초저전력 RF 송신기 및 밀리미터웨이브용 전력증폭기에 관한 연구

Abstract

As the wireless communication technology advances, new standards are emerging. The new standards provide not only the fast data rate but also the new experience for the user, such as connected car, smart healthcare monitoring, object tracking and so on. One example is the wireless sensor networks (WSNs). This standard has severe energy constraint because the wearable sensors are spreading over a wide area and it is hard to recharge every time. Therefore, the size and power consumption should be minimized for the long operational life time. Another example is the 5G wireless communication. To handle the increased data throughput with the limited available frequency spectrum, millimeter-wave (mm-wave) power amplifier (PA) is considered. 5G system is expected to replace the 4G system with 1000 times more capacity and less latency. This dissertation describes an energy efficient ultra-low power (ULP) RF transmitter and highly linear and efficient mm-wave PA for the future wireless communication system. Three major works toward the emerging applications are explored in this dissertation. Firstly, a μW-level ULP RF on-off keying (OOK) transmitter is presented. Since the output power level of the short-range application is very low, the transmitter is optimized focusing on the efficiency enhancement at the low power operation. The low output power creates a problem of matching at a high impedance level, creating huge circuit loss of large inductances and susceptibility of small capacitances. To achieve the high efficiency without the loss of the matching inductance, a class-C PA with a shaped voltage drive is proposed. The small gain of the class-C operation is mitigated using the proposed driver with proper voltage shaping. Further, the architecture of the transmitter is simplified adopting OOK, not only avoiding the complexity of the system but also improving the efficiency of the PA by the constant envelope characteristic. Secondly, this dissertation deals with an ULP direct-conversion transmitter. This transmitter achieve faster data rate than OOK system by using the complex modulation signal, such as 16-quadrature amplitude modulation (16-QAM). Altough the power consumption itself is much higher than that of the OOK system due to the complexity of the system, the power consumption per bit can be lower. For low power implementation, a voltage-driven passive mixer based transmitter is developed. This architecture effectively reduces the power consumption benefiting from scale-down 28 nm CMOS process. In addtion, Doherty PA is used at the amplification stage, so the efficiency drop is minimized when the modulated signals with high peak-to-average-ratio (PAPR) are used. Finally, a highly linear mm-wave PA is presented. The recent trends toward 5G wireless communication are exploiting the mm-wave frequencies to handle the increased data volume. Here, fully-integrated 3-stage linear PA is proposed to enhance the limit of the efficiency and linearity trade-off. The second harmonic control circuit is employed and the sweet spot is properly employed to enhance the linearity of the PA. In addition, a low drop-out (LDO) regulator is proposed to eliminate the sideband asymmetry by the memory effect of the ultra-wideband signal. The LDO suppress the impedance at the envelope frequency up to 1 GHz, eliminating the external tantal capacitors. This integrated solution will be advantageous for the cost and size.