A speckle-based CMOS sensor array for arbitrary surface movement detection

The paper presents a CMOS sensor array for the detection of speckle movements, for applications requiring accurate movement tracking of arbitrary surfaces. The array is made of eight sensors incorporating each a spatial comb filter with a pitch of 2.8μm so as to be direction-sensitive to the movement of speckles with corresponding direction and spatial frequency, defined by the optical geometry of the system. The circuit is used with an array of micro-lenses placed between the sensor and the laser-illuminated surface. With speckle statistics (contrast, size) being independent on the surface properties, the detection works on virtually any surface. The system is operated at a sampling frequency of 64kHz. Integrated into a 180nm CMOS process, the circuit active area occupies 1.9mm2 and consumes 290μW at full speed, allowing a maximal stable tracking speed of the surface of 0.25 m/s and a tracking accuracy of about 5μm.