| The semiconductor industry continues to challenge analog and RFIC designers with a demand for higher performance and better compatibility with the digital world. It is desirable to use a single mainstream digital CMOS process for all IC products, especially for a system on a single chip. To achieve the highest integration, direct conversion for the analogue part is the most expedient candidate of all architectures because of its simplicity, and image-free and low power operation. However, the design of CMOS direct-conversion transceivers entails many difficulties: self-mixing induced DC offset, flicker noise, even-order distortion, I/Q mismatch, substrate noise, and so on. The aim in my research was to study these issues and to implement a prototype of direct conversion receivers with the proposed solutions.; On-chip crosstalk and substrate noise were studied firstly through simulations. It is shown that physical separation is pointless if no shielding schemes are adopted. Some effective shielding methods to reduce the crosstalk are proposed. Shielding achieved a 20∼40dB improvement on crosstalk. The flicker noise under switching conditions was studied experimentally for the first time. Methods to reduce flicker noise are discussed. The proposed simple noise model makes it possible to predict and optimize the circuit flicker noise performance. The severe self-mixing induced DC offset problem is circumvented completely by a proposed CMOS harmonic mixing technique. Two kinds of harmonic mixers in a CMOS process were designed and fabricated. The CMOS harmonic mixer achieved a 44dB DC-offset lower than do conventional mixers. Based on the harmonic mixing technique, the lateral bipolar mixer suppresses the flicker noise successfully and achieves less than 18dB noise figure at l0kHz frequency. They are totally DC offset free and suitable for direct-conversion receivers. Finally, a fully-integrated CMOS direct conversion pager receiver is demonstrated for the first time. |
