Advanced circuit architectures for readout electronics of low-cost microbolometer focal plane arrays

Çöloğlu, Mustafa Haluk
This thesis presents a study on the design and characterization of advanced circuit architectures for readout electronics of low-cost microbolometer focal plane arrays (FPAs). In this respect, two advanced circuit architectures are developed in order to improve the performance, flexibility, and simplicity of use of the microbolometer based low-cost thermal imaging sensors. The first circuit architecture is developed for the readout electronics of 40x40 focal plane array (FPA) with 60 µm pixel pitch using 0.35 µm CMOS technology and contains several digital circuit blocks such as a digital controller, row scanner, column multiplexer, serial peripheral interface (SPI), sensor configuration memory, and pixel level biasing (PLB) memory assigned to the selected FPA row. The digital controller block allows the sensor to generate its own timing signals using only an external clock signal. The row scanner performs a selection of single FPA row at a time and the column multiplexer serializes the analog outputs of the column readout channels. A standard 4-wire SPI is designed to provide a simple communication means between the sensor memory and external controller. This programmability provides flexible operation under different conditions. The designed circuit blocks in the first sensor were tested and verified, then, first infrared images were obtained from the sensor. In order to improve the sensor performance, a simple but very efficient detector bias calibration algorithm is developed on Field-ProgrammableGate-Array (FPGA). The test results of the developed algorithm show that the effects of all non-uniformity sources can be compensated in just 7 frames with simple camera electronics. The second circuit architecture is developed for the readout electronics of 80x80 FPA with 35 µm pixel pitch using 0.18 µm CMOS technology. Besides the circuit blocks developed for the first sensor, the second circuit architecture has several important improvements. Firstly, the PLB memory of the second sensor is designed to store the calibration data of all pixels. This improvement simplifies the physical interface between the sensor and camera electronics, since no real time data transmission is required to fill PLB memory. Secondly, the detector bias calibration algorithm developed for the first sensor is integrated into the second sensor. Thanks to this improvement, the second sensor is able to self-calibrate itself by using only on-chip components. Lastly, the image windowing feature, which may be required in some applications to decrease total power consumption of the sensor by reducing the resolution of the output image, is added to the second sensor. The circuit architectures developed in the scope of this thesis can be used for all types of microbolometer FPAs to improve their performance. The developed circuit architecture for the second sensor makes it the first thermal imaging sensor having fully on-chip non-uniformity correction feature in Turkey.