Agilent 5991-0797EN English 2014-08-02 PDF 885 KB c20141023 [11] free download

File name 5991-0797EN English _ 2014-08-02 _ PDF 885 KB c20141023 [11].pdf

Keysight Technologies Solutions and Measurement Tools for Use in Average Power and Envelope Tracking Design Application Note Introduction With the advent of LTE, the transmission system in a cellular smartphone must process signals with both a very wide range of average power, to suit the user's location in the cell, and a high (8 dB) short term peak to average power ratio due to the nature of the LTE signal. Depending on the ampliier technology, the device may have to operate several dB below the level it would be capable of providing with a W-CDMA waveform. This comes at a time when battery capacity is already at a premium, heat dissipation within the handset is based on a budget and frequency coverage of multiple spectrum bands is required. The RF power ampliiers account for a signiicant portion of both the energy consumed and heat generated by the RF front end. Individual ampliiers may be required for each band. For- tunately, combining a multi-phase switched mode power supply with a high frequency linear ampliier enables an "on demand" approach to the supply voltage that can be used to deliver a useful reduction in both energy used and heat generated. With ampliier technologies having a soft AM/AM compression characteristic, supply modulation may also be used to signiicantly improve linearity. This reduces in-band and out-of-band intermodulation signals at higher powers. The use of boost mode in the SMPS to give transient increases in supply voltage enables further linearity improvements. This document provides an outline of the techniques involved and the solutions Keysight Technologies, Inc. provides for RF, baseband and system developers. Envelope Shaping PA supply PA input Magnitude ACP dB RF signal RF PA