 Open Access
 Total Downloads : 688
 Authors : Mrugesh K. Gajjar, Nilesh D. Patel
 Paper ID : IJERTV3IS20947
 Volume & Issue : Volume 03, Issue 02 (February 2014)
 Published (First Online): 27022014
 ISSN (Online) : 22780181
 Publisher Name : IJERT
 License: This work is licensed under a Creative Commons Attribution 4.0 International License
Analysis of CMOS Second Generation Current Conveyors
Mrugesh K. Gajjar,
PG Student,
Gujarat Technology University, Electronics and communication department, LCIT, Bhandu Mehsana, Gujarat, India
Nilesh D. Patel, Research Scholar,
Institute of technology, Nirma University, Electronics and communication department
Ahmedabad, Gujarat, India
Abstract This paper describes the current conveyors used as a basic building block in a variety of electronic circuit in instrumentation and communication systems. Today these systems are replacing the conventional Opamp in so many applications such as active filters, analog signal processing. Current conveyors are unity gain active building block having high linearity, wide dynamic range and provide higher gain bandwidth product. The authors have simulated above configuration using TSMC 0.18m CMOS technology and the results are also tabulated for comparison.
Keywords Current conveyor, Current mode, Current mirror, CCII, CFOA.

INTRODUCTION
In analog circuit design, there is often a large request for Amplifiers with specific current performance for signal processing. The currentmode approach [5,7] considers the information flowing on timevarying currents. Currentmode techniques are characterized by signals as typically processed in the current domain. The currentmode approach is also powerful if we consider that all the analog IC functions, which traditionally were been designed in the voltagemode, can be also implemented in currentmode. In voltage mode circuits, the main building block used to add subtract, amplify, attenuate, and filter voltage signals is the operational amplifier.
A wellknown currentmode circuit is the CurrentFeedback Operational Amplifier (CFOA) [8,9,10]. This circuit, if compared to the traditional voltage OA, shows a constant bandwidth with respect to the closedloop gain and a very high slewrate. This makes this circuit of primary importance in the design of modern LV LP ICs The first stage of CFOA is the current conveyor (CCII) and the second stage is a voltage follower which can be implemented using CCII since, CCII Architecture consist of voltage follower followed by Current follower.
Current conveyors and related currentmode circuits have begun to emerge as an important class of circuits with properties that enable them to rival their voltagemode counterparts in a wide range of applications. As a matter of facts, CCII can be considered the basic currentmode building block because all the active devices can be made of a suitable connection of one or two CCIIs. It will be particularly
attractive in the environment of portable systems where a low supply voltage, given by a single cell battery, is used. These LV circuits have to show also a reduced power consumption to maintain a longer battery lifetime. This implies a reductions of the biasing currents in the amplifier stages, with consequent reduction in some amplifier performance. The currentmode approach suffers less from this limitation, while showing full dynamic characteristics also at reduced supply levels and good highfrequency performance.

CURRENT CONVEYOR
Current conveyors are unity gain active elements exhibiting high linearity, wide dynamic range and high frequency performance than their voltage mode counterparts. A current mode approach is not just restricted to current processing, but also offers certain important advantages when interfaced to voltagemode circuits. Since their introduction in 1968 by Smith and Sedra [4] and subsequent reformulation in 1970 by Sedra and Smith [5], current conveyors lot of research has been carried out to prove usefulness of this CCII. The CCII is a functionally flexible and versatile, rapidly gaining acceptance as both a theoretical and practical building block. CCII is a three terminal device, schematically represented as:
Figure 1: Second generation current conveyors.
The currentmode approach suffers less from this limitation, while showing full dynamic characteristics also at reduced supply levels and good highfrequency performance.
The electrical characteristics of CCII can be shown using matrix:
good biasing sources showing high resistances as:
( 01 + 1 )
= 1 + 1 01 1
(3)
1 +
( 02 + 2 )
2 02
2
Figure 2: Characteristics of CCII.
The X node impedance can be obtained by neglecting some
The output current IZ thus depends only on the input current at terminal X, in Fig. 1. This current may be injected directly at
components as:
=
1
03 + 04
1
+
(4)
X, or it may be produced by the copy of the input voltage VY,
3 + 4 +
3
4
from terminal Y, acting across the impedance connected at X. In a class II current conveyor input Y draws no current, whereas, for the older class I formulation, the impedance connected at X is also reflected at Y. The + sign indicates
03 04
The impedance seen at Z node is typically high and it is given by:
whether the conveyor is formulated as an inverting or non inverting circuit, termed CCII or CCII+. By convention, positive is taken to mean IX and IZ both flowing
= 07 08
07 + 08
(5)
simultaneously towards or away from the conveyor [6].

