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A simple method to reduce DC power consumption in CDMA RF power amplifiers through the LMV225 and an efficient switcher

Posted: 03 Mar 2008 ?? ?Print Version ?Bookmark and Share

Keywords:RF power amplifier? CDMA? 3G?

The need for higher wireless data rates is driving the migration of 2G to 3G mobile communication systems. The higher data rates in these systems impose additional performance constraints on the radio design of mobile phones.

In order to achieve the highest bandwidth efficiency of the allocated spectrum, these 3G mobile communication systems use spectrum efficient linear modulation schemes, such as Quadrature Phase Shift Keying, 8-Phase Shift Keying and Quadrature Amplitude Modulation.

In IS-95 and CDMA2000 systems, the RF power amplifier typically operates at 6- to 40dB back-off from the peak power or 1dB compression point. Consequently, the RF power amplifier operates with very low efficiency most of the time and is one of the most power consuming components in a handset. Studies show that the RF power amplifier consumes as much as 20 to 40 percent of the battery energy in regular phone operation.

This article presents a simple power tracking technique for efficiency enhancement in CDMA RF power amplifiers. This technique involves the use of a linear-in-dB RF power detector and a DC-DC converter switch. This enhancement scheme switches the DC supply voltage, VCC, of an RF power amplifier into two different levels through a DC/DC converter. National Semiconductor's RF power detector LMV225 determines the supply voltage of the RF power amplifier. An off-the-shelf CDMA2000 RF power amplifier can be used in this technique to improve the energy efficiency of the mobile phone.

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