‫مجلة الجامعة األسمرية للعلوم األساسية والتطبيقية‬

‫م‬7132 ‫ ديسمبر‬، ‫ الجزء الثاني‬،)13( ‫العدد‬

A NEW CMOS DESIGN AND ANALYSIS OF CURRENT

CONVEYOR SECOND GENERATION (CCII)

MAHMOUD AHMED SHAKTOUR1, FATHI OMAR ABUBRIG2, AlAA YOUSEF OKASHA3

1
Elmergib University, Faculty of Science, Department of Physics.
2
Al- Asmarya Islamic University, Faculty of Science, Department of Physics.
3
Elmergib University, Faculty of Science, Department of Physics.

1
mashakture@elemergib.edu.ly, 2dr.Fathomar@gmail.com, 3alaa_okasha2000@yahoo.co.uk

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 Op-amp 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
The proposed current conveyors are simulated using TSMC 0.18μm CMOS technology on
Advanced Design System and the results are also tabulated for comparison. The main features
of these current conveyors are low voltage, less power, high slew rate and wide bandwidth for
voltage transfer (Vy to Vx) and current transfer (Ix to Iz) which make them suitable for high
frequency and low power applications.

Keywords: Bulk-Driven transistors, Current Conveyor of Second Generation CCII, CMOS

integrated circuit, PSPICE simulation.

1. INTRODUCTION

One of the most basic building blocks in the area of current-mode analogue signal
processing is the current conveyor (CC).The principle of the current conveyor of the first
Generation was published in 1968 by K. C. Smith and A. S. Sedra [1]. Current Conveyor First
Generation CCI was then replaced by a more versatile second-generation device in 1970 [2],
the CCII Current conveyor designs have mainly been with BJTs due to their high
transconductance values compared to their CMOS counterparts. They are used as current-
feedback operational amplifiers like the MAX477 high-speed amplifier and the MAX4112

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 ‫مجلة الجامعة األسمرية للعلوم األساسية والتطبيقية‬
‫م‬7132 ‫ ديسمبر‬، ‫ الجزء الثاني‬،)13( ‫العدد‬
low-power amplifier, which both feature current feedback rather than the conventional
voltage feedback used by standard operational amplifiers. Current conveyors are used in high-
frequency applications where the conventional operational amplifiers can not be used,
because the conventional designs are limited by their gain-bandwidth product.
The current mode circuits such as Current conveyors (CCs) have received considerable
attention and emerged as an alternate building block to the Op-Amp (voltage mode circuit) in
the field of analog signal processing [3] due to its potential performance feature. In CCs, the
use of current rather than voltage as the active parameter can result in a higher usable gain,
accuracy and bandwidth due to reduced voltage excursion at sensitive nodes [4]. The current
conveyors are not only useful for current processing, but also offer certain important
advantages in voltage processing circuits. The nonlinear circuits and dynamics [5] can easily
be developed using CCs.
With the reduction in the supply voltage and device threshold voltage of CMOS technology,
the performance of CMOS voltage mode circuits has greatly affected which results in a
reduced dynamic range, an increased propagation delay and reduced noise margins. The CCs
have simple structure, wide bandwidth and capability to operate at low voltage. It also offer
unity current gain, unity voltage gain, higher linearity, wider dynamic range and better high
frequency performance.

2. THE CURRENT CONVEYOR CC

The current conveyor is functionally flexible and versatile in nature as it has precise unity
voltage gain between X and Y; unity current gain between Z and X as shown in Fig. 1, rather
than the high ill-defined open loop gain of Op-Amps. Because of this fact, CCII is generally
used without feedback in amplifier applications [6, 7].

IY
IZ
VY Y CC Z VZ
X

IX

VX

Fig. 1: Building block of Current conveyor

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 ‫مجلة الجامعة األسمرية للعلوم األساسية والتطبيقية‬
‫م‬7132 ‫ ديسمبر‬، ‫ الجزء الثاني‬،)13( ‫العدد‬

The build block of current conveyor and its generalised characteristics equation are
represented by the following hybrid matrix.

(1)

The current conveyor is a grounded three-port network represented by the black box (Fig
1) with the three ports denoted by X, Y, and Z. Its terminal characteristics can be represented
best by a hybrid matrix giving the outputs of the three ports in terms of their corresponding
inputs [8].

3. CURRENT CONVEYOR SECOND GENERATION CCII

The second-generation current conveyor (CCII) is used as a basic building block in many
current-mode analog circuits. It offers high input impedance at voltage input port Y, which is
preferable in order to avoid loading effect. Therefore, second generation current conveyor is
developed to overcome the problem loading effect of CCI. The CCII is considered as a basic
building block in analog circuit design because all the analog applications can be developed
by making suitable connections of one or more CCIIs with passive and active components.
The second-generation current conveyor is a grounded three-terminal (X, Y and Z) device
as shown in Fig. 2 (a), and the equivalent circuit of the ideal CCII is shown in Fig. 2 (b).

