Tunable Current Conveyor And Its Current-mode Filters

With high speed low power and simple structures, current-mode circuit becomes a research focus in the microelectronic circuit and system. As a standard block of current-mode circuits, current conveyor and its filters have received considerable attentions for its innovative design, low power dissipation and high gain bandwidth, moreover, the circuit are continually studied to improve its performance.This paper mainly focuses on the principles and the design methods of electronic controllable current conveyor and its filters. The paper is organized as follows:First, the development and characteristics of the current-mode circuit are introduced and a simple contrast with the traditional voltage mode circuit is made; then the basic theory of the current-mode circuit including the performance of current mirror, the development and theory of current conveyor and design theory of current-mode filter are introduced.Based on the research in current mode circuit and current conveyor, this thesis proposes a high performance CMOS Electronically Tunable current conveyor (ECCII) circuit; then a ECCII based filter is designed, and a high order elliptic filter is designed based on the current control fully balanced current conveyor II (CFBCCII). the filters are simulated by PSPICE. In the end, This paper compares the ECCII based filter with the CFBCCII based filter. The main tasks of this paper are listed as follows:(1) The performance of ECCII is analyzed. The circuit designed in this paper has a good voltage and current tracking accuracy. A low impedance in the input terminal X and a high impedance in the output terminal enable easy cascade connection.(2) An ECCII based universal filter is proposed. The quality factor and natural frequency of this filter can be controlled electronically by adjusting the ratio of dc bias currents of the ECCII; the low-pass response is obtained with a high impedance and has a variable gain which can be changed by the biasing current of ECCII. Simulation results confirm the expected good performance of the proposed ECCII in terms of output resistance, linearity, frequency response, tunability, and power consumption.(3) A differential current-mode high-order elliptic filter based on CFBCCII is proposed. The circuit adopts fully balanced structure, the input and output terminals are differential which can restrain disturbing of even-order harmonic and common mode signals in a great extent. The cut-off frequency of this filter can be controlled by dc biasing current, meanwhile, the low sensitivity characteristics of passive electrical network is also reserved. All the RC passive components are grounded, which makes its integration much easier. Finally, the PSPICE simulation shows the tunable characteristic of cut-off frequency.