Abstract
This article presents a color light detection system integrated in 130 nm CMOS technology. The sensors and corresponding electronics detect light in a CIE XYZ color luminosity space using on-chip integrated sensors without any additional process steps, high-resolution analog-to-digital converter, and dedicated DSP algorithm. The sensor consists of a set of laterally arranged integrated photodiodes that are partly covered by metal, where color separation between the photodiodes is achieved by lateral carrier diffusion together with wavelength-dependent absorption. A high resolution, hybrid, ∑∆ ADC converts each photo diode’s current into a 22-bit digital result, canceling the dark current of the photo diodes. The digital results are further processed by the DSP, which calculates normalized XYZ or RGB color and intensity parameters using linear transformations of the three photo diode responses by multiplication of the data with a transformation matrix, where the coefficients are extracted by training in combination with a pseudo-inverse operation and the least-mean square approximation. The sensor system detects the color light parameters with 22-bit accuracy, consumes less than 60 μA on average at 10 readings per second, and occupies approx. 0.8 mm2 of silicon area (including three photodiodes and the analog part of the ADC). The DSP is currently implemented on FPGA.
Highlights
Colorimetric light measurements are typically based on three independent optical sensors with a defined spectral responsivity behavior that matches the CIE color matching functions (CMF) [1].Different color matching functions like R, G, B or X, Y, Z were defined by experiments and empirical observation according to the human eye’s color perception
An integrated CMOS color sensor based on lateral carrier diffusion is realized in 130 nm CMOS technology without any process modification, and together with a high resolution
analog to digital converter (ADC) and digital color signal processing is described in this article
Summary
Colorimetric light measurements are typically based on three independent optical sensors with a defined spectral responsivity behavior that matches the CIE color matching functions (CMF) [1]. A sensor in a low-cost technology without triple-well and process modification, but only with optimization of the spectral sensor response by layout modifications is proposed in this paper. Another method for tuning the sensors response, based on the generation of high electric fields in a widely depleted epitaxial layer of a CMOS technology, is reported in [10,11]. In order to avoid filters and expensive multi-diode stacks, the proposed color detection methods are based on wavelength-dependent light absorption, together with lateral carrier diffusion effects and complex analog and digital signal processing.
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