Recent years have seen much progress in the integration of RF transceivers in low-cost CMOS technology, with many commercial transceivers on the market now being CMOS designs. However, it is still common in applications requiring high power output and high linearity to find discrete power amplifiers (PAs) implemented in other technologies. One of the obstacles to integrating the PA in CMOS is the linearity requirements of the nonconstant-envelope modulation schemes used in high data-rate systems. Linear class A or AB PAs have poor power efficiency compared to other topologies, but more power-efficient amplifiers such as class C, E, or Doherty configurations can only be used with constant-envelope modulation unless some form of linearization is utilized.

Cartesian Feedback is a well known linearization technique; however, its use in integrated transceivers has primarily been limited to either low output power or non-CMOS amplifiers. Existing analyses of Cartesian Feedback assume a linear amplifier as found in these designs, and do not offer useful intuition for application to highly nonlinear PAs as would be found in CMOS implementations.

This thesis investigates applying Cartesian Feedback to enable the use of a CMOS PA, allowing integration of the PA together with other radio components already available in CMOS. Contributions of this work include: development of analytical techniques applicable to highly nonlinear amplifiers leading to a stability criterion for the design of a Cartesian-Feedback loop; introduction of circuit techniques for CMOS implementations of PA, mixers and loop filter appropriate for the needs of Cartesian-Feedback; and application of these techniques to a monolithic transmitter for cellular telephone applications.

To demonstrate the validity of the developed analysis and circuits, an integrated CMOS transmitter, including an on-chip PA, was designed to produce an EDGE modulated signal. This prototype, implemented in a standard 0.18mm CMOS technology, meets GSM spectral mask and EVM requirements, producing an 18dBm output with 18% drain efficiency. The linearized prototype has distortion 21dB lower at 400kHz offset compared with open-loop operation, demonstrating the effectiveness of Cartesian Feedback for this application.




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