高速高線性度之轉導式運算放大器

Abstract

在類比濾波器電路中，相較於主種動式RC濾波器、切換式電容濾波器等其他種類的類比率波器，轉導電容式濾波器更適合被運用在高頻率上。而轉導式運算放大器則是轉導電容式濾波器中最重要的基本元件。對轉導放大器而言，線性度較差是主要的缺點，所以如何改善線性度變成一個很重要的課題。而本論文提出的兩種改善轉導式運算放大器線性度的架構，可以用來製作高線性度的轉導電容式濾波器轉導。在本論文中，除了提高電路的線性度，並且能夠操作在高速度，與其他研究文獻相比，也擁有較低的功率消耗。 本論文實現兩種不同提升線性度的架構與技術。第一種電路架構，讓輸入對N型電晶體操作在飽和區，並利用調節疊接組態來固定它們的汲極至源極端跨電壓，有效提高電路的線性度。除了提高線性度，電路還具有調整轉導值的功能，可以補償轉導值因製程誤差所造成的偏移。此轉導放大器以台積電0.18μm CMOS 1P6M 製程實現，使用面積為 。它的工作電壓為1.2V且功率消耗為0.335mW。而第三項諧波失真在輸入訊號頻率40MHz且振幅為0.3Vpp時的大小是-65.9 dB，並且在同樣條件下的三階交互調變為-57 dB。 第二種電路使用改良的三極區補償飽和區遷移率減少的補償電路架。比起傳統的遷移率減少補償電度，此種改良架構能更能利用在高頻率，且有效消除第三項諧波失真，所以擁有良好的線性度。除此之外，電路一樣也具有調整轉導值的功能。此轉導放大器以台積電0.18μm CMOS 1P6M 製程實現，使用面積為 。它的工作電壓為1.8V且功率消耗為1.3mW。而第三項諧波失真在輸入訊號頻率30MHz且振幅為0.4Vpp時的大小是-70.6dB，並且在同樣條件下的三階交互調變為-62 dB。

Compared with the other types of analog filters, such as active-RC or switched-capacitor filters, transconductance-C filters are usually used for high-frequency analog filters. The Operational transconductance amplifier (OTA) is the most important building block in the transconductance-C filters. Poor linearity is the drawback of the OTA. Therefore, it is an important project to improve the linearity of the OTA. In this thesis, two linearity enhancement techniques for OTA to build the transconductance-C filter are proposed. The proposed circuit can be operated at high speed with improved linearity. Compared with other papers, these circuits have lower power consumption as well. In this thesis, two linearity-improved structures and techniques have been implemented. The first one improves linearity effectively by using MOFETs operating in the saturation region with constant Vds by regulated cascode stage. In addition to improving linearity, the circuit has the function of tuning transconductance, which can compensate for the offset of transconductance caused by the process variation. The OTA fabricated by TSMC 0.18um CMOS 1P6M technology occupies the area of . It works under a 1.2V supply voltage with 0.335mW power consumption. The measurement results show the HD3 of -65.9dB and the IM3 of -57dB with 0.3-Vpp 40MHz input signal. The second one uses the mobility compensation technique for MOFETs in the triode region to compensate MOFETs in the saturation region. Compared with the conventional mobility compensation circuits, this proposed structure can reduce HD3 effectively. Therefore, this circuits have great linearity with the function of tuning transconductance. The OTA fabricated by TSMC 0.18um CMOS 1P6M technology occupies the area of . It works under a 1.8V supply voltage with 1.3mW power consumption. The measurement results show the HD3 of -70.6dB and the IM3 of -62dB with 0.4-Vpp 30MHz input signal.