The products in the market are mostly 2D sensing. The touch panel technology is used in the industry and the video game wisely. Many of the ATMs, cell phones and the vending machines have touch panel technology in these years. The touch panel technology grows up quickly. In recent years, there has been increasing interests in proximity sensing technology [1–3]. This study proposes the 3D proximity sensing can be used in un-touch screen, a 3D keyboard, or constructed on the robot’s hand for sensing the distance and position of an object. As the optical components advance, the optical system, optical touch panel, object sensing and medical system are growing up with it. A photo detector is the part of the optical component. However, the photo detector transfers the photon to the current (photocurrent). This study needs a circuit to be the rear end of the photo detector, transferring the current to the voltage. An active pixel sensor is the viable way to realize the function. For the large area object sensing and high resolution, one pixel should be designed as small as possible. A small pixel however gives small photocurrent. The efficient way to transfer the photon to the voltage is important. The aim of this study is to develop a 3D-position sensing technique for an arbitrary object. The schematic for illustration is shown in Fig. 1. Different from conventional 2D capacitance or resistance touch panels, the proposed proximity sensor array has third axis sensing and the 3D sensing. A new active pixel circuit is proposed for realizing the sensor array. The active pixel sensor is used to convert the light to the voltage, and it can improve the resolution and reduce the noise. The standard and official active pixel sensor is a 3T-structure APS (or 3T-APS). The drawback of 3T-APS is that the output range is limited by the original circuit design. The maximum output cannot be up to bias voltage. The new APS resolution is better than the standard 3T-APS resolution in this aspect. It is a good improvement in terms of not only the CMOS sensor but also the 3D optical proximity sensing circuit.
