Experimental Characterization of a CMOS Pixel with a Tunable Color Space

The Transverse Field Detector (TFD) is a pixel device proposed for imaging without color filters. Color separation is obtained with a suitable generation of transverse electric fields in a semiconductor single depleted region and is based on the Silicon absorption properties. Thanks to this working principle, this device has a unique characteristic to have an electrically tunable native color space. In this paper we review the operation of color devices based on the Silicon absorption properties, then we focus on the potential advantages of the TFD with respect to previous solutions. We present opto-electrical experimental measurements on the characterization of a prototype, and we suggest and simulate a re-designed structure that can improve the device color detection capabilities. We then propose a dual use of the TFD: in "standard imaging" mode it can achieve performance comparable to those of commercial cameras (in terms of mean color reconstruction error and color conversion matrix coefficients); in "high color accuracy (HCA)" mode it can achieve optimum color reproduction (mean Delta E-a,E-b = 0.3 for the Macbeth Color Checker). This result is obtained simply through three consecutive image acquisitions with electrical tunings of the device color space.