高差動輸入訊號及共模電壓範圍之五階轉導電容濾波電路

Abstract

本篇論文設計了一具有高差動輸入訊號及高共模輸入電壓範圍的五階低通gm-C濾波器。在設計出此一濾波器之前，我們必須先設計出一具有低電壓高差動輸入訊號及高共模輸入電壓範圍的轉導放大器（電壓－電流轉換器）。此轉導放大器是由一Ｎ型的轉導放大器電路並聯一Ｐ型的轉導放大器組合而成。並且此兩個轉導放大器在輸出端分別連接一電流鏡，以求達到一個具有高差動輸入訊號及高共模輸入電壓範圍的電路。對gm-C濾波器而言，其有一使用調整電路來補償製程與溫度變化的必要性。而在本篇論文中我們必須使用到兩個調整電路來分別對Ｎ型轉導放大器以及Ｐ型轉導放大器來做電路的控制電壓調整動作，以求此濾波器能有一固定及穩定的截止頻率，並且維持Ｎ型轉導放大器與Ｐ型轉導放大器之間轉導值的相等。此濾波器是操作在1.8V的供應電壓下，截止頻率可調範圍為1.6MHz至2.4MHz之間，功率消耗為0.75mW，並且具有±0.7V的高差動輸入訊號及高共模輸入電壓範圍。

This thesis presents a low-voltage CMOS fifth-order elliptic low-pass gm-C filter with large differential input swings and wide common-mode ranges. The Operational Transconductance Amplifier (OTA) is a low-voltage CMOS voltage-to-current (V-I) converter. The basic OTA cell with NMOS-inputs is connected in parallel with its counterpart PMOS-input OTA circuit, in conjunction with NMOS and PMOS output current mirrors, to achieve large input signal and common-mode voltage ranges. For the gm-C filter, additional tuning circuitry is required in order to compensate the process and temperature variation.. In this OTA design, two frequency tuning circuits are utilized, respectively, to adjust the control voltage of NMOS-input and PMOS-input OTAs so as to fix the filter cutoff frequency and also maintain the equivalence between the two transconductance of NMOS-input and PMOS-input OTAs. The gm-C filter operates with supply voltage of 1.8V, has cutoff frequency of 1.6MHz to 2.4MHz, dissipates 0.75mW power, and has large differential input signals and wide common-mode voltage ranges of ±0.7V.