Improving Multi-carrier PA Efficiency Using Envelope Tracking

Modern complex modulation schemes have the disadvantage of requiring linear power amplification characteristics, which compromises overall system efficiency because RF power amplifiers (RFPA) are much less efficient when operating in the linear region than they are at maximum power.

The power amplifier and its associated components consume up to 40% of the overall power in a cellular basestation and account for a similar proportion of operating costs.

Conventional designs for improving PA efficiency are inherently narrowband, requiring multiple amplifiers to be used in order to span all the required bands. This article describes a technique based on envelope tracking that has been proven to offer a dramatic improvement in efficiency, from typically 15% to over 50%, while offering multiband performance.

Continued evolution of the UMTS and WiMAX standards, and further evolved standards such as Long Term Evolution (LTE), are driving the need for multiple modulation schemes at multiple frequencies, and also demanding new spectrum to meet capacity demands. At the same time factors such as deregulation, the convergence of wireline and wireless carriers, and the appearance of new entrants to the market have created a surge in demand for equipment.

These complex schemes are a key factor in working towards the ultimate goal of global availability, but also place pressure on the OEMs to produce more frequency variants in higher volume, at lower prices, with