Circuits and Systems, 2013, 4, 269-275
http://dx.doi.org/10.4236/cs.2013.43036 Published Online July 2013 (http://www.scirp.org/journal/cs)
Design of Low Voltage, Low Power (IF) Amplifier
Based-On MOSFET Darlington Configuration
Hassan Jassim Motlak
Electrical Department, College of Engineering, Babylon University, Babylon, Iraq
Received April 20, 2013; revised May 21, 2013; accepted May 30, 2013
Copyright © 2013 Hassan Jassim Motlak. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
ABSTRACT
This paper presents a different approach of Intermediate Frequency (IF) amplifier using 0.18 μm MIETEC technology
channel length of MOSFET Darlington transistors. In contrast to Bipolar conventional Darlington pair, a MOSFET
Darlington configuration is employed to reduce supply voltage (VDD) and DC consumption power (Pc). The frequency
response parameters of the proposed design such as bandwidth, gain bandwidth product, input/output noises and noise
figure (NF) are improved in proposed (IF) amplifier. Moreover, a dual-input and dual-output (DIDO) IF amplifier con-
structed from two symmetrical single input and single output (SISO) (IF) amplifier is proposed too. The idea is to
achieve improved bandwidth, and flat response, because these parameters are very important in high frequency applica-
tions. Simulation results that obtained by P-SPICE program are 1.2 GHz Bandwidth (BW), 3.4 GHz (gain bandwidth
product), 0.5 mW DC consumption power (Pc) and the low total output noise is 12 nVHz with 1.2 V single supply
voltage.
Keywords: N(IF) Amplifier; MOSFET Darlington Configuration; Dual-Input and Dual-Output (DIDO) IF Amplifier
1. Introduction
The communication market has been growing very fast
during the last decade especially for mobile communica-
tion systems. The low power, low voltage and low noise
(IF) amplifier is one of the most essential building blocks
in the communication circuits. It can be found in the al-
most of the commercial and military receivers [1]. Sev-
eral architectures of (IF) amplifier such as operational
amplifier and Darlington pairs have been reported [2,3].
The most common used Darlington pair consists of an
emitter-follower and a common-emitter bipolar transis-
tors [3,4]. However, a major drawback is encountered
with its performance. At higher frequencies its response
becomes poorer than that of a single transistor amplifier
[5]. To overcome this problem, a number of modifica-
tions are attempted in Darlington pair amplifiers either
by adding some extra biasing resistances in the circuit or
by using Triple Darlington topology the earlier published
Darlington amplifiers [5-8]. All previous work still suf-
fers from high DC consumption power due to high value
of collector current, high noise and limitation in band-
width. In this paper, a simple circuitry high performance
single input and single output (SISO) (IF) amplifier
based on (0.18 um) channel length MOSFETs Darlington
configuration is proposed. The proposed amplifier used
small channel-length (0.18 μm) to overcome the prob-
lems in consumption power, limitation in bandwidth, and
inter-electrode capacitances. Because the small channel
length of MOSFETs reduced the effect of inter-electrode
capacitances at high frequency operation of MOSFETs.
Besides that the reducing channel length will reduce the
value of threshold voltage of MOSFETs and capable the
designer to use small value of supply voltage and supply
current. A dual-input and dual-output (DIDO) (IF) am-
plifier constructed from two symmetrical (SISO) (IF)
amplifiers is proposed in this approach. The proposed
dual-input and dual output (DIDO) (IF) amplifier is im-
portant in vast area of mobile applications such as multi-
band, wideband, and high-isolation multiple-input multi-
ple-output techniques.
2. Design of Single Input and Single Output
(SISO) IF Amplifier
Figure 1 shows the schematic circuit diagram of the
proposed (IF) amplifier based on MOSFET Darlington
configuration. The proposed amplifier constructed from
two stages using NMOS transistors, biasing voltage and
biasing resistors. The values of biasing resistors includ-
C
opyright © 2013 SciRes. CS

