Oversampled Pipeline A/D Converters With Mismatch Shaping

This thesis introduces a technique to improve the linearity of pipeline analog to digital converters (ADC). Through a combination of oversampling and mismatch shaping, the distortion introduced by component mismatch is modulated out of the input signal frequency band, where it can be removed by subsequent digital filters, significantly improving the linearity. Mismatch shaping can be realized in traditional 1-bit-per-stage pipeline ADCs, but suffers from some fundamental limitations, which limit its effectiveness at pushing the distortion out of band. These limitations can be alleviated by using a 1 bit/stage commutative feedback capacitor switching (CFCS) pipeline design, due to the properties of the CFCS ADC's transfer characteristic, which has reduced differential nonlinearity (DNL) and an even integral nonlinearity (INL). The CFCS converter offers the foundation for the implementation of many different algorithms for mismatch shaping, some with very simple circuit realizations. It is possible to generalize some of these ideas to multi-bit-per-stage pipelines, but with reduced effectiveness. A test-chip was fabricated in a 0.35pm CMOS process to demonstrate mismatch shaping in a 1-bit-per-stage CFCS pipeline ADC. The experimental results obtained from this chip indicate that the Spurious Free Dynamic Range (SFDR) improves by 8.5dB to 76dB when mismatch shaping is used at an oversampling ratio of 4 and a sampling rate of 61MHz. The Signal to Noise and Distortion Ratio (SNDR) improves by 3dB and the maximum Integral Nonlinearity (INL) decreases from 1.8LSB to 0.6LSB at the 12-bit level. Thesis Supervisor: Hae-Seung Lee Title: Professor of Electrical Engineering Acknowledgments This project was funded by DARPA under contract DAAL-01-95-K-3526, Analog Devices, Compaq, IBM, Intersil, Lucent Technologies, Maxim Integrated Products, Multilink, National Semiconductors Co., Philips Research Laboratories, Silicon Laboratories and Texas Instruments. I would like to thank my advisor, Prof. Hae-Seung Lee, for his invaluable guidance that has made my experience at MIT rich and fruitful. I am grateful to Paul Ferguson and Tom Barber for providing me access to Analog Devices' facilities and for always being very helpful. Kanti Bacrania was instrumental in having the test chip fabricated and packaged. His valuable suggestions on how to test the ADC and his help with FIB modifications have contributed to make this work possible. I am indebted to Andrew Karanicolas for his keen observations and his trouble shooting suggestions which helped me debug the first test chip. For their many technical discussions and help I would like to thank X. Haurie, Larry Singer, Dan Kelly, Stacy Ho, Jennifer Lloyd, Charles McDonald, Joseph Lutsky, Brian Brandt, Peter Holloway, Kush Gulati, Dan McMahill, Susan Dacy, Mark Spaeth, Mark Peng, Iliana Fujimori, Don Hitko, Andrew Wang, and Andrew Chen. I'm also grateful to Carolyn Collins for her patience and help throughout my time at MTL. I would like to thank my undergraduate advisor at KFUPM, Prof. Muhammad Tahir Abuelma'atti, for introducing me to circuit design. His dedication, remarkable personality and genuine care for his students have been a great source of inspiration. Being part of the MSA was one of the best aspects of being at MIT and I'm truly grateful to all the MSA members. Thanks also to the MBC boys and in particular to my apartment-mates Gassan, Jalal, Kashif and M. Saeed for many enjoyable times together. Special thanks to Rayyan and Reda for being such good friends. I would like to thank my nephews and nieces Sarah, Khadeejah, Aziz, Ahmed and Umar for being so wonderful. Thank you Maryam and Sumayyah for your continuous love, and thanks also to Anas. 'My Lord! bestow on them (my parents) thy Mercy even as they cherished me in childhood." (The Quran: The Night Journey) "All praise is due to God, the Lord of the Worlds. The Beneficent, the Merciful." (The Quran: The Opening)