In-pixel autoexposure cmos aps

Abstract

A CMOS active pixel sensor (APS) with in-pixel autoexposure and a wide dynamic-range linear output is described. The chip features a unique architecture enabling a customized number of additional bits per pixel per readout, with minimal effect on the sensor spatial or temporal resolution. By utilizing multiple readouts via real-time feedback, each pixel in the field of view can automatically set an independent exposure time, according to its illumination. A customized, large increase in the dynamic range can be achieved and a scene containing both bright and dark regions can be captured. A prototype of 64 64 pixels has been fabricated using 1-poly 3-metal CMOS 0.5 m n-well process available through MOSIS. Power dissipation is 3.7 mW at = 5 V. The special functions have been verified experimentally, and an increase of 2 bits over the inherent dynamic range captured is shown.

CMOS Camera With In-Pixel Temporal Change Detection and ADC

“…The active load is comprised of a cascoded current source for high gain, and the output resistance is considered infinite in comparison to the resistance of the nMOS branch. The noise power contribution at the output from the pMOS current source is (12) For the access switch transistor (13) Lastly the input transistor's thermal noise contribution is (14) Referred to the comparator input, the comparator's noise contribution, 12 rms, is negligible. More significantly, the comparator introduces additional thermal noise components at reset and when the voltage at the is switched during computation.…”

“…Pixel-level ADCs offer several significant advantages [9], [10] since it eliminates the necessity of high-speed converters and outputting analog signals to external circuitry in addition to offering higher dynamic range [12], [14]. An image sensor operating autonomously must be able to adapt and function across a multitude of ambient lighting conditions.…”

“…Whereas biological systems enjoy upwards of 200 dB of dynamic range, typical CMOS image sensors can only achieve around 60 dB. Successful approaches to overcoming this limitation involve pixel level processing using variable rate integration time [12], taking multiple exposures [11] or outputting pixel saturation time [14], instead of a voltage. Biologically inspired imagers [13] have emulated octopus retinal systems by again using pixel level processing to output a time encoded intensity value, achieving wide dynamic range operation.…”

Smart camera design for realtime high dynamic range imaging

“…Several sensors development have been done with techniques such as well-capacity adjusting [1], time-to-saturation [2], or self-reset [3] (see [4] for a comparative analysis of these sensor architectures). To perform these functions, most of these sensors provide a processing unit at chip level or at column level [5]- [7], and even at pixel level [8]- [12]. The second method relies on conventional Low Dynamic Range (LDR) sensors to capture HDR data by recording multiple exposures of the same scene.…”

A flexible scheme for adaptive integration time control

“…Several approaches to build HDR imagers have been explored so far. The different concepts range from sensors with logarithmic response [1] or capacity adjusting schemes [2] to global or local multiple sampling techniques and others [3][4][5][6]. Many implementations explored so far suffer from a reduced signal-to-noise ratio or big pixel pitches resulting from a complex pixel circuitry.…”