(A) study on smart readout integrated circuit for improvement of image quality of infrared image sensors

Abstract

In this dissertation, the two types of smart readout integrated circuits (ROICs) for the infrared image sensors are discussed. The smart readout integrated circuits have not only basic function of conventional circuit but also active functions to solve some problems in short wavelength infrared (SWIR) and long wavelength infrared (LWIR). This dissertation consists of the two parts in which each of the smart readout integrated circuits is explained one by one. Infrared bands including SWIR, MWIR, and LWIR have different characteristics. Dominant source of SWIR which is located near visible band is the reflected IR from the object. Thus, it is strongly dependent on light source such as sun or moon, which makes the large gap in light intensity between day and night. For this reason, dynamic range is big issues in SWIR camera system, and it has been researched actively. In this study, three techniques which are pixel-level ADC, signal current adaptive integration time, and self-controlled integration capacitance are proposed and applied to readout circuit for SWIR detector array. New readout circuit with the proposed techniques can automatically control the integration time and capacitor in each pixel individually, which makes the camera have wide dynamic range. Also, low noise and simple system design are possible by the pixel-level ADC. The fabricated readout integrated circuit has 140 dB dynamic range with good signal-to-noise ratio (SNR). In LWIR camera markets recently, the prime consideration is the low cost, low power consumption, and low volume. The resistive bolometer which are the representative LWIR image sensor suffers from the spatial noise. To solve this problems, thermo-electric cooler (TEC) has been used. However, TEC increases power consumption, volume, and cost. Thus, TEC-less system which allow microbolometer arrays to operate without temperature stabilization is required to keep pace with rapid changes in the market. In this study, new TEC-less readout integrated circuit with self-bias equalization method is proposed. The new TEC-less readout integrated circuit can check the non-uniformity in each pixel by itself and find the bias voltage for correction. The fabricated readout integrated circuit has non-uniformity value under 50mK NETD for -20 ~ 70$^o$C.