Advances in Engineering Advances in Engineering features breaking research judged by Advances in Engineering advisory team to be of key importance in the Engineering field. Papers are selected from over 10,000 published each week from most peer reviewed journals.
Significance Statement
In the last decade CMOS image sensors (CIS) were constantly improving. These days they are comparable to CCD sensors in terms of image quality. Moreover CMOS processes enable the possibility of integrating intelligence at sensor level. Complex image processing algorithms can run on-chip in order to produce very high frame rate. The next step in the development of smart image sensors is to incorporate the ability to capture the depth of the scene. Single photon avalanche diodes (SPADs) arranged in bi-dimensional arrays are employed to associate the estimated time-of-flight with each corresponding point in the scene. When it comes to high frame rate the digitization of the time-of-flight needs to be performed at pixel level. If one have to characterize arrays of time-to-digital converters based on the statistical code density test, several TB of frames have to be captured and transferred to the computer to be analyzed. Capturing hundreds of millions of frames can take several weeks. The proposed technique based on a linear picosecond time interval generator to characterize large arrays of time-to-digital converters proved to be extremely efficient. Thus the memory footprint and acquisition time tremendously decreased down to few GB and a couple of tens of minutes respectively.
Journal Reference
Analog Integrated Circuits and Signal Processing, pp 1-9, 11 October 2015.
Ion Vornicu , Ricardo Carmona-Galán, Ángel Rodríguez-Vázquez.
Institute of Microelectronics of Seville (IMSE-CNM), CSIC-University of Seville, Seville, Spain.
Abstract:
Accurate generation of picosecond-resolution wide-range time intervals gives rise to a new time-efficient method for the characterization of large arrays of time-to-digital converters involved in time-resolved imaging. This paper presents the design and measurement of a time interval generator based on FPGA technology. Although it can be employed in different automatic test setups, it has been designed to characterize an array of time-to-digital converters. It can work as periodic pulse/frequency generator but also as a digital-to-time converter. The accuracy of the periodic pulse generator is around 20ps RMS jitter for a pulse-width ranging from 600ps to 33μs. The incremental time resolution is 8ps and the repetition rate is up to 2MHz. The digital-to-time converter error is less than 0.8LSB DNL and 2LSB INL, whilst the time resolution is 27ps. Full characterization of the module is reported including a comparison with state-of-the-art instruments in this field. The measurement results of the time-to-digital converter array driven by the designed digital-to-time converter module are presented as well. The effectiveness of the proposed method is evaluated by comparing it with the statistical code density test.
Go To Analog Integrated Circuits and Signal Processing
