is used to evaluate how power amplifier errors—such as gain drift, non-linearity, noise, and current-loop bandwidth limitations—affect position accuracy. Moving-Average (MA), Moving-Standard-Deviation (MSD), and Moving-Root-Mean-Square (MRMS) position errors are used as accuracy metrics. The sensitivity analysis suggests that increasing the power amplifier bandwidth leads to reduced position errors. Therefore, the main focus of this research is on the design, simulation, and implementation of power amplifiers with high effective switching frequency and enhanced control bandwidth. After reviewing different families of switching power amplifiers, a dual-cell power amplifier solution is introduced. It consists of a main Low-Frequency High-Voltage (LF-HV) cell that provides the bulk of the output power, and a High-Frequency Low-Voltage (HF-LV) correction cell that enhances the small-signal bandwidth and enables accurate control of the output current or voltage. A decoupled control strategy is proposed and implemented on an FPGA, which increases bandwidth while preserving amplifier stability. The proposed power amplifier is designed by selecting the HF–LV cell’s switching frequency to maximize bandwidth for next-generation precision systems, while its supply voltage and inductance are set based on reference signal dynamics and ZVS requirements. For the LF–HV cell, the optimization aims to determine the switching frequency and inductance that minimize the loss–volume product. Finally, the filter capacitances are defined by the cut-off frequencies. A key challenge in increasing the switching frequency is the reduction of the digital PWM resolution. This work introduces two FPGA-based high-resolution digital PWM schemes to address this: first, a resource-efficient single-path design, and second, a cascaded design that enhances resolution and/or allows lower clock speeds. Both, implemented on an Artix-7 FPGA, provide temperature-immune pulse widths and support high-accuracy duty-cycle and dead-time updates twice per switching cycle. The cascaded design achieves 39 ps time resolution at 400 MHz. Finally, the proposed power amplifier is experimentally validated through step-response measurements, mixed and pure sinusoidal reference tracking, and fourth-order trajectory tracking using both resistive and inductive loads. The current step-response test shows a rise time of about 1.5 µs and a settling time of approximately 90 µs. Tracking mixed sinusoidal references confirms the amplifier’s ability to accurately follow high-frequency components. A Total Harmonic Distortion (THD) of around $-100~\mathrm{dB}$ is achieved across the first 150 harmonics when tracking a sinusoidal current reference. The fourth-order trajectory tracking demonstrates that the HF-LV cell effectively compensates for high-frequency harmonics, while the LF-HV cell ensures stable low-frequency control, keeping the expected MRMS error well below $20~\mathrm{pm}$.