H. J. MOTLAK 270
Figure 1. Schematic diagram of single-stage (IF) amplifier.
ing RG1, RS1, RD2, and RS2 can be calculated using dc
analysis of two stages separately. In this design, the value
of dc consumption power is very important for low
power consideration, so that we have to choose suitable
values of supply voltage VDD and biasing current ID. We
can find the value of aspect ratios 


W
L of two NMOS
transistors using drain current equation for MOSFET as
follows [9]:

2
GST
W
Dn
I
KVV
L

(1)
where, Kn is a channel length modulation parameter, VGS
is the gate to source voltage and VT is the threshold volt-
age of MOSFET transistors.
The change in drain current that will results from a
change in gate-to source voltage can be determined using
the transconductance factor


m
g
in the following ex-
pression:

GST
IW
2
D
mn
GS
g
KVV
VL



 (2)
The transconductance factor is important in calculating
the value of voltage gain, current gain and gain-band-
width product (GBP) of the (IF) amplifier.
The ac small-signal equivalent circuit of the design
configuration is shown in Figure 2. The overall voltage
AV of the small signal equivalent circuit is given by:
 
22 2dD
rR ‖
11 1 mS
gR
22VmD
out1 1
in1 1
1
mS
Vm
mS
VgR
Ag
VgR

 


 (3)
We note that the value of AV depend on the value of
second term of Equation (3), if the value of factor
, the value of overall voltage gain is given by:
A
gR 

(4)
To investigate the effect of the external capacitors
(blocking capacitors

1 and by pass capacitor (CP))
and internal capacitors CGS, CGD, and CDS on frequency
response of the (IF) amplifier in low and high frequen-
cies following expressions of cut off frequencies is used:
2
,CC
1
2π
Leq P
fRC  (5)
In low frequencies the largest cut-off frequency of the
amplifier is determined by bypass capacitor (CP) and
equivalent resistor as illustrated in Equation (5). The
value of equivalent resistor is given by:
1
eq S
m
RR
g
 ‖
(6)
where, Req is the equivalent resistance looking by source
terminal of MOSFET in (IF) amplifier .
The analysis of the high-frequency response of the
proposed (IF) amplifier using high frequency equivalent
circuit is shown in Figure 3.
1) The cut-off frequency of the overall voltage gain for
the input circuit is defined by following expression:
1
1
2π
Hi Thi in
fRC 
R
C
(7)
where Thi is the Thevenins resistance of input circuit
and 1in is the total input capacitance included inter
electrode


GS wi
2) The cut-off frequency of the overall voltage gain for
the output circuit is defined by following expression:
C

C and wiring capacitance .
1
1
2π
Ho Tho ou
fRC  (8)
where RTho is the Thevenins resistance of output circuit
and Co is the total output capacitance included inter elec-
trode capacitance (CGD) and wiring capacitance (Cwo).
From Equations (7) and (8), we note that the inter-
electrode capacitances of MOSFET transistors are play
important role in determining the frequency response of
(IF) amplifier in high frequencies. These capacitances
defined by gate dimensions of MOSFET, so that we can
extend the value of upper-cut-off frequency by suitable
choose of technology 0.18 μm channel-length of MOS-
FET. Our design confirms this concept as we see in
simulation results. The gate dimensions of NMOS tran-
sistors and biasing currents of the proposed (IF) amplifier
are given Table 1.
3. Design of Dual-Input, Dual-Output (DIDO)
(IF) Amplifier
The dual-input, dual-output (DIDO) (IF) amplifier plays
important role in several mobile applications such as
multiband, wideband, and high-isolation multiple-input
multiple-output techniques [10]. The proposed (DIDO)
(IF) amplifier is based on simple circuitry approach with
high performance parameters compared with conven-
ional amplifiers. The design idea of proposed dual-input t

