Date

2016

Author

Yalçın, Cem

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This thesis presents a small format Readout Integrated Circuit (ROIC) for surface micromachined resistive microbolometer imaging sensors. The imaging sensor is designed to work in the Long Wave Infrared region (8 – 14 um) and is designed with an 80 x80 format with a pixel pitch of 25 um. The ROIC is optimized to perform the readout of MEMS pixels with resistance values around 60 Kohm, where infrared blind reference resistors with similar values are also used to cancel effects of selfheating and high biasing current. The ROIC is capable of performing Non-Uniformity Correction on the detectors with a resolution of 8 bits, allowing the readout of a wide range of resistance values. The ROIC utilizes a panel-based approach for imaging, dividing the pixel array into 9 blocks for reducing the die size of the ROIC, which is required to reduce the cost of the infrared imager. The circuit also has a Successive Approximation Register (SAR) Analog-to-Digital Converter (ADC) to convert analog readout signals to digital data for better noise performance, lower system power, and smaller system size. The ADC has 12 bits and 62.5 kS/s sample rate. The circuit is designed to achieve imaging at or below 9 Hz while consuming a low power of 65 mW and providing a Noise Equivalent Temperature Difference (NETD) of 50 mK, which is comparable with the state-of-the-art microbolometers. The readout IC generates its own timing and biasing signals. Its external pins are composed of power pins and digital communication pins, easing system integration. Timing signals are generated by a digital controller and are very flexible. A bias generator implemented in the ROIC contains various voltage and current DACs to generate necessary biasing signals for the circuit, utilizing a bandgap reference voltage generator. Both the timing and biasing signals are configured through the configuration memory of the ROIC, which can be accessed through a simple serial programming interface. Reference resistor selection circuits located in columns allows the user to disable any faulty reference pixel in the array arbitrarily, without affecting the operation of other readout columns. CMOS resistors located in the pixel array extend test coverage before MEMS processing. These resistors can also be used as reference resistors in the case of high disparity between MEMS reference and detector resistors. A layout of the ROIC is implemented using a 0.35 m CMOS process. A 6mm x 6mm sized design was sent to multi-project wafer (MPW) fabrication for the verification of the operation. A full engineering run is required to achieve MEMS processing and to demonstrate imaging. 

Subject Keywords

Microbolometers., Infrared imaging., Infrared technology., Analog-to-digital converters.

URI

http://etd.lib.metu.edu.tr/upload/12620453/index.pdf 
https://hdl.handle.net/11511/25952

Collections

Graduate School of Natural and Applied Sciences, Thesis