Global Shutter Image Sensors

Stop Motion Quickly and Clearly

Introduction

Global shutter sensors have a fast and high-resolution capture of the entire field of view. Each pixel on a global shutter sensor completes its exposure simultaneously. This feature allows them to freeze motion in captured images. Each pixel will not only have the same integration time, but they will start their integration at the same time across the entire sensor. This exposure and detection scenario makes this type of sensor easier to synchronize with a flash or other external event.

On the other hand, rolling shutter models begin the consecutive exposure of single rows of pixels. Every pixel row will have the same exposure time; however, the first row starts its exposure prior to the last row of the captured image. This feature makes them susceptible to motion artifacts during the image capture of moving objects. Subsequently, they are often more cost-effective and advantageous for applications with slow moving scenes, or when actions are paused momentarily.

It is important to consider these criteria to determine the sensor that will provide the best quality and performance for your application, for example:

For more advanced applications, other factors that need to be taken into consideration are:

The evaluation of this criteria and attributes are important for designing an ideal image recording and image recognition system.

Pixel Architectures

Front Side Illuminated (FSI) Sensors

There is a wiring layer on the silicon substrate that forms the photodiode within FSI CMOS sensors. The benefit of this structure forms a light shield to keep leaked light away from the charged signal that is temporarily stored in the memory area. This sensor structure serves a dual purpose: 1) It transfers signal through the sensor; and, 2) provides a light shield for the memory. For this reason, conventional CMOS image sensors have adopted an FSI pixel structure. However, the wiring on top of the photodiode hinders incident light, which creates an issue during miniaturization of the pixels.

Back Side Illuminated (BSI) Sensors

Conventional CMOS image sensors mount the pixel section and analog logic circuit on top of the same chip. This configuration requires many constraints during the process of mounting the large-scale circuits. These constraints are measures to counter the circuit scale and chip size; to suppress the noise caused by the contiguous layout of the pixel and circuit section; and, to optimize the characteristics of both the pixels and the circuit transistors.

Image sensor designers have created the BSI sensor architecture to help overcome these drawbacks, above. In this configuration, the pixel’s circuit section is moved below the photosensitive area (pixel section), to allow more incoming light. This arrangement also allows the creation of smaller pixel configurations. Consequently, this feature leads to smaller, more compact sensors which enable both smaller sensors and larger resolutions to work with smaller optical formats. 

Other benefits of this structure are less cross talk between pixels, with better response times and more accurate color. Photons that enter the sensor quickly hit the pixel section to ensure that they are captured and correctly detected. Additionally, the pixel’s fill factor and the ratio of the photosensitive area to the total pixel area is much larger. These features reduce the requirements of the pixel’s micro-lens design (i.e., no increased refraction of the light to send it to the pixel); improves its CRA (Chief Ray Angle), while bringing the Bayer filter mask closer to the pixel. All these factors further improve the sensor’s image performance.

Pregius

Sony Pregius® Global Shutter Image Sensors

Pregius is a global shutter CMOS pixel technology based on Sony’s low-noise CCD structure which produces high-quality images in challenging lighting conditions or environments. 

Pregius technology represents the combination of the low-noise performance of CCD with the high-speed and high-precision performance (Precision) of the global shutter (GS) feature that is required by Factory Automation (FA) applications.

The digitization of the pixel data early in the transfer process is one of the major building blocks of the Pregius technology. This feature minimizes the amount of additional noise that is accumulated as the image data travels around within the sensor, even at high speed. Correlated double sampling (CDS), a technique borrowed from CCD design, is implemented on either side of the ADC (analog to digital conversion) to further improve the noise response of the sensor. This process cancels noise in the signal, ensuring the accuracy of the digitized data.

Sony has developed a proprietary pixel structure with global shutter functionality on a BSI structure that has superior sensitivity characteristics. Normally, when pixels are miniaturized, the sensitivity and saturation characteristics deteriorate. However, the new Sony technology enables a reduction in pixel size to 2.74 μm while maintaining the performance of BSI characteristics, thereby acquiring about 1.7 times higher resolution than conventional FSI CMOS sensors. Moreover, thanks to the high degree of the flexible wiring layout within BSI pixel structures, a high speed of about 2.4 times that of a conventional sensor can be determined. In addition, the sensor’s stacked structure makes it possible to mount various signal processing circuits. Consequently, it is possible to realize smart functions like signal processing only for the necessary part of the measurement and inspection images in a smaller size, compared to conventional sensors.

Sensor Functions and Features

Polarization

Polarization is an underused property of light; typically, its effect on surfaces and materials was managed through external filters in front of the camera. The inspection of objects with transparent packaging or highly reflective surface has been managed primarily with polarizing filters placed externally to the camera. Consequently, this method limits the incoming light to one polarization angle and does not allow the camera to capture light with different angles or under changing conditions. A variant of the IMX250, IMX253 and IMX264 sensors are available with additional polarization filters on each resident pixel. These filters transmit light in only one polarization direction. Four different directions are arranged in a 2×2 block of pixels, resulting in a 45⁰ polarization angle between each one; each captured image contains 4 different images. The degree and direction of polarization of the incoming light can be calculated with external processing. Subsequently, defects on complex shapes and/or reflecting surfaces can be recognized irrespective of the speckles that can appear with just one or two polarization angles.

Custom Global Sensor Options

Pyxalis® Global Shutter Sensors

Pyxalis specializes in designing and producing high performance custom global shutter image sensors with very high dynamic range, high speed frame rates, and deep color depth. They are well suited for demanding medical, science, surveillance, or industrial purposes.

Pyxalis offers these global shutter sensor platforms as-is or, as a starting point for a semi-custom design.

HDPYX 160-G and HDPYX 230-G Sensors

These Global Shutter sensors provide built-in pixel high-dynamic technology with a very high modulation transfer function (MTF), and feature artifact free HDR on-chip. Additionally, they are equipped with CDS for black level consistency, and feature two low-noise 11bit analog-to-digital converters (ADC). Video output is available in 8/10/12/14/16bits output format. These sensors also feature MIPI CSI-2 output (4 Lanes / 800Mbps) with a parallel output (12bits / 100 MHz), a serial communication interface, and integrated temperature sensors.

HDPYX 300 (Global/Rolling) Sensors

The HDPYX 300 feature these modes:

They are equipped with wide dynamic range capabilities and on-chip computing. These capabilities include in-pixel dual gain with automatic switch selection (Mode 1: 1 frame readout, true intra-scene HDR) and line-interlaced dual integration times (Mode 2: (odd/even) and configurable ratio, respectively). Other features include, Digital corrections, automatic column offset correction, and programmable digital gain and offset.

Want to learn more details about our custom GS Options? – Check out our complete portfolio of Pyxalis Sensors.

Global Shutter Sensors: Main Applications

Global shutter sensors have a fast and high-resolution capture of the entire field of view. Therefore, they are suitable for applications in Machine Vision and Industry 4.0, measurements and inspections, intelligent traffic systems (ITS), automotive, medicine, research, 3D, and stereo vision tasks.

FRAMOS OFFERS A RANGE OF GLOBAL SHUTTER SENSORS FOR YOUR VISION APPLICATIONS.