High efficient polar modulator for multiband and multimode RF transmitter

Abstract

Flexible transmitters handling multimode and multiband are inevitable for the evolution of the wireless communication system. Recent development in wireless communication devices has enabled the high-end voice-centric mobile phones to evolve into multimedia computers. Hence, compact radio architectures that are capable of operating in all radio systems are key elements when optimizing both development and manufacturing cost and performance of a multistandard wireless device. In this thesis, compact radio architectures, which have high linear, high efficiency, are studied. At first, a multiband and multimode RF amplitude modulator, which adopts the saturated amplifier for high efficiency, is studied. A multimode RF amplitude modulator and a digitally controlled variable attenuator are proposed and analyzed. With reference to a comprehensive analysis of nonlinear distortion, a current source modulated amplitude modulator was designed. Theoretical analysis indicates that the linear AM-to-AM and AM-to-PM transfer curve can be achieved by choosing the maximum amplitude region, $A_{max}$, which shows the minimum nonlinear coefficient, $a_1$, and reducing the LO leakage. Therefore, sufficient linearity can be achieved without the digital predistortion technique or a feedback loop. To improve the dynamic range and power consumption, a dual mode amplitude modulator is proposed. The passive mode operation of the VATT requires no dc power consumption. The proposed Π type attenuator yields good matching characteristics for the digitally controlled VATT. The wideband and digital controllability of the proposed VATT are more appropriate to the multi-mode RF transmitter than previously works. Multimode operations were tested with GSM, EDGE, and WCDMA signals. For the more compact radio architecture, there are two main approaches. One is the integration with a CMOS Power Amplifier (PA) and the other is migration with the RF function into digital domain. The digital intensive...