Based On Cmos Technology Used In Wireless Lan 802.11a Protocol Quadrature Modulator Circuit Design

In the past few years, the wireless market has suddenly expanded to unimaginable dimensions. Devices such as pagers, cellular and cordless phoes, cable modems, and RF identification tags are rapidly penetrating all aspects of our lives, evolving from luxury items to indispensable tools. Meanwhile, with the rapid development of Internet and Network technologies, high-performance and large-capacity wireless communication systems are on demand greatly, among which wireless LAN is used widely because of its flexibility, convenience and efficiency. Therefore, the research on WLAN has been more and more attractive.The radio frequency (RF) integrated circuit is the design bottleneck of the WLAN systems. The viable IC technology for RF circuits continues to change. Performance, cost, and time to market are three critical factors influencing the choice of technologies in the competitive RF industry. Supported by the enormous momentum of the digital market, CMOS devices have achieved high transit frequencies. In the resent years, RF CMOS has suddenly become the topic of active research. In this paper, firstly the principle of modulator and mixer in wireless communication is introduced; subsequently different structures of mixer are presented. The merits and defects of these kinds of mixer are also discussed. Gilbert unit is widely used in modern RF receiver. This paper addresses the design of modified Gilbert unit. Common-mode feedback and linearized transimpedance technologies are used to improve the output voltage swing and linearity performance of conventional Gilbert unit in low voltage application.Noise factor is very important in the design of mixer. The definition, mechanism and calculation of noise factor are presented in this paper.A modulator for RF transmitter of 5-GHz WLAN has been realized using 0.18 μm CMOS technology in this paper. According to the test results, this modulator chip achieves the basic modulation function. At end, the thesis summarizes all the modulator circuit design, and has put forward the improvement scheme and emphasis and direction of the following work.