DESIGN OF 2.4 GHZ MMIC FEED FORWARD AMPLIFIER FOR WIRELESS APPLICATIONS

International Journal Of Microwave Engineering (JMICRO) Vol.5, No.2, April 2019
DOI : 10.51 21/Jmicro.2019.5201 1
DESIGN OF 2.4 GHZ MMIC FEED FORWARD
AMPLIFIER FOR WIRELESS APPLICATIONS
P.Shanthi1
and J.S.Baligar2
1
Department of Telecommunication Engineering, R.V.College of Engineering,
Bengaluru, India
2
Department of Electronics & Communication, Dr.AIT, Bengaluru, India
ABSTRACT
This paper proposes a design of 0.15μm Monolithic Microwave Integrated Circuit (MMIC) power amplifier
using GaAs pHEMT technology at 2.4 GHz which employs feed forward linearization technique to improve
linearity. The amplifier is designed to operate in personal communication systems (PCS) frequency range
using WIN semiconductor GaAs pHEMT technology. Single stage power amplifier is designed in lumped
and distributed components with its layout. Linearity of PA is improved by Feed forward Linearization
technique. To evaluate the performance of proposed linearized amplifier, Advanced Design system (ADS)
tool is used. The designed circuit results with 13.65dBm output power at 1dB compression point (P1dB),
6dB power gain and maximum Power added efficiency of 16.4%. Linearity achieved by feed forward
linearizer circuit with third order intermodulation suppression of 30dBc for the output power level of
8.217dBm and 1dB compression point at an input power of 15 dBm whereas 6 dBm for the Power amplifier
without feed forward linearizer circuit. The designed Power amplifier system with feed forward linearizer
had IMD3 suppression of 30dBc which is in appreciable range with improvement in 1dB compression
point.
KEYWORDS
Power amplifier, Feed forward, Intermodulation, Third order Intermodulation, Power added Efficiency
1. INTRODUCTION
The performance of a wireless system over which the communication takes place is decided
based on transmitter; receiver and communication medium. The nonlinear elements used for a
linear purpose will generate nonlinear distortion which leads to spectral regrowth. The design of
PA linearizing and efficiency improvement schemes, and architectures is attracting much
attention in recent years. The attempts to reduce the effective PA compression and phase
variation effects to meet air interface specifications, while maximizing the PA efficiency is being
carried on. Few Included among them are feed forward, envelope elimination and restoration
(EER), Cartesian feedback, and Pre distortion techniques. A feed-forward mitigation algorithm
with an adaptive filter implemented and applied real time measurements [1],To improve better
efficiency and linearity, PA linearization technique is inevitable[2].
The paper [3] discussed a feed forward linearization technique implemented on a PA at 2 GHz
which results with third order intermodulation suppression of 108dBm. A new technique explored
with a combination of feed forward and predistortion method results with better linearity [4].
Linear and wide band characteristics by feed forward linearization technique achieved, where the
circuitry is complex with an auxiliary error amplifier and passive control circuits [5]. The author
discusses the Modified quasi memory less nonlinear Saleh model for implementation of power
amplifier which is done using Simulink [6]. The paper [7] executed a feed forward amplifier with

2
adaptive network implemented using Advanced design systems for wireless communication
applications. An ANN based controller is trained to handle all the mappings associated with the
inputs and the corresponding outputs associated with all the controllers of the UPFC [8].
Simulations are performed in the MATLAB / SIMULINK environment. Feed forward
Linearization techniques results in higher level of intermodulation cancellation of all products
with wider bandwidths and stability over other linearization methods.
A methodology for precise balance of amplitude and Phase with the loops of feed forward
amplifier is exhibited for perfect intermodulation cancellation. The implementation of digital
control of feed forward amplifiers reduces the sensitivity to amplitude or phase shift [9].
2. FEED FORWARD SYSTEM
A typical feed forward system as in Figure1 involves two loops. The first loop is signal
cancellation loop which samples input signal by a coupler which then amplified by the main
amplifier with a time delay.
Figure1. Feed forward system
Feed forward was invented for distortion reduction in amplifiers by Black. The second loop
called distortion cancellation loop comprises of an error amplifier, couplers and delay element.
The input signal is splitted into two identical signals by power splitter, with one signal directed to
main PA while the other signal enters a delay component. The upper path signal is amplified by
the main amplifier whose inherent nonlinearity results in intermodulation components. This
signal is sampled and attenuated by attenuator and then added with delayed input signal. The gain
of error amplifier decides amplification factor which cancels out the distortion components
present in main amplifier output. The directional coupler is fed with error amplifier output. This
coupler is fed with another input which is the delayed main-path signal both in time and phase.
The cancellation accuracy of the main signal in the first loop and error signal cancellation from
the output of coupler-combiner determines the quality of operation of the linearizer system.
Higher linearity is achieved when the insertion losses of power splitters and combiners total about
30% of output power of PA.
The equation that describes the output of Feed forward linearizer is,
𝑉𝑜𝑢𝑡( 𝑡) =
𝐴1
2
𝑉𝑖𝑛( 𝑡) 𝑒−𝑗𝜔(𝜏1+𝜏2)
(1)

