Doherty history, principles and key developments

The Doherty power amplifier has its origin from the pioneering work of William Doherty at Bell Laboratories in the 1930's where he investigated innovative methods of realizing efficient linear amplification at high power KW levels for transoceanic radiotelephony [1-2]. Over the ensuing decades and for most of the 20th century, the technique found popularity in AM broadcast transmitters, but more limited application elsewhere until the early 2000's and the advent and widespread deployment of modern cellular communications and digital broadcasting systems. Other key developments enabling Doherty architectures in these applications were advances in Si and III-V semiconductor device technologies to achieve higher performance RF amplification, and powerful digital signal processing (DSP) hardware and algorithms enabling distortion correction of the RF signal and amplifier linearization, thereby achieving efficient linear RF power amplification. This paper will examine underlying principles of Doherty PA operation, and highlight operational attributes and key developments which have resulted in it being the architecture of choice in today's cellular infrastructure transmitter.