Parasitic Effect of the Current-Mode Second-Order OTA-C Low Pass Filter Structure

• Main Authors: W-J Chiu, 邱文榮
• Other Authors: Chun-Ming Chang
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/90126113367102609867

碩士 === 中原大學 === 電機工程研究所 === 96 === 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 Tsmc35.l process verifies the theoretical predictions.