Revisiting the Modeling of the Conversion Gain of CMOS Image Sensors with a New Stochastic Approach

Self Cite

A stochastic model for characterizing the conversion gain of Active Pixel Complementary metal–oxide–semiconductor (CMOS) image sensors (APS), assuming stationary conditions was recently presented in this journal. In this study, we extend the stochastic approach to non-stationary conditions. Non-stationary conditions occur in gated imaging applications. This new stochastic model, which is based on fundamental physical considerations, enlightens us with new insights into gated CMOS imaging, regardless of the sensor. The Signal-to-Noise Ratio (SNR) is simulated, allowing optimized performance. The conversion gain should be determined under stationary conditions.

Section: Numerical Modeling Of the Resultsmentioning

confidence: 99%

“…In this work, we address active gating where the sensor is a CMOS Image sensor, as described in our previous paper [11]. Gating is used for depth measurements and to achieve 3D imaging.…”

Section: Introductionmentioning

confidence: 99%

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Modeling Signal-to-Noise Ratio of CMOS Image Sensors with a Stochastic Approach under Non-Stationary Conditions

Cherniak,

Nemirovsky,

Nemirovsky

et al. 2023

Self Cite

“…For the MPV, a region of interest (ROI) { XE “region of interest:ROI” } of 100 × 100 pixels in the center of the exposed area was sampled and the values were averaged. Eventually, the system’s response curve was fitted using a linear equation of the following form [ 29 , 30 ]:

where a is the detector’s gain factor (G) and b is the pixel offset at zero DAK (no radiation).…”

Section: Methodsmentioning

confidence: 99%

A Novel Method for Developing Thin Resin Scintillator Screens and Application in an X-ray CMOS Imaging Sensor

Linardatos

Fountos

Valais

et al. 2023

Scintillating screens for X-ray imaging applications are prepared with various methods. Among them, the classic sedimentation method presents certain weak points. In this context, a novel fabrication process was developed that offers simplicity, economy of resources and time, while the screens exhibit adequate durability and image quality performance. The proposed technique involves a resin mixture that contains the phosphor in powder form (Gd2O2S:Tb in the present work) and graphite. The novel method was optimized and validated by coupling the screens to a complementary metal oxide semiconductor (CMOS) X-ray sensor. Indicatively, screens of two surface densities were examined; 34 mg/cm2 and 70 mg/cm2. Various established image quality metrics were calculated following the IEC 62220-1 international standard, including the detective quantum efficiency (DQE). Comparisons were carried out under the same conditions, with a sedimentation screen reported previously and a screen of wide commercial circulation (Carestream Min-R 2190). The novel screens exhibit has comparable or even better performance in image-quality metrics. The 34 mg/cm2 screen achieves a DQE 15–20% greater than its comparison counterpart, and its limiting resolution was 5.3 cycles/mm. The detector coupled to the 70 mg/cm2 screen achieved a DQE 10–24% greater than its own counterpart, and its limiting resolution was found to be 5.4 cycles/mm.

“…But for accurate measurements, like in some medical and scientific imaging fields, optical sensors require precise light intensity and frequency responses [ 6 ], where the linearity of the sensor becomes an important parameter. A lower level of nonlinearity can also enhance the accuracy of calculating parameters such as charge conversion gain or distance [ 7 , 8 ].…”

Section: Introductionmentioning

confidence: 99%

The Effect of Pixel Design and Operation Conditions on Linear Output Range of 4T CMOS Image Sensors

Zhang,

Xu,

Cheng

2024

We analyze several factors that affect the linear output range of CMOS image sensors, including charge transfer time, reset transistor supply voltage, the capacitance of integration capacitor, the n-well doping of the pinned photodiode (PPD) and the output buffer. The test chips are fabricated with 0.18 μm CMOS image sensor (CIS) process and comprise six channels. Channels B1 and B2 are 10 μm pixels and channels B3–B6 are 20 μm pixels, with corresponding pixel arrays of 1 × 2560 and 1 × 1280 respectively. The floating diffusion (FD) capacitance varies from 10 fF to 23.3 fF, and two different designs were employed for the n-well doping in PPD. The experimental results indicate that optimizing the FD capacitance and PPD design can enhance the linear output range by 37% and 32%, respectively. For larger pixel sizes, extending the transfer gate (TG) sampling time leads to an increase of over 60% in the linear output range. Furthermore, optimizing the design of the output buffer can alleviate restrictions on the linear output range. The lower reset voltage for noise reduction does not exhibit a significant impact on the linear output range. Furthermore, these methods can enhance the linear output range without significantly amplifying the readout noise. These findings indicate that the linear output range of pixels is not only influenced by pixel design but also by operational conditions. Finally, we conducted a detailed analysis of the impact of PPD n-well doping concentration and TG sampling time on the linear output range. This provides designers with a clear understanding of how nonlinearity is introduced into pixels, offering valuable insight in the design of highly linear pixels.