Download Comparative analysis of different Current mirror using

ISSN: 2277 – 9043
International Journal of Advanced Research in Computer Science and Electronics Engineering (IJARCSEE)
Volume 3, Issue 6, June 2014
Comparative analysis of different
Current mirror using 0.35µm and its
Application
Rashmi Sharma#1, Mr. Neeraj Gupta #2 , Mr. Ashok kumar #3
#1
#2,#3
M.Tech (ECE), Amity University Gurgaon
Lecturer, Amity University Haryana (gurgaon),India
Abstract— Current mode circuits have come to
knowledge as compared to voltage mode circuits in
recent days because of their properties like low voltage
requirement, high slew rate and wider bandwidth The
circuit made by current mode technique uses small
area, consumes less power dissipation and achieves
high operation speed. Current mirrors are the main
structures of almost all analog circuits. Current mirror
provides high performance, low voltage and low power
consumption to its circuits. In the first section of this
paper we will analyze and compare the performance
parameters of different current mirrors in 350 nm
technology in Xilinx xmanager (mentor graphics) tool
and in the other section we will show its application in
analog circuits. The performance parameters are
output impedance, power dissipation, threshold voltage
and Trans conductance.
Keywords— Current mirror, current mode circuits, input
the input current constant regardless of drive conditions.
Under ideal conditions, the current-mirror gain is
independent of input frequency, and the output current is
independent of the voltage between the output and
common terminals. The transistors used must be identical
and the gate to source voltage should be equal and
transistors should work in saturation region. When used
as a load element in transistor amplifiers, the high
incremental resistance of the current mirror results in
high voltage gain at low power supply voltages[1].
and output compliance voltage.
Output compliance voltage
To keep output transistor in saturation, the minimum
voltage that is required is called output compliance
voltage. This value can be different for different current
mirror structures. For a simple current mirror
1.
Introduction
Current mirrors made by using active devices have come
to be widely used in analog integrated circuits both as
biasing elements and as load devices for amplifier stages.
The circuit made by current mode technique uses small
area, consumes less power dissipation and achieves high
operation speed. The current mode circuits uses current
signal both at input and output. When the current mirror
is used as a load element in amplifiers, the high
incremental resistance of current mirror provides high
voltage gain at very low supply voltage.
The current mirror uses the principle that if the gatesource potentials of two identical MOS transistors are
equal, then the current flown through their Drain
terminals should be the same[15]. The use of current
mirrors in biasing can result in superior insensitivity of
circuit performance to variations in power supply and
temperature [1].
2. Current Mirror
A current mirror is a two terminal circuit in which the
input current is mirrored or copied from the input
terminal to output terminal and this output current is
independent of the voltage applied to the output
terminals. An important feature of the current mirror is
its high output resistance which keeps the output current
constant regardless of load conditions. Another feature of
the current mirror is its low input resistance which keeps
The common application of current mirrors are as active
load, as biasing element, current amplifier, operational
amplifier, analog to digital converters, digital to analog
converter and current conveyor etc[3]. There are many
current mirrors available, following are the performance
parameters of a current mirror:
minimum voltage required is Vds2 (sat).
Input and output impedance
CM should have zero input and infinite output
resistance so that the input voltage will not vary
with the input currents and the output currents will
not depend on the applied output voltage. Output
resistance is very important parameter for a current
mirror. [12]
Device matching
It requires perfect matching of the mirroring
transistors Ml and M2 (Fig. 1) for accurate
mirroring of the signal current. Current transfer
ratio (CTR) is precisely set by the (W/L) ratios.[12]
Input linear range
The total input current must be in the range where
both transistors (Ml and M2) operate saturations.
DC balance
The drain source voltage of the mirror transistors
MI and M2 should be equal. The error due to the
mismatch in drain to source voltages is λ(Vds2-
317
All Rights Reserved © 2014 IJARCSEE
ISSN: 2277 – 9043
International Journal of Advanced Research in Computer Science and Electronics Engineering (IJARCSEE)
Volume 3, Issue 6, June 2014
Vds1), where λ is the channel length modulation
coefficient.
3.
Different current mirrors
1.Simple current mirror: Figure 2 shows an MOS
version of the simple current mirror. The drain-gate
voltage of M2 is zero; therefore, the channel does not
exist at the drain, and the transistor operates in the
saturation or active region if the threshold is positive.
Although the principle of operation for MOS transistors
does not involve forward biasing any diodes, M2 is said
to be diode connected in an analogy to the bipolar case.
