The Distortion Correction Circuit is Simplified in CMOS RF Power Amps

Published:2012/2/20 21:29:00 Author:Li xiao na From:SeekIC

As we know, the various wireless communication standards deployed nowadays use different ranges, but in all of them the output radio frequency signals are amplified by power amplifiers designed for these standards. The ideal solution must be compact, easy to fabricate CMOS RF power amplifiers, which is very difficult to achieve.

Battery-powered mobile phones and smartphones must sip power. The RF power amplifier boosts the signal and power of amplitude. The power consumption of the RF power amplifiers is large in mobile phones; therefore, high efficiency is very important for extension of the battery life. The compound semiconductors are usually used by the power amplifiers, but they are large and difficult to fabricate. A More compact alternative that is easier to fabricate can be provided by CMOS. However, CMOS power amplifiers need a distortion circuit that is relatively large, for it has to perform a huge number of calculations. The circuit is too large to integrate into the power amplifier or embed into a mobile phone.

The above problem can be solved by the circuitry developed by Toshiba. This circuit can be integrated into CMOS RF power amplifiers to remove distortion in wireless transmissions. Toshiba has been simplified and downsized the distortion correction circuit by identifying the threshold beyond which distortion degrades the RF signal. Only when the output power from the power amplifier exceeds 0.2W, the correction will be applied.

When compared with a CMOS power amplifier test chip with the distortion correction function switched off, the CMOS power amplifier with the circuit improves the power efficiency 1.4 times, operating at the lowest power efficiency when antenna characteristics change 33% due to the external environment. High level RF signal stability can be secured by the circuit. What is more, the external correction circuits are not needed; hence the circuit can be integrated into the system design of a typical mobile phone easily. This circuit will be used by the WCDMA devices firstly.

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