Dynamic-biased control amplifiers for next generation communications

Abstract

The cellular telephones are technological marvels, and even more amazing features for these devices are on the horizon. These new features will include full screen real-time video, web browsing, and a variety of downloadable applications. However, these new features require much more power from the battery than existing cellular phones, and the resulting battery life will be unacceptable. The power amplifiers are classically the most power-hungry blocks in wireless communication systems. Bandwidth is luxurious, and more advanced technologies require transmission of maximum amount of information with minimum bandwidth usage. This requires advanced modulation schemes, leading to wide, dynamic signals that require linear amplification. Although linear amplification is achievable, it is always at the expense of the efficiency. Many of the modern wireless applications such as WCDMA use non-constant envelope modulation techniques with a high peak to average ratio. Since linearity is a crucial factor, RF power amplifiers implemented in such applications are obliged to operate at a backed-off region from saturation. Therefore, in order to overcome the obstacle of battery lifetime, a design of a high efficiency power amplifier that can maintain the linearity is the obvious solution. A new technique that improves the efficiency of a linear power amplifier has been investigated and demonstrated in this research. The Dynamic-biased control amplifiers technique consists of two amplifiers in parallel; in such a way that the combination enhances the power added efficiency of the main amplifier not sacrificing the linearity at the same time. Both high-power mode and low-power mode are presented. The classes of operation of two power amplifiers (A, AB, B, C etc), and the design techniques are presented. Design of a WCDMA power amplifier has been provided in Chapter 4. This technique shows a 560% increase in power added efficiency in the low power output region. This PA can be implemented in WCDMA cellular phone transmitters.