Assume that M1 also operates in the active region and
Fig 2: Simulated wave for simple current mirror
that both transistors have infinite output resistance. Then
2.Cascode current mirror:
ID1 is controlled by VGS1, which is equal to VGS2 by KVL.
resistance is a good measure of the perfection of the
A KVL equation is at the heart of the operation of all
current mirror[cm1]. Higher performance current mirrors
current mirrors. If the transistors are identical, (W/L)2 =
try to increase the value of Rout. To increase the output
(W/L)1, and therefore
resistance the approach used is Cascode structure.
The small signal output
IOut = ID1 = ID2
Cascode CM shown in Fig 4 is a good choice for
The above equation shows that the current that flows in
increasing output resistance. The small-signal output
the drain of M2 is mirrored to the drain of M1. Since βF
resistance is
→∞ for MOS transistors, and KCL at the drain of M2
yield
Ro = ro2[1 + (gm2 + gmb2)ro1] + ro1
The bipolar Cascode current mirror cannot realize an
IOUT = ID1 = IIN
output resistance larger than β0ro/2 because β0 is finite
and nonzero small-signal base current flows in the
Cascode transistor. In contrast, the MOS Cascode is
capable of realizing high output resistance by increasing
the number of stacked Cascode devices because β0→∞
for MOS transistors. However, the MOS substrate
leakage current can create a resistive shunt to ground
from the output node, which can dominate the output
resistance for VOUT > VOUT (min).
Fig 1: Simple current mirror circuit
Simulation Results of Basic Current Mirror:
Fig 3: Cascode current mirror circuit
318
All Rights Reserved © 2014 IJARCSEE
ISSN: 2277 – 9043
International Journal of Advanced Research in Computer Science and Electronics Engineering (IJARCSEE)
Volume 3, Issue 6, June 2014
Simulation Results of Basic Current Mirror:
Fig 4: Simulated result for Cascode current mirror
3.Wilson current mirror: Wilson current mirror use
Shunt-series negative feedback technique to improve the
output impedance and stabilize the output drain current
[10]. The process for Wilson current mirror design
involves matched identical transistor M1& M3 to achieve
same drain current.
Simulation Results of Wilson Current Mirror:
Fig 6: Simulated result for Wilson current mirror
4. Simulated results
The following table shows the simulated and calculated
parameters of the different current mirror:
Table 1: Comparison of different current mirrors
Parameter
Simple
Cascode
Wilson
CM
CM
CM
Slew rate
5.1706u
58.874u
104.82u
Maximum
61.00u
49.721u
44.903u
Power
38.1050u
139.5324u
15.1295u
dissipation
W
W
W
Threshold
350.96mV
325.60mV
380.50mV
414kΩ
2.40MΩ
4.50MΩ
99.50u
90.40u
310.50u
5v
1.8v
5v
0.35um
0.35um
0.35um
2
4
3
voltage
Output
impedance
Trans
conductance
Supply
voltage
Simulation
Fig 5: Wilson current mirror circuit
The drain current curve with respect to output is much
more flat than that for Cascode and simple current
mirror. Thus provides better linearity to the output
response. Output impedance is higher thus provides
better mirror efficiency[9].
technology
Number of
transistors
From the above table it is clear that performance wise the
Wilson current is best than the other two current mirrors
because the power dissipation is very small and other
parameters are also high as compare to others.
319
All Rights Reserved © 2014 IJARCSEE
ISSN: 2277 – 9043
International Journal of Advanced Research in Computer Science and Electronics Engineering (IJARCSEE)
Volume 3, Issue 6, June 2014
6.
Application
Many configurations of current mirror are
discussed and used for many applications.
Especially Wilson current mirror which is one of
the main building blocks of analog and mixed
signal integrated circuits for low voltage design
circuit and high speed application. The Wilson
current mirror can be used for application to Linear
Voltage-to-Current Converter Used for Two-Stage
Operational Amplifier[14]. Fig 8. Shows the circuit of
voltage to current converter used for Op amp application:
7. Conclusion
In this article we have simulated and analyzed the
different types of current mirrors and successfully
measured the parameters of current mirrors using DC
analysis. Any one of them can be selected as per their
requirement. We have compared the performance of
simple CM, Cascode CM and Wilson CM. It is
concluded from the table that the Wilson current mirror
is best among them because of its medium output
compliance voltage and high output resistance. Wilson
current mirror can be used as a low biasing circuit.
Circuit diagram:
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ISSN: 2277 – 9043
International Journal of Advanced Research in Computer Science and Electronics Engineering (IJARCSEE)
Volume 3, Issue 6, June 2014
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321
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