IY IZ
VY Y VY 1 VZ
IZ
CCII Z VZ

VX X
IX
VX

(a) (b)
Fig. 2: (a) The CCII symbol, (b) ideal equivalent circuit.

The characteristics of ideal CCII are represented by the following hybrid matrix

(2)

An ideal CCII has the following characteristics:

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 ‫مجلة الجامعة األسمرية للعلوم األساسية والتطبيقية‬
‫م‬7132 ‫ ديسمبر‬، ‫ الجزء الثاني‬،)13( ‫العدد‬
 Infinite input impedance at terminal Y (RY = ∞ and IY = 0)
 Zero input impedance at terminal X (RX = 0)
 Accurate voltage copy from terminal Y to X (VX = VY)
 Accurate current copy from terminal X to Z with infinite output impedance at Z (IZ =
IX and RZ = ∞)
4. OPERATIONS USING THE IDEAL CCII

 Amplifiers using CCII

The CCII can easily be used to form the current output amplifiers and voltage-output amplifier
as shown in Fig. 3.The voltage- and current- gains are as follows:

(3)

(4)

Iin Vin
Y Y
Iout CCII Z
CCII+ Z Y
IX X CCII Z
X IZ
IX X
Vout
R1 R2 R1 R2

(a) (b)

Fig. 3: (a) CCII-based current amplifier, (b) CCII-based voltage amplifier.

 Integrators using CCII

In Fig. 4, simple current- and voltage- integrators are presented.

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 ‫مجلة الجامعة األسمرية للعلوم األساسية والتطبيقية‬
‫م‬7132 ‫ ديسمبر‬، ‫ الجزء الثاني‬،)13( ‫العدد‬
Iin
Y Vin Y
Iout
CCII+ Z CCII Z Y
IZ Z
X IX X CCII
Vout
X
R R C
C

(a) (b)
Fig. 4: (a) CCII-based current integrator, (b) CCII-based voltage integrator.

The output signals are as follows:

(5)

(6)

 Adders using CCII

In Fig. 5, CCII-based current adder and CCII-based voltage adder are reported, with the
following equations:

R2 I2
Vin2
Iin1
I1
Vin1 X
X Iout R1
Iin2 CCII Z Y
CCII Z Y IZ
Y Vout CCII Z
X
R

(a) (b)

Fig. 5: (a) CCII-based current adder, (b) CCII-based voltage adder.

(7)

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 ‫مجلة الجامعة األسمرية للعلوم األساسية والتطبيقية‬
‫م‬7132 ‫ ديسمبر‬، ‫ الجزء الثاني‬،)13( ‫العدد‬

(8)

 Differentiators using CCII

Current- and voltage-mode versions are shown in Fig. 6. The output signals are as follows:

Iin Vin Y
Y Iout CCII Z Y
CCII Z
X CCII Z
X IX IZ
X
Vout
R C C R

(a) (b)

Fig. 6: (a) CCII-based current differentiator, (b) CCII-based voltage differentiator.

5.PROPOSED CMOS CURRENT CONVEYOR SECOND GENERATION

A new connection of Bulk-driven OTA is used to realize the CCII. In the OTA-based
approach, presented in Fig.7, Bulk-driven OTA is used to implement the unity gain buffer
between the Y and X inputs [9].The X input current Ix is sensed by duplicating buffers, output
transistors M6 and M7 using transistors M8 and M9, and extracting the X current from them as
Iz. Since transistors M8 and M9 have the same size and gate-source voltage as the output stage
transistors M6 and M7, the current Iz should be a copy of the current flowing through M6 and
M7 which is Ix. Transistors M10-M15are used to generate Iz. Since no additional transistors
need to be inserted between the OTA and rails, the approach will not increase the minimum
operating voltage over that of the operational core. In addition the voltage follower is based
on an OTA, thus it will maintain all the benefits and also the disadvantages of such a circuit
i.e. a good voltage follower at the cost of lower bandwidth [10].

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 ‫مجلة الجامعة األسمرية للعلوم األساسية والتطبيقية‬
‫م‬7132 ‫ ديسمبر‬، ‫ الجزء الثاني‬،)13( ‫العدد‬
VDD

M13 M15
Vbias M7 M9 M11
M5
M16
Z+

X Y
Vbias1 Z-
R CC
Vbias1 M1 M2
RC

M6 M8 M10 M12 M14

M3 M4
M17

VSS
Fig. 7: Bulk-driven CCII± based on Bulk-driven OTA.

The aspect ratios of each of the transistors used the CCII in Fig. 7 are listed in Table1.

VDD& VSS = ±0.6V, R = 5kΩ, RC = 4.7kΩ, CC = 0.5pF

Transistor Length (µm) Width (µm)

M1,M2 2 30
M3,M4 2 4
M5,M16 3 20
M6, M8, M10,M12, M14 2 16
M7, M9, M11,M13, M15 3 40
M17 3 10

Table 1. Aspect ratios of the transistors used in the CCII in Fig. 7.

