Broadband Doherty Power Amplifier using Symmetrical GaN Transistors
The wireless industry has seen a tremendous growth in its users over the last decade. This has led the industry to adapt a number of new standards allowing for better use of the scarce and often very fragmented frequency spectrum.  The new standards have brought with them the use of OFDM signaling to allow for higher data rates and better robustness against frequency selective channel interference. The OFDM protocols combined with multi-standard radios however have provided many challenges to the radio frequency, RF, industry with the largest challenge presented to the power amplifier design. The OFDM signals are well known for their high peak to average power ratio which forces the RF equipment to work at significant back-off compared to peak power. This unfortunately leads to rather low system efficiencies.
To address the problem the Doherty power amplifier has been brought back into the design community as it directly solves the issues related to average power efficiency. To date however many of the Doherty designs have focused on the narrowband application of the power amplifier often targeting a single standard with bandwidths directly tied to the operational band which at best is usually only couple hundred MHz wide. With the recent changes in the standards and the ever growing desire to provide several standards on one radio the Doherty has to be redesigned to allow for broadband communications.