Realization of readout integrated circuit (ROIC) for an array of 288x4, N-on-P type HgCdTe long wave infrared detectors

Official URL: http://192.168.1.20/record=b1266174 (Table of Contents)

Infrared (IR) imaging systems are used in a variety of applications from biomedical to astronomic and strategic imaging. Modern military missile guidance and surveillance systems also incorporate infrared imaging systems. The most critical component of an infrared imaging system is the focal plane array (FPA), a key assembly of detectors and readout electronics to carry out the function of infrared to electrical signal conversion. As in all sensor networks, extraordinary care must be given to both the detector design and readout integrated circuits, to obtain a high performance and durable system. In IRFPAs, detectors set the operation wavelength, readout circuit area and operation temperature. However many of the system performance parameters such as signal to noise ratio (SNR), linearity, input referred noise level, dynamic range, are set by the readout integrated circuit (ROIC). First generation of IR imaging systems incorporated single detector, or a fewer number of detectors. Higher frame rate and resolution requirements brought up the scanning type of FPAs where a scene is scanned constantly to create a 2D electronic image by a single array of detectors. Scanning type FPAs, with higher frame rates, started to replace staring arrays, with the maturing of detector processing technology and allowing integration of thousands of functioning detectors (pixels) on a single substrate, with smaller pitches. However, scanning type arrays are attractive due to their lower cost. In this thesis, design of a CMOS readout integrated circuit for an array of 288x4, n-on-p type HgCdTe long wave infrared detectors is presented. ROIC input preamplifier is current mirroring integration type due to low input impedance requirement. In order to increase SNR, time delay integration (TDI) on 4 detectors is applied with a super sampling rate of 3. ROIC has additional features of bidirectional TDI scanning, dead pixel deselection, automatic gain adjustment in response to pixel deselection, in addition to programmable four gain settings (up to 2.58pC storage), and programmable integration time. ROIC has four outputs with a dynamic range of 2.8V (from 1.7V to 4.5V) and input referred noise of 2989 electrons for an area of 13mm2. Two clocks: master clock and integration clock are required in order to operate the ROIC. Integration clock sets the integration time and adjust frame rate. Master clock maintains synchronization and can be adjusted up to 5MHz. ROIC can be programmed through both serial and parallel interface with full functionality but pixel deselection being allowed only in serial interface mode.