A stacked sensor is a type of image sensor used in digital cameras, including mirrorless cameras. It is called a “stacked” sensor because it is composed of multiple layers of photodetectors and other components, which are stacked on top of each other in a vertical arrangement. This design allows for a smaller, more compact sensor, as well as faster image processing and improved performance in certain areas.
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First, let’s start with the basics: What is an image sensor? An image sensor is the electronic component in a digital camera that converts light into electrical signals. These signals are then processed and converted into an image that can be stored and displayed.
There are two main types of image sensors: CCD (Charge-Coupled Device) and CMOS (Complementary Metal-Oxide-Semiconductor). Both have their own strengths and weaknesses, but CMOS sensors are generally more widely used today due to their lower power consumption and faster readout speeds.
Now, what is a stacked sensor? A stacked sensor is a type of CMOS image sensor that has additional layers of circuitry and memory stacked on top of the photodiode layer. The photodiode layer is the layer that captures light and converts it into electrical signals. By adding additional layers on top of the photodiode layer, a stacked sensor can offer several advantages over traditional CMOS sensors.
One major advantage of a stacked sensor is improved image quality. The additional layers on top of the photodiode layer can include circuitry for noise reduction, image processing, and other functions that can improve image quality. For example, Sony’s Exmor RS sensors use a stacked design with a DRAM layer for temporary storage of image data. This allows for faster readout speeds and improved low-light performance.
Another advantage is faster readout speeds. Traditional CMOS sensors read out each row of pixels sequentially, which can take time and result in motion artifacts (such as rolling shutter effects). Stacked sensors, on the other hand, can read out all pixels simultaneously, resulting in faster readout speeds and less motion artifacts.
These sensors can also offer higher resolution and faster frame rates. By adding more layers of circuitry, a stacked sensor can support higher pixel counts and faster frame rates than traditional CMOS sensors. For example, Sony’s IMX661 sensor is a 127-megapixel stacked sensor that can capture images at up to 21 frames per second.
Finally, stacked sensors can offer new features and capabilities that are not possible with traditional CMOS sensors. For example, Sony’s IMX990 sensor uses a stacked design with a dedicated AI processing unit. This allows for on-sensor AI processing of images, which can enable new features such as real-time object recognition and tracking.
In conclusion, stacked sensors are a type of image sensor that offer several advantages over traditional CMOS sensors. These advantages include improved image quality, faster readout speeds, higher resolution, and new features and capabilities.
Stacked sensors are becoming increasingly common in modern cameras, particularly in high-end models, and are likely to become even more prevalent in the future. As camera technology continues to evolve, stacked sensors will play an important role in driving innovation and improving the overall performance of digital cameras.
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