High Efficiency Amplifier

Abstract

In wireless communication system, power amplifier is one of the dispensable parts and consumes most of the power. As a result of this, high efficiency amplifier is desirable and many creative topologies are used to enhance the efficiency. In reality, efficiency enhancement can increase the lifetime of mobile phone’s battery and save energy for environment consideration. In this project, a linear amplifier, a distributed amplifier, a class A amplifier and a Class B amplifier are built as a foundation to understand the relative concept and be familiar with the technique of RF circuit. Based on these four amplifiers, a more complicated amplifier using a distributed amplifier and uneven biasing technique to cascade a class A and a class B amplifier to form a wideband high efficiency amplifier. Its gain is 10 dBm from 0.8 GHz to 2.2 GHz and efficiency is around 30% to 35% which is higher than conventional amplifier with only around 15% efficiency. Due to the consideration that power amplifier are usually required to work in backed off region from saturation power level for some signals such as WCDMA, Doherty amplifier is a optimal choice to solve this problem because of its relatively high efficiency in the backed off region. A Doherty power amplifier including a quadrature coupler, a Class B amplifier, a Class C amplifier and two quarter-wave transformer is built to achieve the efficiency enhancement goal. Its efficiency is around 60% for the peak value and more than 35% in the 6 dB back off point.