Abstract
In this paper, a novel analog gamma correction scheme with a logarithmic image sensor dedicated to minimize the quantization noise of the high dynamic applications is presented. The proposed implementation exploits a non-linear voltage-controlled-oscillator (VCO) based analog-to-digital converter (ADC) to perform the gamma correction during the analog-to-digital conversion. As a result, the quantization noise does not increase while the same high dynamic range of logarithmic image sensor is preserved. Moreover, by combining the gamma correction with the analog-to-digital conversion, the silicon area and overall power consumption can be greatly reduced. The proposed gamma correction scheme is validated by the reported simulation results and the experimental results measured for our designed test structure, which is fabricated with 0.35 μm standard complementary-metal-oxide-semiconductor (CMOS) process.
Highlights
The past few years have witnessed the rapid development of complementary-metal-oxide-semiconductor (CMOS) image sensors and their wide range of applications in consumer electronics, such as digital cameras, camcorders, smart mobile phones, to name but a few [1]
We report an analog gamma correction scheme for logarithmic CMOS image sensor featuring high dynamic range
Compared with the previous implementations, the proposed analog gamma correction scheme exerts no amplification of the quantization errors
Summary
The past few years have witnessed the rapid development of complementary-metal-oxide-semiconductor (CMOS) image sensors and their wide range of applications in consumer electronics, such as digital cameras, camcorders, smart mobile phones, to name but a few [1]. As shown, when the input’s quantization step is smaller than that of the output, the system is disabled to generate the low luminance levels at the output [12] This issue can be addressed with higher resolution ADC, it can result in an exponential increase of storage amount dedicated to the direct lookup tables. Based on non-linear single slope ADC, two analog gamma correction schemes have been reported to avoid the amplification of the quantization error [13,14]. The proposed VCO-based ADC features a non-linear output approximate to typical gamma correction curve, which fully avoids the adopted ramp generator and the quantization error amplification in the previous implementations. The proposed gamma scheme is further applied to logarithmic image sensors to achieve high dynamic range and its effectiveness is validated by the reported simulation and experimental results.
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