Pixelwise readout integrated circuits with pixel-level ADC for microbolometers

C. H. Hwang; C. B. Kim; Y. S. Lee; B. G. Yu; H. C. Lee

doi:10.1117/12.719155

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14 May 2007 Pixelwise readout integrated circuits with pixel-level ADC for microbolometers

C. H. Hwang; C. B. Kim; Y. S. Lee; B. G. Yu; H. C. Lee

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Proceedings Volume 6542, Infrared Technology and Applications XXXIII; 654221 (2007) https://doi.org/10.1117/12.719155
Event: Defense and Security Symposium, 2007, Orlando, Florida, United States

Abstract

Pixelwise integrated circuits involving a pixel-level analog-to-digital converter (ADC) are studied for 320 × 240 microbolometer focal plane arrays (FPAs). It is necessary to use the pixelwise readout architecture for decreasing the thermal noise. However, it is hard to locate a sufficiently large integration capacitor in a unit pixel of FPAs because of the area limitation. To effectively overcome this problem, a two step integration method is proposed. First, after integrating the current of the microbolometer for 32&mgr;s, upper 5bits of the 13bit digital signal are output through a pixel-level ADC. Then, the current of the microbolometer is integrated during 1ms after the skimming current correction using upper 5bits in a field-programmable gate array (FPGA), and then lower 8bits are obtained through a pixel-level ADC. Finally, upper 5bits and lower 8bits are combined into the digital image signal after the gain and offset correction in digital signal processor (DSP) Each 2×2 pixel shares an readout circuit, including a current-mode background skimming circuit, an operational amplifier(op-Amp), an integration capacitor and a single slope ADC. When the current of a microbolometer is integrated, the integration capacitor is connected between a negative input and an output of the op-Amp. Therefore a capacitive transimpedance amplifier (CTIA) has been employed as the input circuit of the microbolometer. When the output of a microbolometer is converted to digital signal, the Op-Amp is used as a comparator of the single slope ADC. This readout circuit is designed to achieve 35×35&mgr;m² pixel size in 0.35&mgr;m 2-poly 3-metal CMOS technology.

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C. H. Hwang, C. B. Kim, Y. S. Lee, B. G. Yu, and H. C. Lee "Pixelwise readout integrated circuits with pixel-level ADC for microbolometers", Proc. SPIE 6542, Infrared Technology and Applications XXXIII, 654221 (14 May 2007); https://doi.org/10.1117/12.719155

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