Current-Mode Second-Order OTA-C High Pass Filter Structure with High-Frequency Investigation
| Autor: | Ping-Cheng Lin, 林炳成 |
|---|---|
| Rok vydání: | 2008 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 96 In the last few years, the current-mode circuit is proved to be much more precise than its voltage-mode counter part. Since the transconductance of an Operational Transconductance Amplifier (OTA) and the inner intrinsic resistance at terminal x of a second-generation current controlled conveyor (CCCII) are electronically adjusted by the internal bias current,no resistors in the OTA-C or CCCII circuit become an important advantage in the active filter design. The thesis studies why is the circuit by the OTA,because CCCII has other shortcomings:1. Voltage tracking error。2. Current tracking error。 It is worthy of research to do the analogue circuit using Operational Transconductance Ampplifiers (OTA) and Capacitors (C), 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。 There are several kinds of parasitic capacitances, including input and output parasitic capacitances of an OTA and the nodal parasitic capacitance at the internal node in an OTA-C (Operational Transconductance Amplifier and Capacitor) circuit. This leads to the difficulty to have the same places for both given capacitors and all the parasitic capacitances. When the differential-input OTA and floating capacitances are employed in the circuit structure, and the impossibility to obtain a high–frequency circuit with precise output responses by giving a proper capacitor value after absorbing the parasitic capacitance。 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 non-ideal effect in an OTA is resulted from the parasitic capacitances spreaded among the MOS transistors which are called the frequency dependent transconduce, namely, the ratio between the output current phasor and the input voltage phasor, of an OTA. The non-ideal effect out of the OTA includes the input and output parasitic capacitance and the output parasitic conductance of an OTA and the nodal parasitic capacitance at each internal node。 In this thesis, a current-mode second-order OTA-C universal filter structure is used for example to demonstrate this new improvement for a high-frequency circuit. When the simulation resonance frequency is lower than the theoretical value,this implies that the given transconductance is also higher than the exact value. The reduction of the given transconductance leads to approach the theoretical prediction. On the contrary, if the simulation resonance frequency is lower than the theoretical value, it means that the additional parasitic capacitance makes a total capacitance larger than the exact value. Finally, The above proposed improvement was verified by UMC035 H-spice simulation。 |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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