Doherty Architectures in UHF
In the past, power amplifier blocks for UHF broadcast were straightforward to design. In most cases the requirement was a class AB broadband amplifier covering 470-860 MHz. A pallet approach (two transistors in balanced mode) was the most common implementation. Key parameters for this pallet are power (> 200 Wavg DVB-T), efficiency and linearity.
In the cellular industry, Doherty amplifiers were already introduced to enhance efficiency without too much cost increase and maintaining a small size. Because of its narrowband character, it required more time in the broadcast industry to switch over to Doherty amplifiers. Nowadays almost all new UHF transmitters make use of Doherty amplifiers. In recent years, new Doherty architectures have been developed which offer more efficiency and more bandwidth.
In this paper a brief discussion will be given to explain these new Doherty architectures and to help customers finding the best solution for their transmitter. Ampleon’s transistor family BLF8xx can support these Doherty architectures.
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