IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences
Online ISSN : 1745-1337
Print ISSN : 0916-8508
Special Section on Analog Circuit Techniques and Related Topics
A High-Speed Column-Parallel Time-Digital Single-Slope ADC for CMOS Image Sensors
Nan LYUNing Mei YUHe Jiu ZHANG
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2016 Volume E99.A Issue 2 Pages 555-559

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Abstract

This letter presents a new time-digital single-slope ADC (TDSS) architecture for CMOS image sensors. In the proposed ADC, a conventional single-slope ADC is used in coarse phase and a time to digital convertor is employed in fine phase. Through second comparison of the two different slope voltages (discharge input voltage and ramp voltage), the proposed ADC achieves low bit precision compensation. Compared with multiple-ramp single-slope (MRSS) ADC, the proposed ADC not only has a simple digital judgment circuit, but also increases conversion speed without complicated structure of ramp generator. A 10-bit TDSS ADC consisting of 7-bit conventional single-slope ADC and 3-bit time to digital converter was realized in a 0.13µm CIS process. Simulations demonstrate that the conversion speed of a TDSS ADC is almost 3.5 times faster than that of a single-slope ADC.

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© 2016 The Institute of Electronics, Information and Communication Engineers
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