CMOS imager design for fast centroid readout

Abstract

Numerous applications of imaging systems involve the defemination ofthe centroid location of a localized region of high intensify (a "spot'7 that is easily distinguished from the background. The goal of the present work was to tailor the design of a custom CMOS imager to facilitate the centroid-location task. On-pixel circuity, readout methods, on-chip post-readout processing and other factors were considered in the design process. The 'design process' included system modeling, simulation and experimental validation as well as chip-level design.A triangulation rangefinder instrument was constructed to evaluate imager alternatives.The precision of the range determination is proportional to the precision of the location of the centroid of the image of an optical spot.Range measurements are presented to demonstrate that uncertainfy in centroid position, the dominant error source, can be significantly reduced by averaging. A novel CMOS imager design concept is described Using on-chip processing and a bixel-binav: rowkolumnparallel readout scheme, range values are expected to have an update rate as high as 1 MHz. Key aspects of the chip design are evaluated, especially as they pertain to update rate and the use of on-chip averaging to enhance precision.

Concept for image intensifier with CMOS imager output interface

“…These traces indicate that a simple threshold should eliminate virtually all NVG noise that does not originate at the photocathode. The pixel-binary CMOS imager 7,8 has a response time on the order of 10 µsec, which is 70x faster than the above decay time. Hence, such an imager can follow single photocathode events.…”

“…The architecture of the "pixel-binary" CMOS imager chip 7,8 is well-suited to the 'parallel' readout of centroid information in a time that is limited by the response time of the on-pixel comparators. A serial readout of analog pixel data is not needed in this architecture.…”

“…Pixel-binary imagers designed for rangefinding 8,16 can have an equivalent frame rate for the location of a centroid that is 10 5 Hz or faster. This high rate is achieved by on-pixel comparators and row-(and column-) parallel readouts followed by suitable on-chip processing.…”

“…Various temporal and spatial methods for outlier removal are identified in the table. Other factors of value in a rangefinder system include a time stamp, the ability to perform a calibration transformation, power control and averaging 8 . Although an on-chip solution is possible for these additional factors, some of them may also be readily implemented in programmable logic.…”

“…The dynamic range of the irradiance is improved by a higher frame rate. The "pixel-binary" custom CMOS imager 7,8 is expected to allow a centroid rate in excess of 10 5 Hz. "Region of interest" readout schemes can also facilitate a larger dynamic range.…”