A speckle-based CMOS sensor for arbitrary surface movement detection with correlated double sampling and gain error correction
We present a CMOS sensor for accurate tracking of speckle movements on arbitrary surfaces. The sensor is made of a pair of comb filters with a pitch of 5.6 mu m and decayed by 90 degrees to produce quadrature signals. The readout circuit is a 60 dB amplification chain with offset and KTC noise compensation. Integrated into a 180nm CMOS process, the sensor and readout circuit occupy an area of about 0.1 mm(2) and consume 24 mu W at full speed of 64 ksample/s. The direction and frequency of the quadrature signals are resolved externally by zero- crossing detection, giving an accuracy of about 5 mu m. Thanks to a careful layout for gain error minimization, and the use of KTC noise cancellation, a negligible residual drift was observed, and a minimal displacement of 5 mu m was measured.