Over the last decade, third-generation (3G) cellular networks have been undergoing tremendous development to meet an increasing demand for better quality and higher speed wireless services. Silicon germanium (SiGe) bipolar CMOS (BiCMOS) has been the dominant process technology for RF transceivers of cellular systems. However, in recent years, there is increasing interest to implement RF transceivers using advanced submicron CMOS technology driven by the demand for high-volume and low-cost solutions.
One big challenge for designing a CMOS WCDMA direct conversion transmitter is to meet the demand for both good linearity and good power efficiency. As opposed to constant envelop modulation adopted in GSM system, WCDMA employs HPSK modulation technique which presents better spectral efficiency but results in variable envelop modulation. Hence, linear amplification is required for WCDMA transmitter. Typically, power efficiency is traded for linearity performance. However, for cellular systems, low power solution is highly desirable for maximum usage of battery life. The goal of this research is to design a CMOS WCDMA transmitter with high power efficiency that is comparable to the SiGe BiCMOS counterpart while meeting the tough linearity specification.
In this thesis, a third-order intermodulation distortion (IMD) cancelation technique is developed to design a high power efficiency, highly linear operation and large out-put power transmitter for WCDMA systems. The third-order IMD cancelation approach is realized by using a two-stage driver amplifier, where amplifiers at the two stages amplifier generate opposite distortions and cancel each other. In this work, the nonlinearity of a CMOS common source amplifier is comprehensively investigated to set a solid ground for directing the design of two-stage driver amplifier with third-order IMD cancelation. One big challenge of two-stage driver amplifier with third-order IMD cancelation is how to maintain the third-order IMD cancelation over process and temperature variations. In this thesis, the required condition to realize third-order IMD cancelation is discussed over process and temperature variations, and the design criteria for achieving the third-order IMD cancelation over process and temperature variations are presented.
|Advisor:||Gard, Kevin G.|
|School:||North Carolina State University|
|School Location:||United States -- North Carolina|
|Source:||DAI-B 70/05, Dissertation Abstracts International|
|Keywords:||CMOS, Linearization, Power efficiency, Transmitter design, Two-stage IMD cancellation, WCDMA|
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