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 5.6μm and decayed by 90° 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 0.1mm2 and consume 24μW 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 5μm. 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 5μm was
measured.
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.
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