(A)CMOS Image Sensor Acquiring Fingerprint Pattern with 1-bit Resolution for Pointing Device Applications

다국어 초록 (Multilingual Abstract)

As digital convergence that includes a variety of applications in a single mobile device was realized, a pointing device for mobile devices has become an important research area. Among various pointing devices, the optical finger navigator is based on the motion of fingerprint images. It measures change in position by processing the fingerprint image data received from an image acquisition system. Thus, a CMOS image sensor is very important system in the optical finger navigator. In addition, low power consumption and small chip area are the key issues in the design.
This paper describes a CMOS Image Sensor (CIS) that acquires the fingerprint pattern generated by ridges and valleys of the finger for the optical finger navigator. In order to reduce the amount of calculation in the digital back-end that performs the motion vector estimation, the proposed CIS acquires the fingerprint pattern using only 1-bit image data. However, the proposed CIS leads to lower image quality compared to general CMOS imagers. To mitigate this weakness, it has a reference voltage controller, which adjusts a reference voltage to the optimal level to distinguish between ridge images and valley images of the fingerprint accurately. And the reference voltage is controlled automatically by Successive Approximation Register (SAR) structure. As a result, the proposed CIS can acquire the accurate fingerprint pattern without losing the image integrity.
The proposed CIS is fabricated in a standard 0.5um 1-Poly 3-Metal CMOS process. The pixel array has 30×30 pixels with the unit pixel size of 30um×30um. The core size of CIS is 1.65mm×1.45mm and the power consumption is about 500uW at 3.3V power supply.

목차 (Table of Contents)

• Table of Contents
• Abstract i
• Table of Contents iii
• List of Figures iv
• List of Table vi
• 1 Introduction 1
• 1.1 Motivation 1
• 1.2 Contents 3
• 1.3 Organization 4
• 2 Solid State Image Sensors 5
• 2.1 Backgrounds 5
• 2.2 Charge-coupled device (CCD) Imagers 7
• 2.3 CMOS based Imagers 10
• 2.3.1 Passive CMOS image sensors 11
• 2.3.2 Active pixel sensors 13
• 2.4 Comparison of CCD and CMOS imagers 19
• 2.5 Trends in CMOS image sensors 21
• 3 1-bit Fingerprint Pattern 24
• 3.1 Proposed algorithm 24
• 3.2 Motion Detection Pointing Device 28
• 4 1-bit CMOS Image Sensor Design 30
• 4.1 Architecture 30
• 4.2 Building Blocks 32
• 4.2.1 Photodiode 32
• 4.2.2 3-tr Active Pixel Sensor 35
• 4.2.3 Correlated Double Sampling 36
• 4.2.4 Voltage Comparator 38
• 4.2.5 Timing Blocks 39
• 4.2.6 Automatic Reference Voltage Controller 40
• 5 Experiment Results 46
• 5.1 Simulation Results 46
• 5.1.1 Pixel 46
• 5.1.2 Row decoder and Column decoder 47
• 5.1.3 Successive Approximation Register 48
• 5.1.4 Resistor string DAC 50
• 5.1.5 Full Simulation 51
• 5.2 Layout 52
• 5.3 Test Results 53
• 5.4 Comparisons 55
• 6 Conclusion 56
• REFERENCE 58