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ISSN: 2278 – 909X International Journal of Advanced Research in Electronics and Communication Engineering (IJARECE)
Volume 4, Issue 11, November 2015
2643
All Rights Reserved © 2015 IJARECE
Simulation and Analysis of Current Differencing
Transconductance Amplifier (New Active Element)
Kailash Nath , Amit Choudhary
Abstract— In this paper a CMOS-based circuit for
realization of high-performance current mode current
differencing transconductance amplifier (CDTA) is
demonstrated. This circuit provides the advantage of a
wide frequency bandwidth and very small input terminal
impedance. Some voltage and current mode applications
using this element have already been reported in literature
.It provides linear and non-linear application. Proposed
model use the concept of bulk driven in CMOS and can be
implemented by two current conveyors and one OTA with
double current output. It has used voltage buffer
compensation technic in feedback . Design in the CMOS
technology has been verified via tanner tool simulation and
for this implantation we are applying supply voltage of
±0.6V.
Keywords –Bulk driven, CDTA, CMOS, compensation,
current conveyors (CCII±), OTA, Tanner tool
I. INTRODUCTION
Since the introduction of current differencing
transconductance amplifier (CDTA) is 2003,it has been
acknowledge to be a versatile current-mode active building
block in design circuit. This device with two current input and
two kinds of current output provides an easy implementation
of current-mode active filters [12]. It also exhibits the ability
of electronic tuning by the help of its transconductance gain
(gm) [13]. All these advantages together with its current-
mode operation nature make the CDTA a promising choice for
realizing the current-mode filters [13]. As a result a variety of
CDTA topology and application have also been considered by
various researchers.
In order to meet the demands for the electronic circuits
working on low power supply voltages and low power
consumption, signals representing the information in the form
of electric currents are used for processing [2]. Such signals
offer higher bandwidth and better signal linearity.
Kailash Nath , ECE Department, IMS Engineering College, Ghaziabad, India.
Amit Choudhary, ECE, IMS Engineering College, Ghaziabad, India.
Current conveyors and OTA is very important building
block of proposed CDTA. Current mode (Current Conveyor)
approach helps in designing circuits with lower voltage swings
and smaller voltage supply. OTA is unique device with
characteristics low power, fast settling time and higher
dynamic ranges.
Low-voltage and low-power integrated circuit design is
becoming a advancing trend in VLSI technology, especially in
special portable applications. In this proposed model, the
principle of a bulk-driven MOS transistor is employed in the
design of a Low-voltage and low-power current differencing
transconductance amplifier (CDTA)[1].
The proposed CDTA has two current conveyors (CCII±) and
one OTA. It used voltage buffer compensation technic in
feedback circuit. The CDTA element constitutes of an input
current subtraction which takes the difference of input signals
and transfers to the Z terminal [14] and a dual output
transconductance stage which is used to convert the voltage at
the z terminal to dual output currents with a transconductance
parameter +g for the positive output and –g for the negative
output voltage buffer circuit is given in fig.1. This
compensation technique provided high accuracy due to its
dependency on matching tolerances between
transconductances and capacitors. The great advantage of a
voltage buffer in the compensation branch is reduces output
swing, which use in many practical cases.
Fig.1: Voltage Buffer Compensation Circuit
This compensation technique provided good gain
bandwidth, high power supply reject ratio and improved slew
rate due to low coupling capacitance value .This circuit block
also provide area efficient due to low coupling capacitance
value . This circuit also works on power and area trade-off. It
controls output swing so that practical device is feasible. This
ISSN: 2278 – 909X International Journal of Advanced Research in Electronics and Communication Engineering (IJARECE)
Volume 4, Issue 11, November 2015
2644
All Rights Reserved © 2015 IJARECE
circuit high accuracy due to its dependency on matching
tolerances between transconductances and capacitor.
II. CURRENT DIFFERENCING TRANS-
CONDUCTANCE AMPLIFIER (CDTA)
Proposed CDTA has five nodes P, N, Z, X+ and X-. Proposed
CDTA has low impedance current input terminals (p and n)
and an auxiliary output Terminal Z.
