International Journal of Research in Electronics & Communication Technology
Volume 1, Issue 2, October-December, 2013, pp. 76-80, © IASTER 2013
www.iaster.com, ISSN Online: 2347-6109, Print: 2348-0017
Implementation of Precision Full-Wave Rectifier
using CNTFET
Aatreya Vivek M*, P. Reena Monica**
*
M. Tech VLSI Design, **Assistant Professor (Sr.)
SENSE, VIT University Chennai Campus, Chennai, Tamil Nadu, India
ABSTRACT
We are hitting a road block scaling down the conventional MOSFET devices because of the
exponential increase in the sensitivity of the device parameters and the sophistication of the
fabrication techniques. CNTFET is a promising alternative with low power consumption and better
performance which will help us to prolong Moore’s law. In this paper, using CNTFET, a Precision
Full-Wave Rectifier is implemented with the help of a DDCC (Differential Difference Current
Conveyor) in Cadence Virtuoso tool. The implemented design has low design complexity, larger
bandwidth of operation and higher packing density.
Keywords: Amplifier, Cadence, CNTFET, DDCC, Rectifier.
1. INTRODUCTION
Full-wave rectifier is used in RF demodulator, piecewise linear function generator, AC voltmeter,
wattmeter, and various nonlinear analog signal processing circuits [1]. A typical rectifier realized by
using diodes, cannot rectify signals whose amplitudes are less than the threshold voltage
(approximately 0.7V for silicon diode and approximately 0.3 for germanium diode) [2]. Hence the
diode based rectifiers are used in applications where the accuracy in the range of threshold voltage is
not important. Moreover, the rectifiers based of operational amplifiers and resistors cannot be used as
they are not suitable for IC fabrication because of their size. To overcome these obstacles, a precision
full-wave rectifier using a DDCC (Differential Difference Current Conveyor) could be used. In the
previous works on DDCC [3] with CMOS (350nm), the circuits suffer from the problem of leakage
current. Hence to avoid this problem, CNTFETs can be used in the place of CMOS. Hence the DDCC
implementation with CNTFETs shows better performance with higher packing density.
2. CARBON NANOTUBE
A monolayer of graphite is called graphene, and a carbon nanotube (CNT) is a cylinder made of
graphene. CNTs are broadly classified into two types namely single-walled carbon nanotubes
(SWCNTs) and multi-walled nanotubes (MWCNTs) as shown in the figure 1. The way the graphene
sheet is wrapped is represented by a pair of indices (n,m) called the chiral vector. The integers n and m
denote the number of unit vectors along two directions in the honeycomb crystal lattice of graphene.
SWCNT can further be classified into Arm-Chair, Zigzag and Chiral which can be described by the
chiral vector (n, m), where n and m are the integers of the vector equation R = na1 + ma2.
76
International Journal of Research in Electronics & Communication
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Graphene
SWCNT
ISSN
(O) 2347-6109
(P) 2348-0017
MWCNT
Fig 1. Three Types of Carbon Nano Tube
The values of n and m determine the way the nanotube is folded into a cylinder. If m = 0, the
nanotubes are called zigzag nanotubes, and if n = m, the nanotubes are called armchair nanotubes.
Otherwise, they are called chiral. Moreover the chirality determines the diameter of the nanotube too
and the differences in the chiral angle and the diameter cause the differences in the properties of the
various carbon nanotubes.
3. CARBON NANOTUBE FIELD EFFECT TRANSISTOR
A carbon nanotube field-effect transistor (CNTFET) refers to a field-effect transistor that utilizes a
single carbon nanotube or an array of carbon nanotubes as the channel material instead of bulk silicon
in the traditional MOSFET structure. The electronic transport in CNTs occurs ballistically (without
scattering) over long lengths owing to their nearly one dimensional electronic structure. This enables
nanotubes to carry high currents with negligible heating. Moreover, because of the lack of boundaries
in the perfect and hollow cylinder structure of CNTs, there is no boundary scattering too.
