The AB-C Doherty power amplifier. Part I: Theory

Abstract

In this article, the complete theoretical analysis of a Doherty amplifier employing a Class AB bias condition for the Main and a Class C one for the Auxiliary devices, respectively, is presented. Starting from the simplified model of an active device, the analysis of the AB-C Doherty behavior is carried out as a function of the input signal. In particular, the proposed approach is based on the analysis of the output drain current waveforms generated by the two active devices, while assuming a Tuned Load configuration (i.e., short circuit condition) for higher harmonic terminations. A closed form formulation is derived in order to directly design an AB-C Doherty amplifier, while fully understanding the basis of its physical behavior. Finally, which Doherty parameters can be chosen by the designer or have to be implicitly fixed are discussed and clarified.

A Method for Designing Broadband Doherty Power Amplifiers

“…These loading conditions, R M for the Main and R A for the Auxiliary, can be computed by the design requirements and active device characteristics [27]:…”

“…The output termination is placed on port 4, to interpose an odd number of λ/4 transmission line sections between it and the Main amplifier. This condition is mandatory to assure the decreasing of the output load seen by the Main amplifier in the OBO range [27]. Port 3 of the combiner is open circuit terminated to avoid power losses when the amplifiers are delivering different power levels.…”

Design of Unsymmetrical Doherty Power Amplifier for 460MHz LTE-Advanced Applications

“…Proceedings of the 2nd International Symposium on Computer, Communication, Control and Automation (ISCCCA-13) where C θ and P θ are the conduction angles of the carrier and the peaking amplifier respectively, and are related to the bias condition and input power level [8].…”

A 460 MHZ Doherty Amplifier for Imt-Advanced System

“…It can be deduced from (1) and (2), ideally, Z A moves gradually from 2Z 0 to Z 0 while Z C drops from a very high impedance value to Z 0 . Usually, the carrier amplifier is biased at class AB or B mode while the peaking amplifier is biased at class C mode [13]. In this case, the saturated power of the carrier and peaking amplifier is equivalent.…”