只使用參數可調之主動元件
設計之低通、帶通及帶拒濾波電路

摘要由於運算轉導放大器(Operational Transconductance Amplifier；簡稱OTA)等效一個主動元件及一個電阻器，使得所設計的電路(i)無需使用電阻，大幅減少積體電路的製作面積，(ii)其電阻值可藉由偏壓電流的精確調整改變，使得以運算轉導放大器(OTA)及電容(Capacitor；簡稱C)設計類比電路成為一個好的研究方向。當前積體電路(IC)的製作技術無法將電容製作得很精準，使得電路的輸出訊號產生相當大的誤差，這是目前IC製作上的嚴重問題。所以尋求可調元件來取代電容以實現轉移函數中s項的作用，成為一個重要的研究方向。過去經常被使用的運算放大器(Operational Amplifier；簡稱OA)其輸出入的關係如下：；其中A0為增益大小，ω0為頻帶寬，B0為增益及頻帶寬的乘積。由上式可知，運算放大器也可以實現轉移函數中s項的作用。那麼，緊接的問題是：這個B0(增益及頻帶寬的乘積)是否也和運算轉導放大器中的轉導值(其倒數即為一等效電阻)一樣可否藉由改變偏壓電流而改變大小呢?經過本論文研究結果，吾人發現：運算放大器的B0值的確可藉由偏壓電流及其內部補償電容的調整而改變。這一個發現找到了替代電容而可以調整大小的元件了，也就是可調的運算放大器。本論文即使用可調運算放大器(Tunable OA)及可調運算轉導放大器(Tunable OTA)來設計二階濾波電路。電路的轉移函數可以選擇合適的輸入輸出端點實現低通、帶通及帶拒三種輸出信號。電路的特點是利用偏壓電流的調整來改變運算轉導放大器的轉導值和運算放大器的增益頻寬積，使得所設計的電路有很高的準確性，解決了因電容不準所產生的輸出誤差問題。最後，本論文以H-spice模擬TSMC035製程驗證模擬結果與理論相符合。

關鍵字

濾波器；帶拒；帶通；低通；主動元件；參數可調

並列摘要

Abstract It is worthy of research to do the analogue circuit design using Operational Transconductance Amplifiers (OTAs) and Capacitors (Cs) because an OTA is equivalent to both an active element and a resistor leading to a more condensed integrated circuit without resistors, and because the equivalent resistor value can be electronically tuned varying the bias current. Due to the difficulty to precisely fabricate the capacitance in integrated circuits, it becomes an important research work to find a tunable element for the replacement of the capacitor used to realize the s terms in transfer functions. The input-and-output relationship of an Operational Amplifier (OA) is shown as below. in which A0 is the gain, ω0 the bandwidth, and B0 the product of both gain and bandwidth. It is exhibited that an OA can also be used to realize the s terms in transfer functions. Hence, is the B0 variable, as the transconductance of an OTA, or not? In this thesis, we have found that the B0 is variable tuning either the bias current or the inner compensation capacitance of an OA just like the variation of the transconductance of an OTA through the tuning of its bias current. Therefore, the capacitor with error fabricated in the integrated circuits can be replaced by the OA tunable through its inner bias current. The thesis is focused on the design of biquads using both tunable OA and tunable OTA, leading to very precise output responses such as lowpass, bandpass, and band-reject filtering signals. Finally, the H-spice simulation with TSMC035 process verifies the theoretical predictions.

並列關鍵字

Band-reject ； Filter ； Low-pass ； Band-pass

參考文獻

[2] K. C. Smith and A. Sedra, “The current conveyor a new circuit building block,”IEEE Proc, vol. 56, pp. 1368-1369, 1968.

[3] B.Wilson, ”Constant bandwidth voltage amplification using current conveyor,” Int. J. Electronics, vol. 65,no. 5, pp. 983-988, 1988.

[4] Sedra/Smith,: “microelectronic circuits”, FOURTH EDITION.

[5] Masami Higashimura and Yutaka Fukui, “simulation of lossless floatinging inductance using two current conveyors and an operational transconductance amplifier,“ Int. J. Electron., vol 66 no 4, pp. 633-638, 1989.

[6] K.C. Smith and A. Sedra, “A second-generation current conveyor and it's applications, ” IEEE Trans., CT-17, pp. 132-134, 1970.

國際替代計量

只使用參數可調之主動元件設計之低通、帶通及帶拒濾波電路

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