Analysis, Enhancement, and Sensitivity Improvement of the Correlation Image Sensor

The correlation image sensor (CIS) is used in a variety of applications which involve the extraction and measurement of low-amplitude-modulated light signals from background interferences. Many applications have been reported on measurement of ac magnetic flux, interferometry, eye gaze tracking, and indirect 3-D imaging using these sensors. In this paper, the performance of different derivatives of the CIS is analyzed, and some modification is applied to the CIS to significantly increase its sensitivity at higher frame rates and reduce its output error. The effect of undesired parameters, such as parasitic capacitances, device mismatches, charge transfers, random noise, and temperature variations, is studied, and modified architectures are proposed to reduce them. The maximum demodulation frequency is also shown to be increased compared to original CIS. The presented designs are compared with previous solutions under similar operating conditions using a 0.35-mu m standard CMOS technology. It is shown that the designs can be used to detect lower modulated signal levels over a wider background dynamic range.