ISSN: 2278 909X International Journal of Advanced Research ...ijarece.org/wp-content/uploads/2015/11/IJARECE-VOL-4-ISSUE-11-2643-2647.pdf · March 2015. Author’s Profile: Kailash

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



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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



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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



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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.



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March 2015.

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.

Documents

ISSN: 2278 909X International Journal of Advanced Research ...ijarece.org/wp-content/uploads/2015/11/IJARECE-VOL-4-ISSUE-11-2643-2647.pdf · March 2015. Author’s Profile: Kailash