Gallium nitride class-F power amplifier for UMTSWCDMA applications

Abstract

The importance of wireless communications in today's telecommunications industry is indubitable. Wireless technologies are used in almost every aspect of our everyday life. Universal Mobile Telecommunications System (UMTS) technology has already implemented 3G communication standard for mobile communications. Power amplifiers are the most power consuming unit in wireless communication systems. The power amplifiers used in UMTS devices need to be highly efficient. Improved efficiency not only extends the battery life but also reduces the DC power consumption, transmitter size and weight. Although the power amplifiers used in existing second generation GSM (Global System for Mobile Communications) transmitters are highly efficient, they cannot be applied to UMTS/WCDMA since GSM uses the constant envelope feature of GMSK (Gaussian Minimum Shift Keying) modulation which introduces phase variations only. In UMTS, a WCDMA system with QPSK modulation is used where both phase and amplitude variations are introduced by the modulation. The power amplifiers designed for WCDMA need to satisfy the contradicting operation requirement between linearity and efficiency. In this thesis, a highly efficient class F power amplifier has been designed for WCDMA band with a center frequency of 2.14 GHz and bandwidth of 5 MHz using GaN transistor. The amplifier has been simulated using a high frequency circuit simulator namely, the Agilent Advanced Design System (ADS). The simulated results have shown a Power Added Efficiency (PAE) of 76.8% for an optimum input power of 30 dBm. The amplifier was then fabricated and measured. Measurement has shown a PAE of 75.9% for an optimum input power of 29.6 dBm which is in good accordance with the simulated results. Based on a literature review, and to the best of our knowledge, our circuit exhibited one of the highest measured PAE for a GaN class-F amplifier working at 2.14 GHz. The value of third and fifth order IM products of the designed class F PA is -13 dBc and -21 dBc respectively at peak power and -28.5 dBc and -43 dBc respectively at 6 dB back-off from peak power.