”Backside illumination (BSI) is an image sensor design that uses its arrangement of imaging elements to increase the amount of light that’s captured, leading to improved low-light performance. While this type of design was previously used for things like astro cameras and security cameras, it has become a prominent technology in consumer still photography cameras.”
In 2015, Sony’s a7R II became the world’s first back-illuminated 35mm full frame camera. Last year, Nikon’s D850 became the first 45+ megapixel BSI sensor.
BSI CMOS sensors are all rolling shutters, this means the pixels in a photo aren’t all captured at exactly the same time but are instead captured by scanning across the scene very rapidly row-by-row. While this can produce identical results in most cases, it does cause distortions when the camera or subjects are moving rapidly during exposure.
A photo showing rolling shutter distortions in a rapidly spinning airplane propeller. Photo by Soren Ragsdale and licensed under CC BY 2.0.
But Sony’s newly developed sensor is a BSI sensor that has a global shutter function, allowing every single pixel in the frame to be captured at exactly the same time. Here’s an excerpt of the company’s technical explanation of its breakthrough design:
“The new Sony sensor comes with newly developed low-current, compact A/D converters positioned beneath each pixel. These A/D converters instantly convert the analog signal from all the simultaneously exposed pixels in parallel to a digital signal to temporarily store it in digital memory. This architecture eliminates focal plane distortion due to readout time shift, making it possible to provide a Global Shutter function”
To achieve the parallel A/D conversion for all pixels, Sony has developed a technology which makes it possible to include approximately three million Cu-Cu (copper-copper) connections in one sensor. The Cu-Cu connection provides electrical continuity between the pixel and logic substrate, while securing space for implementing as many as 1.46 million A/D converters, the same number as the effective megapixels, as well as the digital memory.
Here’s a sample photo Sony captured with the new sensor (notice how the spinning fan blades don’t exhibit any rolling shutter distortion):
No word yet on if or when we’ll be seeing this breakthrough CMOS sensor design show up in a consumer camera, but it’s clear that Sony is intent on staying ahead of the curve to continue its global dominance of image sensors and keep its digital cameras at the forefront of sensor quality.
Images by Petapixel.com