H. J. MOTLAK 271
Figure 2. Small-signal equivalent circuit of MOSFET Darlington configuration.
Figure 3. High frequency ac equivalent circuit for proposed (IF) amplifier.
Table 1. Gate dimensions and biasing currents of MOSFETs for proposed (SISO) (IF) amplifier in Figure 1.
Gate dimensions and basing currents
Transistor’s number Gate width
W (μm)
Channel length
L (μm)
Biasing current
(μA)
M1 1.75 0.18 17.6
M2 1.75 0.18 396.3
(DIDO) (IF) amplifier based on constructed two sym-
metrical single (IF) amplifier using face-to-face connec-
tion as shown in Figure 4.
4. Simulation Results
The frequency response of the proposed amplifier that
characterized by flat voltage gain and wide bandwidth is
shown in Figure 5, where the maximum value of the
voltage gain is 7.6 dB. Figure 6 shows the phase re-
sponse of the voltage gain. The input and output noises
of the proposed (IF) amplifier is shown in Figure 7. As
can be seen in measurement, values of input/output
noises are increased with increasing the frequency of
output voltage and current but still in acceptable range
due to high noise immunity of MOSFET technology that
used in proposed (IF) amplifier. The value of output cur-
rent delivered to the resistive load used in proposed (IF)
amplifier is decreased as RL varied from 10 kΩ to 100
kΩ. The value of output current is varied from 560 μA to
10 μA as load resistor is varied from 10 kΩ to 100 kΩ as
can be seen in Figure 8.
Figures 9 and 10 show the frequency response (phases)
and (magnitudes) of the dual-input and dual-output (DIDO)
(IF) amplifier. We note that the frequency response in
same values for both outputs (positive and negative) with
phase difference is 180˚. Moreover, the transient time
response shown in Figure 11 of DIDO (IF) amplifier for
both outputs (positive and negative) are in same value
with phase difference is 180˚ too. Figures 9-11 prove
that the DIDO (IF) amplifier operates as we expected in
theoretical background.
Figure 12 shows the harmonic measurements of
DIDO (IF) amplifier. In this figure, the value of har-
monic distortion is increased due to increasing in fre-
quency. To decrease the effect of harmonic distortion
source degeneration technique can be used.
Table 2 shows the performance parameters of the pro-
posed (IF) amplifier compared with other designs in pre-
vious works. The simulation results of the proposed am-
plifier verify the excellent improvement in dc consump-
tion power, and low supply voltage.

H. J. MOTLAK 272
Figure 4. Schematic diagram of DIDO (IF) amplifier.
Figure 5. Frequency response (magnitude of voltage gain) of single (IF) amplifier.
Figure 6. Frequency response (phase of voltage gain) of single (IF) amplifier.

H. J. MOTLAK 273
Figure 7. Input and output noises of proposed (IF) amplifier.
Figure 8. Frequency response of output current as RL is varied from 10 kΩ to 100 kΩ of the prosed (IF) amplifier. op
Figure 9. Frequency responses (phases) of positive and negative outputs of the proposed DIDO (IF) amplifier.

H. J. MOTLAK 274
Figure 10. Frequency responses (magnitude) of positive and negative outputs of the proposed DIDO (IF) amplifier.
Figure 11. Transient response of positive and negative outputs of the proposed DIDO (IF) amplifier.
Figure 12. 3HD measurement of positive and negatives outputs of the proposed DIDO (IF) amplifiwith different frequen-er
cies of input voltages.

H. J. MOTLAK 275
ized the performance parameters of the proposed (IF) amplifier compared with previous designs.
Previous work compared with proposed (IF) amplifier
Table 2. Summar
Performance parameters
(IF) amplifier proposed mplifier of Figure 1 by [7] (IF) amplifier proposed by [6] (IF) a
Technology PHEMT FETs 2-μm GaAsHBT BJTs (0.18 μm) MOSFET
GBP (GHz) 1.0 19.0 3.0
Volta dB)
C
ge Gain (Av) (15.5 12.8 7.6
Supply voltage VDD (V) 5.0 10.0 1.2
onsumption power (mW)500 150 0.5
Noise Figure (NF) (dB) 2.0 _ 5.6