CHARACTERIZATION OF CURRENT CONVEYORS

Class AB Second generation Current Conveyor based on Current Mirror.

Class AB Second generation Current Conveyor based on a Differential Pair.
Figure 4: Class AB CCII based on Differential Pair.
In this circuit, if the MOS output resistance is negligible, the voltage transfer error is always close to unity [1].
05 06
(5 + 6) 0 2
Figure 3: Class AB CCII based on Current Mirror.
= = 05 + 06 2
2
(6)
05 06 5 + 6 0 1 + 1
1
In this circuit, IBias1 and IBias2 have to be equal [7, 8]. Considering the products 0much greater than 1 the voltage characteristic is very close to the ideal one [1]. In fact:
05 + 06 2
If the load resistances are not very high compared to the MOS output resistances, the current transfer is given as [1]:
= = 1
1 (1)
+
1+ 1
=
8
7
(7)
3+ 5 ( 03 / 04 )
6 + 5
Considering loads connected to X and Z nodes to be 0 >>1 can be given as:
The parasitic impedance at Y node is given only by the input transistor gate. Its value is easily evaluated knowing transistor
3 6 7 + 4 5 8
sizes and the unitary capacitance of the input gate [1].
= =
5
6
(3
+ 4
) 1 (2)
= 1 1 (8)
If 5 = 7 6 = 9
The impedance level at Y node can be ensured by employing
The X node impedance is inductive. Its resistance part is given by [1]:
2
20(5 + 6)
(9)


SIMULATION RESULTS.
Simulations are carried out in Eldo Spice tool of Mentor Graphics for all circuits for 0.35u and 0.18u for both circuits
and its inductive part is given by:
2
0
20(5 + 6)
(10)
as discussed earlier. Different characteristics are observed.

Simulation results of Class AB CCII based on ifferential pair.
The Z node impedance is high because it is a parallel of two transistor output resistances [1].
= 07 08
07 + 08
(11)

Current Feedback Operational Amplifier (CFOA).
The currentfeedback operational amplifier is positive second generation currentconveyor CCII+ with an additional voltage buffer at the conveyor current output (6,9). The noninverting port (Y) exhibits high impedance to voltage signals where as the inverting port (X) present low impedance to the input current signals. The current at the inverting input (X) of the currentfeedback operational amplifier is transferred to the high impedance currentconveyor output Z, causing a large change in output voltage. The currentfeedback operational amplifier has a transresistance equal to the impedance level at the conveyor Zoutput. Therefore, in the literature, the current feedback operational amplifier is also referred to as a trans impedance amplifier.
The most commercial currentfeedback operational amplifier is AD844, where the user has access to the high impedance node TZ. This amplifier can also be utilized as a second generation current conveyor and current tovoltage converter.
Figure 5: Current feedback OpAmp.
The applications and advantages in realizing active filter transfer function using CFAs have received great attention because the amplifier enjoys the feature of constant feedback independent of closed loop gain and high slew rate besides having low output impedance. Thus it is advantageous to use CFA as a basic building block in the accomplishment of various analog signalprocessing tasks .CFOA offers a higher slew rate, lower distortion, and feedback component restriction. It has a high linearity, constant gain bandwidth product and frequency response is high.
Figure 6: Vx VS Vy.
Figure 7: Ix VS Iz.
Figure 8: Frequency Response of CCII.
Figure 9: Offset.
Figure 10: Linearity between Vx and Vy.
TABLE I: SIMULATION RESULTS FOR CCII BASED ON DIFFERENTIAL PAIR.
Parameters
CCII characteristics simulated value.
0.35um
0.18um
Supply voltage
1.5V
1.8V
Bias current
7uA
4uA
Current gain
1
1
Voltage gain
1
1
Current B.W
90MHz
105MHz
Voltage B.W
190MHz
332MHz
Offset
12mV
35mV
Power Consumption
2.9mV
70uW


CONCLUSION
In this paper CCII based on differential pair is simulated using TSMC 0.18um CMOS technology with 1.8v power supply. Differential pair partially improves for power dissipation and Terminal impedances but bandwidth reduces a when scaled down from 0.35um to 0.18um.CCII can be used as a voltage buffer and current buffer.
REFERENCES

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E. Bruun, A dual current feedback op amp in CMOS current Conveyor, Electron. Lett., vol. 34, pp. 23682369, 2009.

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