Due to the increasing demand of machine vision applications in a variety of scenarios, it is necessary to know the capability of the hardware before implementing it. The 1288 Standard by the European Machine Vision Association aims to provide a basis to compare the performance of cameras based on a characterization of the image sensor, using a monochrome light source. This paper aims to investigate the influence the light source has on the measurement results. Which parameters are dependent on it, and which are not? Are there any benefits to using a broadband light source? To answer this question, a series of measurement runs using six different illuminants were performed with the same camera. The illuminants included monochromatic blue, green and red light as well as three different white spectra (CIE E, CIE D65 and white LED). The results show that the influence of the light source on the metrics is limited to the measured quantum efficiency of the camera and related parameters. As a consequence, using a non-monochromatic light source for the measurements might be an option, as it can provide better insight into use-case specific performance and improve comparability.
A column-parallel 10-bit SAR ADC for high-speed image sensors has been implemented. A fast offset calibration technique using memory is proposed to compensate for the offset mismatch, accompanied by an ADC designed for a narrow space the size of a single column pitch. The memory accumulates the variation of the offset to track the offset within two cycles. After applying the offset calibration technique, the offset variation of the ADC measured in each column is improved from 4.27LSB to 0.39LSB. The fixed-pattern noise (FPN) is also improved from 4.14LSB to 0.34LSB. This calibration method covers an offset range of ±32LSB. The implemented ADC achieves a maximum speed of 500kS/s. The maximum frame rate of the sensor is 3000fps. The power consumption of the sensor, excluding the LVDS interface, is 71mW. This sensor is designed in a TowerJazz CIS 180nm process with one poly four metal. The supply voltage of the analog and digital domains is 3.3V and 1.8V, respectively.
A single chip Photoplethysmography(PPG) sensor was developed for continuous measurements of heart rate from a mobile device. In order to utilize it in various mobile applications, it was necessary to achieve low power and small size of PPG sensors. For low power and small chip size of the PPG sensor, a photodiode(PD) for sensing signals and an analog front end(AFE) for signal amplification and ADC should be implemented in a single chip. The single chip PPG sensor which is implemented on a standard CMOS process with low operating voltage could be more suitable for mobile devices. In order to operate at a low voltage, reduction of Si thickness is required, and for this, high quantum efficiency(QE) of 43% at 940nm were obtained at 3um thickness by back side trench(BST) pattern and ARL optimization. In addition, to improve the performance of the PPG sensor, the leakage current of <0.1nA and capacitance of <200pF were measured by 20um pixel array. As a result, the low-power, small size single-chip PPG sensor showed similar performance to conventional high-voltage and large PPG sensor.
Correlated Multiple Sampling (CMS), which is an extension of Correlated Double Sampling (CDS), is a very popular noise reduction technique used in the readout chain of image sensors. It has been analyzed in the literature, showing that, with an increasingly number M of samples, the total noise tends to a limit value dominated by the pixel 1/f noise. Nevertheless, this approach fails to explain why, in some cases, the total noise measurement may reach a minimum before, against all odds, finally growing with M. This paper shows that an explanation can be found if the pixel noise Power Spectral Density (PSD) varies in 1/fE with a frequency exponent E > 1 instead of E=1.