Continued from Sony Develops 7.42-Mpixel Automotive Image Sensor (2)

Laminated design employed for cutting power consumption

To reduce power consumption, Sony employed a laminated design that forms a logic circuit part under the imaging part. Laminated types are often used for image sensors designed for smartphones, but the IMX324 is the first laminated-type automotive image sensor, the company said.

By separating the imaging part from the logic circuit part, it becomes possible to apply a more minute (advanced) manufacturing process to the logic circuit part. Though Sony did not disclose the details, it said, "We applied a process that is two or three generations more advanced that the processes used for existing automotive image sensor products."

With the advanced process, Sony reduced the power consumption of the logic circuit part and realized a power consumption of 500-600mW at a pixel count of 7.42 million and a frame rate of 40fps. If the sensor were not a laminated type, its power consumption would be 1W or higher, the company said.

Sensing cameras for ADASes and automatic braking systems are attached to the back side of a rear-view mirror. So, installation space is limited, and they are required to have a small size. In addition, their temperature tends to rise because they are heated by direct sunlight. Therefore, there are strong demands for reducing the heat generation and power consumption of their image sensors, Sony said.

Sensitivity changed for each frame

The IMX324 also features an enhanced sensitivity. The unit cell size of the imaging part is 2.25μm, which is small for an image sensor. However, the sensitivity (standard value: F5.6, accumulation: 1/30 second) of the sensor is 784mV in the standard mode and 2,666mV in the binning mode, in which four (2 x 2) pixels are bundled. Its dynamic range is 120dB.

This sensitivity is higher than that of the IMX224, which is Sony's existing high-sensitivity product (2,350mV). As a result, the new sensor can take clearer images in a dark (low-illuminance) environment, compared with the IMX224. The pixel count of images taken in the binning mode decreases by 75%.

A comparison of capability of taking images in the dark. The right image was taken with "IMX224," which is a previous product.

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