User:Londonpenthouse/Envelope Tracking

Overview
Envelope Tracking is a technique for improving the efficiency of Radio Frequency (RF) Power Amplifiers (PA).

It works by modulating the power supply voltage to the final PA transistor, in line with the envelope (amplitude) of the signal being transmitted.

This can result in a significant improvement in efficiency, and consequent reduction in power consumption.

History
Envelope tracking as a technique for improving power efficiency of RF Power Amplifiers was first described by Bell Labs in 1937.

The practical challenges of implementing a highly efficient modulator delayed the implementation of commercial envelope tracking products, with the first commercially available implementations released in 2008.

Implementation Challenges
An Envelope Tracking modulator has to simultaneously satisfy four criteria:


 * Low Noise
 * High Bandwidth - typically up to 60 MHz for a 4G / LTE signal
 * High Power - a typical implementation may need to deliver up to 600W
 * High Efficiency - losses in the modulator should not offset the gains in the power amplifier

Efficiency increase
Envelope Tracking can significantly boost the efficiency of RF power amplifiers.

In July 2009, Nujira claimed that it had achieved a world-first efficiency of >60% for an 880MHz LTE Power Amplifier.