應用於氣體感測系統之具直流光電流抵銷功能之類比前端轉阻放大器

An Analog Front-End Transimpedance Amplifier with DC Photocurrent Cancellation for Gas Sensing Applications

林登凱(Deng-Kai Lin)

指導教授 ： 林宗賢

國立臺灣大學/電機資訊學院/電子工程學研究所/碩士(2018年)

https://doi.org/10.6342/NTU201803103

摘要

本論文實現了與氣體感測應用相關的類比前端放大電路設計。在一個氣體感測微系統中，類比前端電路是最重要的電路部分，因為它必須在大的外界雜訊干擾下，將微弱的訊號放大並送給後級電路處理。一個實作在PCB板上的原型電路以及一個實作在晶片上的前端轉阻放大電路皆被實現出來與驗證。
第一個作品是一個具有自動校正功能的兩級轉阻放大器。藉由使用電池做為參考電壓源，並將電路頻寬限制在一赫茲，可將電路雜訊造成的影響降至最低。電路的自動校正是透過微控制器的數位控制方式來實現。此轉阻放大器被整合在一個可攜式的二氧化碳偵測裝置中，該裝置藉由計算在不同二氧化碳濃度下產生電壓變化的斜率，來得知當下的氣體濃度。實驗結果顯示它最低可偵測到百分之四的二氧化碳濃度。
第二個作品是一個具有直流光電流抵銷功能的類比前端轉阻放大器。此電路加入了截波技巧以降低放大器的偏移電壓與閃爍雜訊所造成的影響。電路輸入端的大直流光電流由一數位校正迴路來消除，以增加電路的輸出動態範圍。本晶片使用聯電零點一八微米製程來實現。核心面積為零點二八平方毫米，在不開啟電流式數位類比轉換器時，在一點八伏特的供應電壓下總消耗功率為零點六七毫瓦。該電路在不開啟電流式數位類比轉換器的情況下，在一千赫茲的頻寬下可達到六十二點四分貝的訊號雜訊比。實驗結果說明了將本電路整合進二氧化碳偵測系統的可行性，並實現百萬分之五十的偵測解析度。

關鍵字

類比前端電路 ； 轉阻放大器 ； 氣體感測系統 ； 截波 ； 直流光電流抵銷

並列摘要

This thesis presents the design of analog front-end (AFE) circuits for gas sensing applications. In a gas sensing microsystem, the AFE circuit is the most critical building block, since it must amplify weak signal in the presence of large interferences. A PCB prototype circuit and an on-chip front-end TIA circuit are implemented and verified.
The first work is a two-stage transimpedance amplifier with auto-calibration. The noise of circuit is minimized by using batteries as voltage source and limiting circuit bandwidth to 1 Hz. The auto-calibration of the TIA is realized by digital control from the microcontroller. A portable CO2 detection device is constructed with the TIA integrated-in, and the slopes of voltage change under different concentrations of CO2 are calculated to extract the gas concentration. It demonstrates a minimum detection concentration of 4%.
The second work presents an analog front-end transimpedance amplifier with DC photocurrent cancellation. Chopping technique is utilized in this work to reduce the effect of amplifier offset and flicker noise. A digital calibration loop is implemented to cancel the large DC photocurrent and increase the detection dynamic range. The chip is fabricated with UMC 0.18-μm CMOS process. The core area is 0.28 mm2 and it consumes 0.67 mW from 1.8-V supply when the current DAC is disabled. It achieves a SNR of 62.4 dB under 1-kHz bandwidth with the current DAC disabled. The results prove the feasibility to integrate this circuit in a CO2 detection system, achieving detection resolution of 50 ppm.

並列關鍵字

Analog Front-End Circuits ； Transimpedance Amplifier ； Gas Sensing System ； Chopping ； DC Photocurrent Cancellation

參考文獻

References

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[3] D. Gibson and C. MacGregor, "A Novel Solid State Non-Dispersive Infrared CO₂ Gas Sensor Compatible with Wireless and Portable Deployment," Sensors, pp. 7079-7103, May 2013.

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