6. SIMULATION RESULTS
The simulated frequency responses of current gains Iz+/Ix, Iz-/Ix are given in Fig. 8. The cut
off frequencies for the gains are 20 MHz and 52 MHz, respectively.
In Fig. 9, the input voltage buffer behaviour is shown. A DC sweep simulation has been
performed, to check the range in which the voltage on X node is equal to the voltage applied
to Y node.

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 ‫مجلة الجامعة األسمرية للعلوم األساسية والتطبيقية‬
‫م‬7132 ‫ ديسمبر‬، ‫ الجزء الثاني‬،)13( ‫العدد‬
The current linearity between X and Y terminal of the bulk-driven current conveyor
(CCII±) from Fig. 7, is demonstrated in Fig. 10. Note that for input currents Ix and Iz, the
boundary of linear operation is ca±16μA.
The corresponding small-signal current gains are as follows: Iz+/Ix, Iz-/Ix = 1, and the
corresponding voltage gain Vx/VY = 0.97.
The small-signal low frequency resistance of the X terminal Rx is equal to 166Ω as shown
in Fig. 11. The small-signal resistance of the Y terminal RY is equal to 50GΩ.
The small-low frequency signal resistances of the Z+, Z- outputs terminals are equal to
560kΩ, and 554kΩ, respectively. Simulation results of the CCII± are summarized in Table 2.

10 600mV
VY[V]
5 400mV
Iz+/Ix
0 200mV
Iz-/Ix
-5 0mV

-10 -200mV

-15 -400mV
1.0Hz 100Hz 10KHz 1.0MHz 100MHz -600mV -200mV 0mV 200mV 600mV
Current gain [dB] Frequency [Hz] Vx[V]

Fig. 9: Voltage follower between X and Y of the

Fig. 8: Frequency variation of the current gains Iz+/Ix, CCII in Fig. 7.
Iz-/Ix in dB of the CCII in Fig. 7.

16uA

10uA
IZ[A]
0A

-10uA

-16uA
-16uA -8uA 0A 8uA 16uA
Ix[A]
Fig. 10: Current linearity between X and Y of the CCII in Fig. 7

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 ‫مجلة الجامعة األسمرية للعلوم األساسية والتطبيقية‬
‫م‬7132 ‫ ديسمبر‬، ‫ الجزء الثاني‬،)13( ‫العدد‬
24 600K
K
2 RZ+- [Ω] rinZ+
0
1 400K
K
Rx[Ω]
5
K
10 rinZ-
K 200K
5
K
0 0
1.0H 10Hz 1.0KH 100KH 10MH 1.0GH 1.0Hz 100Hz 10KHz 1.0MHz 100MHz
z z Frequency
z [Hz]
z z Frequency [Hz]

Fig. 11: The X node input resistance rin,x of the CCII Fig. 12: The Z node output resistance rin,Z
in Fig. 7. of the CCII in Fig. 7.

Characteristics Simulation Result

Power consumption 119 μW
3-dB bandwidth IZ+/IX 20 MHz
3-dB bandwidth IZ-/IX 52 MHz
DC voltage range -400, 600 mV
DC current range ±16 µA
Current gain IZ/IX 1
Voltage gain VX/VY 0.97
Node X parasitic DC resistance 166 Ω
Node Y parasitic DC resistance 50 GΩ
Node Z+ parasitic DC resistance 560 kΩ
Node Z- parasitic DC resistance 554 kΩ
Measurement condition: VDD = 0.6V, VSS = - 0.6V

Tab. 2: Simulation results of the Bulk-driven CCII.

7. CONCLUSION
In this paper Bulk-driven CCII based on operational Transconductance Amplifier OTA is
simulated using TSMC 0.18um CMOS technology with 0.6V power supply. Differential pair
partially improves for power dissipation and terminal impedances but bandwidth reduces
when scaled down from 0.35um to 0.18um. CCII can be used as a voltage buffer and current
buffer.

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 ‫مجلة الجامعة األسمرية للعلوم األساسية والتطبيقية‬
‫م‬7132 ‫ ديسمبر‬، ‫ الجزء الثاني‬،)13( ‫العدد‬
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[2] CHUN-MINGCHANG. "Multifunction biquadratic filters using current conveyors".,

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[3] R V Yenkar, R S Pande and S S Limaye. "The Survey of Historical - Technical

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[6] Sedra A, Robert G, Gohn F S: The current conveyor: history and progress, IEEE
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[7] Grigorescu L, "Amplifier built with current conveyors", Rom. Journ. Phys., 2008, 53(1-
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[8] Senani R, "Novel application of generalized current conveyor", Electronics Letter,

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[9] KHATEB, F., BIOLEK, D., NOVACEK, K. "On the design of low-voltage low-power
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[10] Shaktour, M. "Design of low power low voltage bulk driven operational
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