- 學位論文
應用於自動對焦系統之CMOS霍爾效應磁場感測器
Design of a CMOS Hall Effect Sensor for Auto Focus System Application
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摘要
磁場感測器應用於許多商用產品以及工業環境之中。而其中霍爾效應感測器因能整合於CMOS晶片製程，所以有相當高的普遍性。雖然霍爾效應感測器的成本較低，但由於其靈敏度較差，故早期主要應用於較大磁場範圍的感測，像是感測馬達風扇周邊的磁場或是電流。隨著CMOS製程和電路設計的進步，加上消費性電子產品蔚為風潮，霍爾效應感測器開始逐漸應用於更微弱的磁場訊號感測。舉例來說，iPhone手機當中的電子羅盤即為霍爾效應感測器實現而成。 霍爾效應感測元件可等同於惠斯同電橋結構。因為製程飄移的因素，所以等效惠斯同電橋之四個電阻值會不匹配。此非理想效應在本論文中使用旋轉電流技術來去除其對系統的影響。另外，前端放大器不匹配所造成的偏移電位以及伴隨的低頻閃爍雜訊，採用截波器的調變技術將其去除。前端放大器的架構採用電容回授式儀表放大器，此架構相較於電流回授式儀表放大器在同樣功率下能夠達到較低的雜訊。本論文還有採取T型電容網絡架構使輸入以及回授電容可以有效的節省86%的電容面積。前端放大器的偏移電位因會在輸出產生三角波的漣波，本論文使用交流耦合漣波抑制電路來克服這個問題。 此磁場感測器實作於台積電0.18微米CMOS製程。晶片核心面積為0.13平方毫米，在1.8伏特的電源下消耗160微安培的電流，並達到頻寬為174千赫茲且雜訊為每根號赫茲下有26.5奈伏特的表現。在磁場表現部分，給予正負400毫特斯拉的狀況下，線性度小於0.5%的誤差之內。磁場感測電路之等效輸入偏移小於100微特斯拉。在磁場輸入為正負100毫特斯拉的範圍下可以達到約為10個位元的解析度。
並列摘要
Magnetic field sensor is widely used in commercial products and industry environment. Because Hall effect sensor can be integrated in CMOS process, it is applied in many systems. Although the cost of Hall effect sensor is lower, its sensitivity is poorer that its early applications is mostly for larger magnetic field strength. For example, sensing magnetic field strength or current around the fan of motor. With the advance of CMOS process and circuit design, Hall effect sensor begins to sense weaker magnetic field for consumer electronics. For instance, electronic compass in iPhone is implemented with Hall effect sensor. Hall effect sensing cell can be modeled as a Wheatstone bridge. Because of the process variation, the four resistor value of Wheatstone bridge will not be the same. This thesis presents spinning-current technique to solve this non-ideality. With chopper modulation technique, the offset caused by the transistor mismatch of the amplifier and the flicker noise of the transistor can be resolved. The architecture of the analog front end is capacitively-coupled instrumentation amplifier (CCIA); it achieves lower noise than that of a current-feedback instrumentation amplifier (CFIA) in the same power dissipation. The thesis also presents a T-capacitor network that saves 86% capacitor area of input and feedback capacitor. The offset from transistor mismatch will cause the triangle output ripple, so ac-coupled ripple reduction loop (RRL) is presented to overcome this problem. The magnetic field sensor is fabricated in TSMC 0.18-μm CMOS process. The core area is 0.13 mm2 and current dissipation is 160 μA from a 1.8-volt supply voltage. It achieves 174-kHz bandwidth and input-referred noise is 26.5 nV /√Hz. The linearity is better than 0.5% within ±400 mT magnetic field strength. The input-referred offset is smaller than 100 μT. Its resolution is 10 bits when applying ±100 mT magnetic field strength.
參考文獻
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