Circuits and Systems, 2011, 2, 14-17

doi:10.4236/cs.2011.21003 Published Online January 2011 (http://www.SciRP.org/journal/cs)

Copyright © 2011 SciRes. CS

A Novel Multifunction CFOA-Based Inverse Filter

Hung-Yu Wang1, Sheng-Hsiung Chang2, Tzu-Yi Yang1, Po-Yang Tsai1

1Department of Electronic Engineering, National Kaohsiung University of

Applied Scienc es, Ka o hsiu n g, Taiwan, China

2Department of Optoelectronic Engineering, Far East University, Hsin-Shih, Taiwan, China

E-mail: hywang@cc.kuas.edu.tw

Received October 7, 2010; revised November 3, 2010; accepted November 17, 2010

Abstract

We present a novel multifunction inverse biquad configuration based on current feedback operational ampli-

fiers (CFOAs) and grounded passive elements. The proposed scheme can be used to realize inverse lowpass,

inverse bandpass and inverse highpass filter functions. The relevant coefficients of the inverse filters are or-

thogonal adjustable by independent passive elements. All the passive elements in the proposed scheme are

grounded to benefit easier electronic tunability. With the high input impedance and low output impedance

properties, the scheme is input and output cascadable for voltage operation. The feasibility of the proposed

scheme is demonstrated by HSPICE simulations.

Keywords: Multifunction, Inverse Filter, CFOA

1. Introduction

In communication, control and instrumentation systems,

there are numerous situations in which an electrical sig-

nal is altered through a linear or nonlinear transformation

by a processing or a transmission system. So it is neces-

sary to recover the input signal from the available dis-

torted output signal resulted from the signal progress.

This can often be done by using a system that has an

inverse transfer characteristic of the original system [1].

For digital signal processing, several methods for ob-

taining digital inverse filters have been established [2].

Nevertheless, for analog signal processing, only a few

works are known for realizing continuous-time analog

inverse filters [1,3-6].

In [1], a general approach is presented for obtaining

the inverse transfer function for linear dynamic systems

and the inverse transfer characteristic for non-linear re-

sistive circuits. In [3], a procedure for deriving cur-

rent-mode, four-terminal floating nullor (FTFN)-based

inverse filter from the voltage-mode filter is given. It

uses the method in [1] and dual transformation [7] during

the procedure. Due to the use of dual transformation, this

approach can only be applied to planar circuit. By the use

of adjoint transformation, another easier procedure for

deriving current-mode FTFN-based inverse filter from

the voltage-mode filter is presented and it is applicable to

nonplanar circuits [4]. All the proposed approaches in

[1,3,4] are useful for obtaining single-input single-output

inverse filters. Additional various inverse current-mode

and voltage-mode filters are presented in [5] and [6],

respectively. However, each circuit proposed in [5,6] has

one inverse filter function. In this paper, we present a

novel inverse filter scheme based on CFOAs and

grounded passive elements. By slight modification of the

passive elements of the proposed scheme, various in-

verse filter functions can be realized. The presented

scheme possesses high input impedance and low output

impedance which enables the convenience of connecting

with the other stage in cascade. The workability of the

proposed scheme is verified by HSPICE simulations.

The simulated results confirm the theoretical prediction.

2. The Proposed Circuit

The current-feedback operational amplifier, such as

AD844 from Analog Devices Inc. [8], has gained the

acceptance of researchers as a building block in circuit

design. The advantages of CFOAs are their constant

bandwidths, independent closed-loop gains and high

slew-rate capabilities [9]. The CFOA can be described

using the following matrix-relations:

0100

0000

1000

0010

xx

yy

zz

ww

VI

V

V

VI

. (1)