A carbon nanotube’s band-gap and the threshold voltage of the CNTFET are dependent on its chirality
and diameter of the nanotube. The threshold voltage and the band gap energy are directly proportional
to each other and both of them in turn are inversely proportional to the diameter of the carbon
nanotube. The threshold voltage, band gap energy and the diameter of CNT are related as shown in the
equation (1) [4]
(1)
where ɑ = 2.49Å is the carbon to carbon atom distance, Vπ=3.033eV is the carbon π- π bond energy
in the tight bonding model, e is the unit electron charge, and DCNT is the diameter of the CNT which
is calculated by the equation (2)
(2)
where ɑ 0 = 0.142 is the interatomic distance between each carbon atom and its neighbor.
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International Journal of Research in Electronics & Communication
Technology, Volume-1, Issue-2, October-December, 2013, www.iaster.com
ISSN
(O) 2347-6109
(P) 2348-0017
In this paper, we are using a Verilog-A formulation of the Stanford compact model of CNTFET [5] [6]
in Cadence EDA tool to implement a precision full-wave rectifier in 32nm technology.
4. THE DDCC DEVICE
A differential difference current conveyor combines features of a differential difference amplifier and
a current conveyor. A differential difference amplifier is a fundamental amplifier circuit which is
widely used in opamp circuits because of its simplified design process. But like the conventional
opamp circuit, performance of the differential difference amplifier is limited by its finite gainbandwidth product, so it is unsuitable for application in high frequency circuits. A device called a
current conveyor is a current mode amplifier which is quite appropriate for high frequency circuits.
DDCC (differential difference current conveyor) is a device that combines the characteristics of both a
differential difference amplifier and a current conveyor and hence has a superior finite gain-bandwidth
product. Therefore it is suitable for high frequency applications.
The electrical symbol of DDCC [7] and its input-output characteristics are shown in the figure 2. It has
three voltage input terminals: Y1, Y2 and Y3, which have high input impedance. There is a low
impedance current input terminal X and a high impedance current output terminal Z.
Fig. 2. DDCC Circuit Symbol and its Input-Output Characteristics
The circuit diagram for the DDCC device [2] using the Stanford compact model of CNTFET is
implemented and is shown in the figure 3.
Fig. 3. Circuit Diagram of DDCC
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International Journal of Research in Electronics & Communication
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ISSN
(O) 2347-6109
(P) 2348-0017
The characteristics obtained for the DDCC device is shown in the figure 4 where Vx is plotted against
Vy1 for different values of Vy2.
Fig. 4. Input-Output Characteristics of DDCC
5. IMPLEMENTATION OF PRECISION FULL-WAVE RECTIFIER
Basically a full wave rectifier converts an AC
signal into a pulsating DC signal. Using the
previously implemented circuit of DDCC as a
basic building block, the full wave rectifier
circuit [9] is constructed as shown in the
figure 5.
Fig. 5. Full-wave Rectifier Circuit
In the full wave rectifier circuit shown in the
figure 5, when the input signal Vin > 0, Vin is reflected at the output Vout by DDCC1 while the
DDCC2 is turned off. And when Vin < 0, Vin is reflected at the output Vout by DDCC2 while the
DDCC1 is turned off. Therefore the given circuit provides full-wave rectification.
The characteristics obtained from the simulation of the given full-wave rectifier circuit is shown in the
figure 6.
Fig. 6. Response of Precision Full-wave Rectifier made using CNTFET
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International Journal of Research in Electronics & Communication
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ISSN
(O) 2347-6109
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The characteristics shown in the figure 6 is a response of a full-wave rectifier implemented using a
CNTFET. The same procedure was repeated
and the full-wave rectifier circuit was
implemented using CMOS devices. The
response obtained from a CMOS circuit is
shown in the figure 6.
From the obtained simulation results, we can
observed that the rectifier implemented using
CNTFETs can rectify any signal with
amplitudes as low as 20mV whereas
conventional rectifiers constructed using
CMOS require minimum applied voltage to
be above the knee voltage of the
semiconductor material used.
Fig. 6. Response of Precision Full-wave rectifier made using CMOS FET
6. CONCLUSION
Carbon Nanotube Field Effect Transistor provides a vast field of research in the area of nanoelectronics and a number of different circuits can be implemented using CNTFETs. In this work, a
precision full-wave rectifier circuit is implemented in Cadence using the Verilog-A model of CNTFET
and the results show that they have better performance and higher device density when compared to
the conventional CMOS counterparts.
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