Right from the beginning of electronics, there was need
of invention of new miniaturized active devices. This important aspect was
driven to the birth of transistors which had been used in amplifiers, impedance
converters, filters, etc… Later on the
voltage operational amplifier had rapidly become the main analog building block
and had dominated the field of analog electronics which happens to the first
analog integrated circuit. The voltage operational amplifier has some
limitations, such as constant gain- bandwidth product and trade-off between
speed and bandwidth. Nowadays, this situation has changed because there is a
new invents called current mode circuits, which are able to overcome the
limitation of voltage mode circuits. The performance of current mode circuits
is better in terms of low-voltage characteristics, better slew-rate and higher bandwidth.
Another important aspect, in the field of electronics on
which the researchers are always focuses on the development of low voltage /
low power devices and portable systems which operates on low supply voltage driven
by a single battery cell.
Here motive is to finding alternative which is preferably
simpler in circuit realizations that uses current signals rather than voltage
signals for signal processing. The bipolar junction transistors basically
processes voltage signals rather current signals whereas MOS-transistors are more suitable for
processing currents rather than a voltage because the output signal is current
both in common-source and common-gate amplifier configurations and common-drain
amplifier configuration is almost useless at low supply voltages because of the
bulk-effect present in typical CMOS-processes.
Moreover, MOS current-mirrors are more accurate and less
sensitive to process variation than bipolar current-mirrors because with the
latter the base currents limit the accuracy. Therefore, at the very least,
MOS-transistor circuits should be simplified by using current signals in
preference to voltage signals. For this reason, integrated current- mode system
realizations are closer to the transistor level than the conventional voltage-
mode realizations and therefore simpler circuits and systems should result.
When signals are widely distributed as voltages, the parasitic capacitances are
charged and discharged with the full voltage swing, which limits the speed and
increases the power consumption of voltage-mode circuits.
Current-mode circuits cannot avoid nodes
with high voltage swing either but these are usually local nodes with less
parasitic capacitances. Therefore, it is possible to reach higher speed and
lower dynamic power consumption with current-mode circuit techniques.
Current-mode interconnection circuits in particular show promising performance.
signal processing applications require the use of different kinds of active
devices. These active devices are classified as current-mode and voltage-mode
circuits. The majority of the active devices, already known or new ones, can be
designed by using four unity-gain cells (UGCs), namely: voltage follower,
voltage mirror, current follower, and current mirror 1, 2. Furthermore, the
combination or superimposing of UGCs leads to the generation of mixed-mode
circuits such as current conveyors (CCs) 3, and current-feedback operational
amplifiers (CFOAs) 2. Some applications of CCs and CFOAs include sinusoidal
and chaotic oscillators 4, 5.
From a circuit point of view, there are three
basic classes of nonlinear network elements, namely, resistors, inductors, and
capacitors. By definition, a two-terminal device is said to be a nonlinear
resistor, inductor, or capacitor if it is characterized by an i-v, ?-i, or q-v
curve, respectively. When the i-v, ?-i, or q-v relationship consists of a
straight line through the origin, the device is said to be linear, and the
slope of the straight line is equal numerically to the conductance, inductance,
or capacitance of the respective element. When the i-v, ?-i, or q-v
relationship doesn’t consist of a straight line, the element is said to be
nonlinear. There are two types of nonlinearity called concave and convex
nonlinearity. Chua 6,7 introduced four new network elements, namely, the
rotator, mutator, the scalar, and the reflector. The current conveyor 8 will
be used to obtain implementations that are in closer match to the ideal
equations defining the elements.