The Research And Chip Implementation Of CMOS-TDI Image Sensors

Time-Delay-Integration (TDI) image sensor is a kind of special line array visualsensor. Under the condition of high scanning speed, TDI image sensor can get highersignal-to-noise ratio and sensitivity comparing to the traditional line array imagesensor, so it is especially suitable for application in space imaging, medical imaging,industrial detection and etc. As the scaling of CMOS process technology andincreasing of the circuit integration, the TDI image sensor based on standard CMOSprocess technology becomes a very popular research issue. Therefore, based on theresearches of system architecture and readout circuit design of analog and digitaldomain CMOS-TDI image sensor, this thesis will carry out the research and chipimplementation of CMOS-TDI image sensor.Based on the in-depth analysis of the current researches in CMOS-TDI imagesensor, two CMOS-TDI image sensor architectures which can achieve signalaccumulating in analog domain and digital domain respectively are proposed in thisthesis. An analog accumulator for analog domain CMOS-TDI image sensor isproposed, and the parasitic phenomenon in the analog accumulator is also analyzed,and two methods for overcoming this phenomenon are proposed. Two kinds ofcolumn parallel analog-to-digital converter (ADC) are proposed for digital domainCMOS-TDI image sensor. One is a Cyclic ADC with analog signal pre-processingfunction, and the other one is a capacitor mismatch insensitive Cyclic ADC withoffset canceling. Several methods for combating the IR-drop and clock drivingproblems in long line array image sensor are also proposed in this thesis. In this thesis,the whole designs of analog and digital domain CMOS-TDI image sensor arecompleted through theoretical analysis, system modeling and circuit simulation, andtheir prototype chips have been fabricated through GSMC0.18μm CMOS technology.The experimental results indicate that the proposed readout circuits work effectivelyand can satisfy the requirement of128-stage CMOS-TDI image sensor with a lengthof1024pixels and a line rate of3875lines/s.The creative works of the thesis include:1. An analog accumulator for analog domain CMOS-TDI image sensor isproposed. OPA sharing and input-referred offset storing technologies are applied inthe proposed accumulator, which result in less chip area and power consumption and lower column FPN. With CDS operation, the proposed accumulator reduces thereadout noise introduced by pixels. The parasitic phenomenon in the analogaccumulator is overcome by decoupling capacitor, which makes accumulator withhigher stage realizable.2. A dynamic current source with immunity from IR-drop is proposed. Theproposed current source clamps the gate-source voltage of traditional current sourceand reduces the impact of IR-drop on the current provided by the current source. Theproblem of current providing in the pixels and readout circuits of long arrayCMOS-TDI image sensor is solved by the proposed current source.3. A ratio-insensitive MDAC with offset canceling is proposed. The proposedMDAC reduces the impact of capacitor mismatch on the linearity of Cyclic ADC, andtherefore the requirement of circuit design is relaxed and the conversion resolution ofthe Cyclic ADC is improved. The Cyclic ADC with the proposed MDAC is verysuitable for application in digital domain CMOS-TDI image sensor.