Designing for UHF Broadcast Applications: The Need for Asymmetric Doherty Power Amplifiers

UHF broadcast transmitters that transmit digital TV signals (e.g., DVB – TUT2) are typically accomplished through the use of wideband push-pull class-AB power amplifiers (PAs). However, this approach limits the achieved average efficiency to roughly 25-30%. The challenge is that UHF broadcast systems have very high output power levels (typically Pavg of 0.5 – 3.0 kW) and this makes maximizing the broadcast efficiency extremely important to reducing overall operating cost. As a result, finding a high-efficiency alternative to the broadcast industry’s current RF PA blocks has become a chief concern. Asymmetric Doherty PAs offer a viable solution to this dilemma.

This webcast will discuss the advantages and disadvantages of Doherty amplification and symmetric versus asymmetric design. It will explain how an asymmetric Doherty approach can be used to design a high-efficiency, broadband PA that is suitable for UHF broadcast. For the purposes of this discussion, the design will utilize the Ampleon UHF transistor BLF888E and be created using Keysight Technologies’ Advanced Design System (ADS) software. Different implementations of an asymmetric Doherty approach for various frequency bands will also presented, along with achieved results.

Who should view:
Engineers designing high-efficiency PAs for UHF broadcast systems.

PRESENTER:
Bill Goumas, Principal Application Engineer
Bill Goumas is a Principal Application Engineer at Ampleon. His focus is on Aerospace & Defense and he also covers Broadcast and ISM Markets. He holds a BSEE degree in electrical engineering and has designed high power RF amplifiers for most of his 35 year career. He previously worked at Teledyne, Aethercomm, Nitronex, Crescend and Motorola. He has a wide range of experience with both LDMOS and GaN transistors and has worked up to 14 GHz and multi-kW power levels.