具有最少元件的電流式OTA-C三階橢圓濾波電路於高頻操作時非理想效應之研究與改進

Non-ideal Effect and Improvement of the Current-Mode Third-Order High-Frequency OTA-C Elliptic Filter Structure with the Minimum Components

王俊傑(Jyun-Jie Wang)

指導教授 ： 張俊明

中原大學/工學院/電機工程研究所/碩士(2007年)

https://doi.org/10.6840/cycu200700365

摘要

利用運算轉導放大器(OTA)與電容器(C)做類比電路設計是一個值得研究的方向，其主要原因為運算轉導放大器(OTA)不僅具備主動元件特性並且可藉由等效電路代替電阻器，使得在積體電路中無需使用電阻器，而且可由偏壓電流的調整改變其等效電阻值。

近年來，由於分析合成法(Analytical Synthesis Method)的提出，使得以OTA-C 為主要架構之濾波電路同時具備了以下三項優點：
(1)使用單端輸入的OTA(可免除寄生電容的Feed-through 效應)，(2)使用接地電容(可直接吸收寄生電容)，(3)使用最少的主動元件，且所有外加電容位置恰好與所有寄生電容的位置相同，吸收了寄生電容，並減少寄生效應對整體電路的影響。

在OTA-C 的電路中，由於寄生電容效應種類繁多與內部的非理想效應，造成輸出信號高頻部分產生失真，吾人利用所求得OTA 與頻率變化有關的轉導函數並針對其非理想效應做深入研究，主要目的希望提升OTA-C 濾波電路操作頻率範圍，實驗結果也證實非理想效應的確對輸出信號產生影響。

在了解非理想效應對輸出信號之影響後，為有效改善非理想轉導值對電路產生的影響，吾人提出利用可調運算轉導放大器(Tunable OTA)並利用調整的方式改善OTA 之非理想效應，解決因為非理想效應與寄生效應所產生的問題，使電路準確性提高，最後，本論文以H-spice 軟體進行電路模擬，所使用製程參數為TSMC035μm，並於實際模擬結果與理論之間相互得到驗證。

關鍵字

運算轉導放大器 ； 電流式 ； 橢圓濾波電路

並列摘要

It is worthy of research to do the analogue circuit using Operational Transconductance Ampplifiers (OTAs) and Capacitors (Cs), because an OTA with the property of an active element can replace a resistor such that no resistors will be needed in the integrated circuit. In addition, the equivalent resistor value can be electronically tuned by varying the bias current.

Recently, owing to the appearance of “Analytical Synthesis Method”,the circuit with third-order OTA-C elliptic filters has achieved the three following important advantages: (i) using single-ended-input OTAs(overcoming the feed-through effect due to the use of differential-input OTAs), (ii) using grouded capacitors (absorbing the shunt parasitic capacitance),and (iii) using the minimum components and all the parasitic capacitances have the same places as those of all the given capacitors in the realized circuits.

The output signals will be distorted in the high frequency as a result of the varieties of parasitic capacitances and the non-ideal effect. Therefore,taking the non-ideal effect of OTAs into consideration, we analyze the ratio of the output current to the input voltage of OTAs, which is called frequency dependent transconduce
,for the purpose of increasing the switching frequency in the filter structure. The experimental results also show that the non-ideal effect indeed influences the output signal.

Based on the non-ideal effect upon the output signal and the improvement on the frequency dependent transconduce, we propose a method that adopts tunable OTA to improve the non-ideal effect of OTA to solve the problems resulted from the non-ideal effect and parasitic effect. Accordingly, the signal can be output more precisely. Finally, the H-spice simulation with TSMC035 process verifies the theoretical predictions.

並列關鍵字

filter ； OTA ； minimun components ； elliptic

參考文獻

[1] C. M. Chang; Al-Hashimi, B. M. “Analytical Synthesis of Current

[2] C. M. Chang; Al-Hashimi, B.M. “Analytical Synthesis of voltage

mode OTA-C all-pass filters for high frequency operation”, ISCAS

[3] C. M. Chang; Al-Hashimi, B.M. “New high-order filter structures

using only single-ended-input OTAs and grounded capacitors”, IEEE