Current is applied on input terminal P and N. The difference
of input current flows on output terminal Z [15] as shown in
Fig. 2. External impedance is connected to Z terminal and the
voltage over this terminal is converted to the output current by
the output transconductanceGm and provides positive output g
to X+ terminal and negative output –g to X- terminal.
Fig.2: Symbol of CDTA Block
Output current of X+ terminal and X- terminal is equal in
magnitude but opposite in direction. The magnitude of current
is product of transconductance g and the voltage at Z terminal
impedance and it can be shown by following equations:
Vp = Vn = 0 (1)
Iz = Ip – In (2)
Ix = g.Vz = g.Zz.Iz (3)
Ix+ = g.Vz (4)
Ix = - g.Vz (5)
These equations show the all possible implementation of
CDTA. Here the voltage of the terminal P, N, Z and X are
shown as Vp ,Vn , Vz and Vx. For CDTA, the following
equations are true:
(6)
Current Differencing Transconductance Amplifier is a new
active element with two current inputs and two current
outputs. This element has two stages BD-CDU (Current
Differencing Unit) and OTA (Operational Transconductance
Amplifier). BD-CDU is formed with two OTAs namely OTA
1 and OTA 2. Each OTA works as a separate current conveyor
of opposite types. Input to OTA 1 is Ip and input to OTA 2 is
In. The input to the first stage i.e. BD- CDU are two currents
Ip and In and output is the difference current Iz. And voltages
at terminals P and N are taken to be zero (0) as terminals P
and N are internally grounded which is given in above matric
and below in fig.3.
Fig.3: CDTA Implementation by Bulk-Driven OTAs
ISSN: 2278 – 909X International Journal of Advanced Research in Electronics and Communication Engineering (IJARECE)
Volume 4, Issue 11, November 2015
2645
All Rights Reserved © 2015 IJARECE
III. PROPOSED CIRCUIT IN CMOS
IMPLEMENTATION
Fig.4: Internal Circuit of BD-CCII- Block
Fig.5: Internal Circuit of BD-CCII+ Block
Fig.6: Internal Circuit of OTA Block
Fig.7: Voltage Buffer Compensation CMOS Circuit
ISSN: 2278 – 909X International Journal of Advanced Research in Electronics and Communication Engineering (IJARECE)
Volume 4, Issue 11, November 2015
2646
All Rights Reserved © 2015 IJARECE
IV. SIMULATION RESULT
Fig.8: DC Response Iz vs Ip
Fig.9 Frequency Response Iz/Ip in Magnitude, where Vz=0
Fig.10: Frequency Response Iz/Ip in Current Phase, WhereVz=0
V. CONCLUSION
This paper represents a Current Differencing
Transconductance Amplifier (new active element) employing
bulk driven technique and Voltage buffer compensation
technique. The compensation technique provided a high gain-
bandwidth product and highly reduces output swing. The main
advantage of the designed CDTA is that it works on low
supply voltage and low power consumption. The -3dB
bandwidth of Iz/Ip and Iz/In are 36.75MHz. The proposed
CDTA can be useful in application where low supply voltage
is required. The new CDTA have high linearity, wideband,
bulk-driven OTA with tunable transconductance. The Design
is operating at a voltage of ±0.6 V.
ISSN: 2278 – 909X International Journal of Advanced Research in Electronics and Communication Engineering (IJARECE)
Volume 4, Issue 11, November 2015
2647
All Rights Reserved © 2015 IJARECE
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Author’s Profile:
Kailash Nath has received his B.Tech degree in
Electronics and Communication Engineering from Gautam Buddh Technical
University, India in 2013. This author is pursuing M.Tech in VLSI Design
from I.M.S. Engineering College, Ghaziabad, from UPTU, Uttar Pradesh,
India. His major areas of research work include Analog Circuit Design.
AmitChoudhary is Asst. Prof. at I.M.S. Engineering
College, Ghaziabad, Uttar Pradesh. He has received his M.Tech degree in
VLSI Design from UPTU, Currently he is purusing Ph.D from JMI Delhi,
India. His major areas of research work include Analog Filter Circuit Design
and intelligent wireless sensor.