A modular approach to high-precision current amplifiers benefits lithography machines by reducing size and increasing efficiency. This research proposes two promising controller structures for a modular topology: a parallel controller structure and a cascaded controller structure. The study evaluates and compares their performance, introduces Delta-Sigma (DS) Analog-to-Digital Converters (ADCs) as a cost-effective alternative, and investigates their limitations in the proposed controller structures. A Feed Forward (FF) strategy is introduced to enhance the frequency response performance of both controllers.
Two methods to increase efficiency, particularly in amplifiers that are using interleaved Pulse-Width Modulation (PWM), are introduced: Phase-Shedding (PS) and Zero-Voltage Switching (ZVS). By estimating power losses it is shown that PS increases power efficiency for lower current setpoints, while ZVS increases efficiency for higher current setpoints. The study investigates how these methods impact controller stability and output current performance.
A hardware implementation validates the operation of the two controller structures. Stability issues with the cascaded controller structure become apparent and are resolved by a method that sacrifices bandwidth. Various measurements are conducted, and their results are compared to analytical expectations. The best frequency response is obtained using the parallel controller structure with a complex FF strategy, which gives a magnitude response of -0.3 dB and a phase shift of -3.6° at a 400 Hz setpoint.
When comparing the two controller structures, each has its own advantages and disadvantages. Choosing between the structures should be based on specific application requirements. If the application requires large bandwidth with high stability, the parallel controller should be selected. If the application requires good modularity, low quantization noise, and disturbance rejection performance, the cascaded controller should be selected.