心電圖儀中57Hz低通橢圓濾波電路設計

57Hz Low Pass Elliptic Filter Circuit Design of ECG

林展輝(Chan-Hui Lin)

指導教授 ： 張俊明

中原大學/工學院/電機工程研究所/碩士(2011年)

https://doi.org/10.6840/cycu201100651

摘要

摘要
在類比濾波電路設計領域上，首要重視的就是輸出訊號的準確度，使輸出訊號準確的操作在預定的頻率範圍之內，為設計電路第一目標。心電圖儀監測設備，是擷取人體非常微弱的生理訊號，輸出的訊號準確度經常受到測試環境與設備因素而影響。濾波電路設計，輸出訊號的準確度就是首要的重要研究。
運算轉導放大器(Operational Transconductance Amplifier，簡稱OTA)是目前類比電路設計是近年來學者公認最佳的主動元件，其特性為 ， 為輸出電流， 為正端輸入電壓， 為負端輸入電壓， 為轉導增益值，輸入電流I+=I-=0。OTA的轉導增益值，代表輸出電流 與差動電壓 的比值，而 值可藉由調整偏壓電流 來控。國際有學者提出OTA-C電路分析合成設計法，此OTA-C濾波器電路有四個優良特點，(1)轉導值 可調整 (2)工作頻寬範圍較大 (3)輸入阻抗大，較易於與其他電路串接 (4)使用最少的主、被動元件，使電路的寄生效應降至最低，進而大幅提升電路輸出訊號的準確度。電路推導的部分，根據分析合成設計法，利用節點分析法來設計電路，轉移函式以矩陣的方式表示，分解成三個方程式以基本簡單的電路架構，最後將三塊基本電路連結成完整橢圓濾波器電路，完成方程式轉化成濾波器電路設計。
本論文使用運算轉導放大器(OTA)與電容器(C)元件實現一個57Hz低通濾波電路，使用節點分析設計法，來設計的四階電流式橢圓低通濾波電路，電路擁有最少元件的優點。電路採用H-Spice及Matlab軟體來進行模擬。操作頻率設定在57Hz，最後利用美國半導體公司的LM13700產品，在電路板上實現低通橢圓濾波器的電路實作，希望可將電路，以電子元件組成達到商品化，並證實推導出來的橢圓濾波器電路，理論值與實際值的關聯性。希望本篇論文在日後，提供後續從事橢圓濾波器這類的研究人員，有很好的參考價值。
最後，本論文所設計的橢圓低通濾波電路，期待下線實際做成積體電路，以便在實際運用在心電圖儀器之中。

關鍵字

橢圓濾波器電路 ； 57Hz低通濾波 ； 心電圖儀

並列摘要

Abstract
The precision of a output signal, making sure the signal is in or between the programed frequency band, is very important and top priority in analog filter circuit design field. To catch the subtle signal such as human body’s physiology by cardiograph, the precision is very important but often affected by test environment and facility itself. Therefore, the precision of the filter design is a crucial topic for research.
OTA (Operational Transconductaance Amplifier) is best candidate for analog filter circuit design identified by savants recently. The main character of OTA is , where Io stands for output current, stands for positive input voltage, stands for negative input voltage, stands for trans-conductance value, and the input current I+=I-=0.The trans-conductance of OTA, it is the ration of output current ( ) and input voltage diviation , can be adjusted and controlled by bias current ( ).Some savants proposed the analytical synthesis of OTA-C circuit, which has some advantages like (1) controllable (2) a wide band of operation frequency (3) high input impedance (easy to cascade other circuit) (4) to minimize component counts (can decrease parasitical effect to minimum for raising the precision of the signal in circuit)
The realization of circuit design in thise thesis, was based on the method of analytical synthesis,node analysis and transfer function represented by matrix. And decompose transfer function into three equations for simplifying circuit building. Finally, to combine those three circuits for completing whole elliptic filter circuit.
With the advantage of node analysis to design the current-mode fourth-order elliptic low pass filter, we can have minimum component usage. Therefore, only few OTAs and capacitors can realize a 57Hz low pass filter. Before building the circuit, the simulations were based on the results of H-Spice and Matlab, and then to choose LM13700 (National Semiconductor Corp.) for OTA design selection. Finally, the connection between theoretics and experiment of proposed elliptic low pass filter were been proofed in this thesis. We hope it can be a valuable reference for those who join the research of elliptic filter afterward.
Finally, this is designed of the 57Hz low-pass elliptic filter circuit, looking off the assembly line actually made of integrated circuits for use in the actual being in the electrocardiogram apparatus.

並列關鍵字

OTA ； 57Hz Low Pass ； Elliptic Filter ； ECG ； LM13700

參考文獻

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