Increasing The Maximum Transmit Power Rating Of A Power Amplifier Using A Power Combining Technique

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•Application Note: Increasing The Maximum Transmit Power Rating Of A Power Amplifier Using A Power Combining Technique

By Skyworks Solutions, Inc.

Introduction

Today's broadband communications use high order modulation transmission links with a high crest factor. As a result, a linear Power Amplifier (PA) in the transmit chain operates at a significantly backed-off power from compression to meet the linearity performance of Error Vector Magnitude (EVM) and Adjacent Channel Power Ratio (ACPR).

The PA circuit is usually designed and optimized for a given rated transmit power to minimize current consumption. Portable electronics such as laptops and cell phones that integrate a broadband interface like WLAN need to be efficient. In these cases, the headroom, or margin to the maximum operating power of a PA that guarantees EVM and ACPR performance may be in the order of a single decibel. Therefore, usage of the device is limited to a fairly narrow power range.

This Application Note describes a method to extend the headroom of a PA by the use of a power combining technique. Power combiners and splitters are popular RF components that can be used to combine power from different sources, or to split RF receive signals for processing through different receive chains.

The first section of this Application Note presents the theory of power combining. It is demonstrated that combining the output of two identical PAs can increase the transmitter output power by a factor of 3 dB while maintaining the same level of linearity performance.

The second section provides an example that illustrates and verifies the theory of operation. It shows the results of combining two Skyworks SKY65152-11 PAs using a WLAN 802.11g test bench.

Click Here To Download:
•Application Note: Increasing The Maximum Transmit Power Rating Of A Power Amplifier Using A Power Combining Technique