ngle output low voltage and low
[1] El-S. A. M. H
5. Conclusion
Single input and si
power (IF) amplifier based on Darlington configuration
is designed in this work. Minimum channel length (0.18
μm) of MOSFET Darlington transistors is used to im-
prove the performance of MODFETs in high frequency
operation, and to reduce the effects of parasitic capaci-
tance of MOSFETs in high frequency operation. More-
over, the decreasing of channel length of MOSFETs re-
duces the value of power supply of the circuit and the
consumption power because the threshold voltage of
MOSFETs has become smaller. A dual-input and dual
output (DIDO) (IF) amplifier constructed from two
symmetrical single input single output (IF) amplifier is
also proposed in this paper. A wide bandwidth around
(1.2 GHz), wide gain bandwidth product around (3.0
GHz), low supply voltage (1.2 V), and low consumption
power around (0.5 mW) are achieved in this proposed
design. The drawback of this design is low voltage gain
around (7.6 dB), but it can be increased using feedback
technique or using triple stage Darlington configuration.
REFERENCES
asaneen and N. Okely, “On-Chip Inductor
Technique for Improving LNA Performance Operating at
15 GHz,” Circuits and Systems, Vol. 3, No. 4, 2012, pp.
334-341. doi:10.4236/cs.2012.34047
[2] P. Kakoty, “Design of a High Frequency Low Voltage
CMOS Operational Amplifier,” International Journal of
VLSI Design & Communication Systems (VLSICS), Vol. 2,
No. 1, 2011, pp. 73-85. doi:10.5121/vlsic.2011.2107
[3] A. Motayed and S. N. Mohammad, “Tuned Performance
of Small-Signal BJT Darlington Pair,” Solid-State Elec-
tronics, Vol. 45, 2001, pp. 369-371.
doi:10.1016/S0038-1101(00)00247-1
lifier Design Tech-
data.eefocus.com/myspace/0/2029/bbs/1192675584
d S. Srivastava, “Small-Signal Amplifier
g and C.-H.
mediate Fre-
N.
[4] C. Arnott, “Wideband Gain Block Amp
niques,” Applied Microwave & Wireless, 2001, pp. 98-
109.
http://
/23b66dea.pdf
[5] S. N. Shukla an
with Three Dissimilar Active Devices in Triple Darling-
ton Topology,” International Journal of Advanced Re-
search in Electrical, Electronics and Instrumentation En-
gineering, Vol. 1, No. 6, 2012, pp. 502-508.
[6] C.-S. Lin, M.-D. Tsai, H. Wang, Y.-C. Wan
Chen, “A Monolithic HBT Broadband Amplifier Using
Modified Triple Darlington Configuration,” 12th GAAS
Symposium, Amsterdam, 2004, pp.331-334.
[7] H. Cebi, “A High Linearity Darlington Inter
quency (IF) Amplifier for Wide Bandwidth Applications,”
Microwave Journal, Vol. 53, No. 11, 2011, pp. 18-24.
[8] A. M. H. Sayed ElAhl, M. M. E. Fahmi and S.
Mohammad, “Quantitative Analysis of High Frequency
Performance of Modified Darlington Pair,” Solid-State
Electronics, Vol. 46, No. 4, 2002, pp. 593-595.
doi:10.1016/S0038-1101(01)00308-2
[9] R. L. Boylestad, L. Nashelsky and F. J. Monssen, “Elec-
and T.-Y. Yun, “Small
tronic Devices and Circuit Theory,” 8th Edition, Prentice
Hall, Upper Saddle River, 2002.
[10] S.-H. Kim, Z.-J. Jin, Y.-B. Chae
Internal Antenna Using Multiband, Wideband, and High-
Isolation MIMO Techniques,” ETRI Journal, Vol. 35, No.
1, 2013, pp. 51-57. doi:10.4218/etrij.13.0112.0183