A 100mK-NETD 100ms-startup-time 80×60 micro-bolometer CMOS thermal imager integrated with a 0.234mm²1.89μV<inf>rms</inf> noise 12b biasing DAC

Abstract

A micro-bolometer focal plane array (MBFPA) detector is one of the best candidates for thermal imaging cameras due to its excellent uncooled imaging performance with low manufacturing cost [1-4]. In Fig. 10.8.1, remote infra-red signals from thermal objects are maximized and absorbed at the MEMS micro-bolometer pixels having a λ/4 cavity structure, and they are then converted into resistance of a thermistor layer in each cell. Then, a CMOS analog front-end (AFE) reads out the cell resistance value in current-mode by applying a voltage bias to the micro-bolometer pixel. In the readout process, the skimming cell that does not respond to the infra-red signal is used to remove the offset components by generating an opposite-phase current, which in turn alleviates the system required resolution. Nevertheless, there is still very significant fixed-pattern noise (FPN) resulting from process, voltage, and temperature (PVT) variations, and this severely limits the responsivity/dynamic range trade-off. Addressing the problem, both bias voltages (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">FID</sub> & V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">GSK</sub> ) applied to sensing and skimming cells, respectively, should be precisely adjusted so as to avoid any saturation while maintaining sufficient responsivity, and their noise levels must be low enough considering the noise amplification in the signal chain.