(A) study on improvement of noise characteristic and dynamic range of readout integrated circuit for infrared focal plane arrays

Abstract

In this study, the readout circuit which improves signal to noise ratio and dynamic range was discussed for 2-D LWIR applications. Firstly, the two-step background suppression method was proposed to improve the signal to noise ratio for normal applications of LWIR FPAs. Secondly, the smart reset control method was introduced to improve the dynamic range for various applications of LWIR FPAs. Finally, new pixel level ADC was proposed to improve both the signal to noise ratio and dynamic range, and it realize the optimum solution of on-chip ADC for LWIR FPAs. Using these methods, we can obtain the high performance IR image. Though these methods are optimized for LWIR applications, they can be used for MWIR or visible ray. In the readout circuit design for an infrared focal plane array, noise performance is a very important concern. Especially in LWIR applications, the improvement in SNR is proportional to the square root of the integration time. Therefore, it is necessary to use a large integration capacitor for long integration time. However, in a 2-D application, it is hard to locate a large integration capacitor in the pixel because of area limitation. To make matters worse, a LWIR HgCdTe detector has a large background current compared to its signal current in normal applications. To effectively overcome these problems, a current mode background suppression technique can be used. However, the previous designs are not available for 2-D LWIR applications because of large skimming error and refresh noise. To overcome these drawbacks, we proposed a novel readout circuit involving a two step current mode background suppression method. This method can effectively increase the SNR of image data because of its low noise characteristics. The readout circuit is expected to offer very small skimming error (<0.3 %) and long integration time (>2 ms) for an adequate calibration range. In the normal applications where the target is far from detector and the target temperatu...