A Polar Symmetric CMOS Image Sensor for Rotation Invariant Measurement

We present a CMOS image sensor for efficient capture of polar symmetric imaging targets. The array uses circular photodiodes, arranged in concentric rings to capture, for example, diffraction patterns generated by optically probing a revolving MEMS device. The chip is designed with a vacant, central spot to facilitate the easy single-axis alignment of the probing illumination, target device, and detector. Imaging of high-speed rotation (>1 kfps) is made possible by dividing the array into multiple concentric bands with sectorwise addressing control. We introduce a global shutter pixel reset scheme that reduces fixed pattern noise by being insensitive to parasitic capacitance from variable routing. We demonstrate the sensor's capability to measure the rotation angle with a precision of 32 μ rad and the rotation rates up to 300 rpm. Finally, we demonstrate the concept of a compact optical metrology system for continuous inertial sensor calibration by imaging the diffraction pattern created by a commercial MEMS accelerometer probed by a red laser shone through the axis of symmetry of the image sensor.