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Introduction to SONY’s Dual Pixel AF 2016-08-09

Smart phones have now become an indispensable part of people’s everyday lives. The trend for smart phones is therefore an evolution towards ultra-slim and high resolutions. The specifications of the phone's camera function have become increasingly important to customers as well, leading to camera specifications and technologies that were once the exclusive province of digital cameras being gradually transplanted to smart phone cameras as well. The speed and accuracy of the focusing function in smart phone cameras is constantly being tweaked to try and satisfy customer requirements. Contrast Auto Focus (AF) contrasts images to determine the correct focal distance and is in common use. The Dual Pixel AF photo-sensor developed by SONY promises to increase the focusing speed even more.

The basis of Dual Pixel AF is that every pixel on a CMOS photo-sensor contains two photo diodes - this is known as Dual Photo Diodes (PD). In this type of sensor, each pixel has two PDs that we call PDL and PDR. The Dual PD sensor can focus quickly and accurately like the human eye which as we all know, focuses by comparing the images seen in both eyes. In each pixel, the PDL is like the human left eye while the PDR is like the human right eye. When the sensor is in operation, PDL and PDR can both capture their own light rays. This CMOS is not just responsible for receiving the image but also for auto-focusing using Phase Difference. Figure 1 shows the Sony photo sensor with a focusing pixel in place. The CMOS photo sensor's phase pixel picks up the differences in light wave information sent from the left and right in order to determine the phase difference created by distance.

                                                                               (figure 1)

The advantage of the Dual Pixel photo sensor released by SONY is the ability of the sensor’s PD diodes to focus quickly and accurately even in poor light.

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