How CMOS Sensors Breakthrough in Pixels and Size

Charge-coupled devices (CCDs) have been the dominant technology in digital imaging for many years, offering superior sensitivity, speed, and reliability. However, as manufacturing processes have improved, CMOS-based technologies have surpassed CCDs. Sony has noticed this trend. Ten years after it started in 2015, they decided to stop the process of CCD development.

Charge-coupled devices (CCDs) have been the dominant technology in digital imaging for many years, offering superior sensitivity, speed, and reliability. However, as manufacturing processes have improved, CMOS-based technologies have surpassed CCDs. Sony has noticed this trend. Ten years after it started in 2015, they decided to stop the process of CCD development.

CMOS image sensors have come a long way since Kodak’s early in-pixel charge transfer CMOS image sensors. Recently, Kodak’s CMOS image sensor won a Technology and Engineering Emmy Award.

How CMOS Sensors Breakthrough in Pixels and Size

Decades of breakthrough technology from Kodak paved the way for today’s CMOS-based image sensors.

As a testament to the accelerated innovation in this area, Sony and OmniVision have released new CMOS image sensors for different markets: industrial imaging and medical imaging.

How CMOS Sensors Breakthrough in Pixels and Size

A schematic diagram of a CMOS-based image sensor consisting of a photosensitive chip that is wired into an IC package.

Evaluating these new devices could provide a window into the direction of digital imaging and its subsequent impact on engineers working with CMOS image sensors.

Sony High-Resolution Image Sensors for Industrial Imaging

Sony recently released a large-format CMOS image sensor, the IMX661, which claims to have the “highest effective pixels in the industry”, reaching 128 million pixels. The feature of this product is to increase the number of pixels, making the optical size nearly 10 times larger than the ordinary 1.1-inch image sensor corresponding to the C-mount commonly used in industrial equipment, and adopts Sony’s original global shutter pixel technology “PregiusTM”, which can shoot without Motion distorted image. In addition, the use of Sony’s original device configuration and interface technology enables high-speed image reading data, which is nearly 4 times faster than the previous generation. What exactly does this number mean for engineers working in industrial imaging?

How CMOS Sensors Breakthrough in Pixels and Size

Increase die size without compromising resolution

There is an inverse relationship between pixel size sensitivity (a single active element of the sensor) and resolution relative to die size. The result is called an image format.

A popular standard for optical mounting is called C-mount and uses a 1.1″ format sensor, which doesn’t seem to fit in the IMX661’s 3.6-type package. Sony appears to be advertising its latest device as an alternative to c-mount optics, but with a much higher image resolution.

Global shutter is popular

The IMX661 sensor uses Sony’s proprietary technology “Pregius” to provide a global shutter. Unlike rolling shutters, global shutters allow the sensor to capture undistorted images of high-speed objects.

How CMOS Sensors Breakthrough in Pixels and Size

Global shutter is a feature that combats image distortion of objects moving relative to the pixel column.

While the readout into the processing unit is still continuous, the photosensitive elements are evenly exposed in a global shutter, ensuring that the scene is temporally sampled as a single frame.

Improve ADC conversion resolution

Readout into the processing unit is still continuous, and the photosensitive elements are evenly exposed in a global shutter, ensuring a scene is sampled as a single time frame.

The ability to improve ADC conversion resolution provides a great deal of design variability for applications with fixed and mobile cameras, such as automotive cameras.

OmniVision’s medical-grade sensors reduce invasive diagnostics

While Sony is ambitious in optics, OmniVision is also closing the gap between its medical-grade sensor lineup, while maintaining high standards in optical format, resolution, and power requirements.

Record-breaking sensor size

OmniVision has launched its newest CMOS image sensor, the OHOTA10, and OmniVision claims they have broken their own Guinness World Record for having “the world’s smallest commercial image sensor”. The new OHOTA10 reduces the size of the previous generation OV6948 from 575 μm2 to 550 μm2.

How CMOS Sensors Breakthrough in Pixels and Size

The OH01A uses the PureCel-S stacked chip architecture to meet the needs of next-generation disposable and reusable endoscopes and catheters, including small size, high resolution, and cost-effectiveness. The OH01A is the world’s first medical image sensor to provide 1280 x 800 resolution and 60 frames per second in a 2.5 x 1.5mm package size.

These properties of the OH01A make it an ideal imaging solution for many diagnostic endoscopic procedures, including airway management (esophagoscopy, laryngoscopy, thoracoscopy, pleuroscopy, bronchoscopy, mediastinoscopy) and urology (intrauterine renal mirror) applications, etc. “Because the catheters need to go into the body for diagnosis, doctors need smaller image sensors with higher resolution and the best image quality,” said Tehzeeb Gunja, chief marketing development manager at OmniVision. “At the same time, they need broad vision. Angle and close focus distance, and low power consumption to reduce heat and improve patient comfort. The OH01A image sensor meets all of these needs.”

The OH01A has a 1/11-inch optical size, 1.1 micron pixels and raw data output. It offers 1280 x 800 resolution and can also be resized to a 720p HD Display (16:9 aspect ratio) or an 800 x 800 square display. Both modes run at 60 frames per second, and images are crisp and jitter-free. The sensor’s PureCel-S stacked pixel architecture delivers the highest quality images with improved sensitivity, full well capacity, no halo and low color crosstalk.

The OH01A image sensor is also suitable for stereoscopic display applications, and two OH01A can run synchronously to provide 3D images for surgical procedures. Power consumption is also 25% lower than previous generation medical image sensors, resulting in cooler tip temperatures for endoscopes and greater patient comfort. In a small module, a high chief ray angle of 32 degrees provides a wider range of vision, allowing the use of shorter rigid endoscope tips and tighter bend radii.

Designed for minimally invasive probes

OmniVision anticipates that this new optical kit will open the door for designers to create smaller, minimally invasive probes for diagnostic applications.

Chenmeijing Liang, imaging technology and market analyst at Yole Développement, said: “These state-of-the-art CIS (CMOS image sensor) technologies are addressing today’s critical endoscopy needs, supporting physicians’ diagnostic process with higher image quality and better contrast. or surgical procedures while increasing patient comfort.”

How CMOS Sensors Breakthrough in Pixels and Size

“They also allow for less invasive imaging techniques for neurological, ENT or pediatric applications without changing the image resolution.”

Higher resolution, lower power consumption

In addition, the 42% pixel reduction triples the optical resolution, despite the reduced package size.

However, for the engineers designing these systems, the most gratifying improvements are the increase in power consumption, from 25mw to 20mw, and the reduction of the optical format from 1/36″ to 1/31″, which allows for a smaller package size.

Based on CMOS technology, they offer excellent noise immunity and dynamic range because they integrate amplifiers and convert analog signals to digital signals in the pixel columns.

It took decades for CMOS-based image sensors to replace CCDs as the primary optical sensor. However, with the improvement of optical wafer fabrication process and the reduction of pixel size, CMOS has become the mainstream technology today.

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