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5 - Interactive loadline-based design of RF power amplifiers

Published online by Cambridge University Press:  05 July 2011

Patrick Roblin
Patrick Roblin
Affiliation:
Ohio State University
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Summary

The design of high-efficiency RF power amplifiers is of critical importance for wireless mobile devices and basestations. Design techniques that rely on circuit simulators are limited by the accuracy of the nonlinear large-signal models and by device package parasitics. Designing amplifiers using load-pull measurements is an alternative approach that bypasses the need for accurate device models. This chapter is concerned with the NVNA-assisted load-pull design of RF power amplifiers.

In this chapter, we will first compare the ideal and measured current and voltage waveforms, dynamic loadlines, and dynamic transfer characteristics for transistors operating in various fundamental amplifier classes (A–F). A multi-harmonic real-time active load-pull (RTALP) technique for the interactive design of the output-matching network will also be introduced and applied to the optimization of the amplifier power efficiency. The aim is to demonstrate how NVNAs can facilitate the design of power amplifiers by providing designers with greater insights into the actual mode of operation of the active devices.

Review of power amplifiers of various classes (A–F)

Class-A amplifiers provide a tradeoff between linearity and power efficiency. Specifically, they offer an excellent linearity at the price of poor efficiency because the device is on even when no RF signal is applied. The conceptual class-A circuit is shown in Figure 5.1 (a). An RFC is used to provide the supply voltage VDD to the transistor while blocking the RF from the DC supply circuit.

Type
Chapter
Information
Nonlinear RF Circuits and Nonlinear Vector Network Analyzers
Interactive Measurement and Design Techniques
 , pp. 124 - 159
Publisher: Cambridge University Press
Print publication year: 2011

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