We propose a CMOS image sensor which can capture both whole images at 60 fps and several region-of-interests (ROIs) images at a high-speed frame rate of 2.1 kfps. We have designed a sensor prototype for our newly developed man-machine interface system called “Opto-Navigation”. In the system, LEDs as optical beacons are equipped with portable devices such as mobile phones and digital cameras, and provide a useful guide for visually aided data communication with them. The optical beacons inform their positions at slow frequency around 10 Hz, which define ROIs, and send their ID data with bit rate of 1kbps to the sensor. The sensor can recognize the position of IDs with frame differences of 60-fps images and then obtain the ID data by reading only ROIs at high frame rate. Thus by using the image sensor a user can know what devices can be communicated with and select one of them to send/receive information data. A QVGA image sensor dedicated for the “Opto-Navi” system has been fabricated in a 0.35-μm 2-poly 3-metal standard CMOS technology. The pixel has 7.5 × 7.5 μm2 area with a fill factor of 24.9%.
A frequency-demodulation CMOS image sensor for capturing images only by the modulated light is proposed and demonstrated. The pixel circuit has two FD (floating diffusion) for accumulating signal charges and one photo-gate for detecting the modulated light and the background light. By operating the image sensor synchronously with a frequency and a phase of the modulated light, signal charges generated by the modulated light and the background light are accumulated at FD of one side, while signal charges generated only by the background light are accumulated at another FD, respectively. By subtracting outputs of two FD with the off-chip subtraction circuits, images produced only by the modulated light can be obtained.
Based on the proposed circuit, an image sensor with 64 × 64 pixels are fabricated by using 0.6 μm CMOS technology. We captured images by using this image sensor and demonstrate the sensor can capture images only by the modulated light. When the object is partially illuminated by the modulated illumination under constant background illumination, we can successfully demonstrate the image sensor captures the potion illuminated by the modulated light with removing any static background light. Also we demonstrate the marker detection. When the marker is attached to an object under several background illuminations, the image sensor can extract the marker without affected by the background illumination intensities. A motion capturing is successfully demonstrated by use of this sensor.