Design Considerations for Hybrid, Energy-Efficient, and Fast Industrial Power Amplifiers With Supply Modulation

In industrial applications, such as modern piezoelectric inkjet printers or automated device testers, arbitrary voltage waveforms need to be reproduced onto a different type of loads, providing four-quadrant operation with excellent linearity, preserving high signal-to-noise ratio with acceptable stability margin and high EMI immunity. These stringent requirements can be easily addressed if linear power amplifiers (LPAs) are employed. Nevertheless, their power density is limited by the large heat-sinks due to dissipative behavior of the Class A/AB/B output stage. In order to improve the performance of LPAs, hybrid PAs (HPA) are utilized, which involve highly efficient switched-mode power converters, called tracking power supplies (TPSs). In this article, the concept of HPAs based on only one TPS which modulates both supply rails is elaborated and exploited in two design examples, for different requirements regarding the output voltage dynamics. The first design is applicable in cases with a very fast output voltage dynamics (slew-rates up to 45 V/μs) and capacitive loads (piezoelectric nozzles), while the second design provides an optimized, very compact GaN-based solution in case when alleviated requirements regarding the output voltage dynamics (slew-rates up to 1 V/μs) have to be met for all types of passive loads (four-quadrant operation).