TOSHIBA has developed a circuit technique to remove distortion on wireless transmissions, which can be directly integrated into a CMOS radio frequency power amplifier.
Toshiba unveiled the technique on 20 February 20120 at the IEEE International Solid-State Circuits Conference. According to the company, this results in the first CMOS RF power amplifier integrating distortion-removal circuits.
All wireless communication standards used today utilise power amplifiers to amplify the output radio frequency signals. Moderating power use is critical to battery-powered devices like mobile phones and smart phones. RF power amplifiers in mobile phones are responsible for the consumption of a lot of power, thus the focus on improving the efficiency of that component.
Most of today’s power amplifiers are compound semiconductors which are large and difficult to fabricate.
While the golden grail is compact, easy to fabricate CMOS RF power amplifiers, these have proved difficult to achieve, because CMOS power amplifiers require a relatively large distortion correction circuit, which is too large to integrate.
Toshiba has successfully simplified and downsized the distortion correction circuit, allowing it to be integrated into a CMOS power amplifier, by identifying the threshold beyond which distortion degrades the RF signal.
Correction is applied only when the output power from the power amplifier exceeds 0.2W, the level required for communication with a relatively distant base station.
A CMOS power amplifier with the circuit improves the power efficiency 1.4 times (compared with a CMOS power amplifier test chip with the distortion correction function switched off, operating at the lowest power efficiency when antenna characteristics change 33% due to the external environment) , and secures high level RF signal stability by correcting distortion automatically.
Another plus is the increased versatility secured by removing the need for an external correction circuit that allows simple integration into the system design of a typical mobile phone.
Toshiba will first apply the CMOS power amplifier to WCDMA devices and also aims to apply it to next-generation communications standards.