3
Where A1 is the main power amplifier gain,τ1 and τ2 is the delay associated with main power
amplifier and error amplifier and Vin is the input signal.
A variable phase shifter is used to adjust the phase of PA output by taking the input reference.
The delay line in error cancellation branch is used to achieve wider bandwidth and takes care for
main amplifier group delay by time aligning the main power amplifier output and reference
signal.
2.1. DESIGN OF POWER AMPLIFIER
The pHEMT technology provides excellent low-noise properties due to high transconductance
and better electron mobility. Power amplifier is designed using 0.15µm GaAs pHEMT.
Transconductance Gm is increased by proper choice of biasing point which improves gain of PA.
The bias point is selected from transfer characteristics, at Vds of 3V and Vgs of 0V, with drain
current of 398mA. Figure 2 shows the schematic of single stage PA.
Figure 2.Schematic of single stage PA using WIN components
3. SIMULATION AND RESULTS
One tone simulation and two tone simulation is performed. The Rollet factor K>1, makes the
amplifier unconditionally stable. PA circuit with distributed components designed and simulated.
At an input power of 13dBm and output power of 16.8dBm, Power added efficiency of 16.77% is
obtained as in Figure 3.

4
Figure 3.PAE and output power versus input power Figure 4. 1dB compression point
The output power of 14.5dBm at 1dB compression point (P1dB) at an input power of 9dB
obtained as in Figure 5.The two-tone test is performed at frequencies of f1=2.404 GHz and
f2=2.414GHz.The layout is constructed with components from WIN foundry as in Figure 5.
Figure.5. Complete layout of 2.4 GHz PA
4. DESIGN OF FEED FORWARD LINEARIZER
Feed forward linearizer circuit comprises of passive elements and Power amplifier as in shown in
Figure 6. Feed forward system of proper design is proven to provide a better IMD3 suppression1.
The Power dividers with micro strip lines are constructed with MLIN, MCURVE and MTEE. The
MSUB has been chosen to be as H=10.0 mil, Ɛr=9.6 which refer to the layout design. The
Coupled line coupler with 10dB coupling loss is constructed with microstripline MCLIN which is
simulated.

5
Figure 6. Feed forward amplifier circuit
Power amplifier without and with linearization are compared from the simulation results. The
feed forward linearized amplifier resulted with third order intermodulation cancellation of 30dBc
for an output power level of 8.217dBm as in Figure.7.
Figure. 7 Output power comparison of PA with Linearization (marker m7) and without linearization
(marker m8)
The output power of linearized feed forward amplifier improved by 9dBm compared to 15dBm
output power of PA without linearization. There is 6dBm improvement in input power for 1dB
compression point for linearized circuit whereas it is 9dBm for PA without linearization. As
shown in Table.1
Table.1: Comparison of results
Technology Class-E power amplifier @2.4
GHz
Output
power
(dBm)
Input power @1dB
compression
point(dBm)
0.15μm
pHEMT
Before Linearization 15 9
After feed forward
Linearization
24 15

6
5. CONCLUSIONS
A Feed forward linearized power amplifier is designed and presented. The layout is implemented
using 0.15μm WIN GaAs pHEMT Technology. The simulated design resulted with a linear gain
of 8.58dB, The O1dB of 14.59dBm and PAE of 16.77%. Linearization helps to achieve 30dB
improvement in carrier to interference ratio(C/I) and 1dB compression point achieved at an input
power of 15 dBm rather than 6 dBm in PA without Feed forward Linearizer.
REFERENCES
[1] Swapnil parashuram kulkarni, M.R.Madki,Feedforward Linearization Technique to Reduce
Intermodulation Distortion and Spurious Free Dynamic Range(SFDR) Measurements, International
journal of Innovative research and Technology, Vol 3(11), Pp.no: 235 – 239,Nov 2017.
[2] Kevin W. Kobayashi. An 8-W 250-MHz to 3-GHz Decade-Bandwidth Low-Noise GaN MMIC
Feedback Amplifier With +51-dBm OIP3. IEEE Journal of solid-state circuits. oct. 2012, 1(10), pp.
2316-2326
[3] Amanpreet Kaur, Rajbir Kaur. Reducing the Third order Intermodulation distortion by Feed forward
Linearization of Power amplifier. International Journal of Advanced Research in computer and
communication Engineering. 2016, vol (5) pp.294-297
[4] Muhammad Taher Abdullah M.T. Abuelmaatti, Tk.Yeung and G.Parkinson Linearization of GaN
Power Amplifier Using Feed forward and Predistortion Techniques, Proceedings of 3rd IEEE Asia
Symposium on Quality Electronic Design, 2011, pp.282-287
[5] Honarvar M.A, Moghaddasi, Eskandari. Power Amplifier Linearization Using Feed forward
Technique for Wide Band Communication System, Proceedings of IEEE International Symposium on
Radio-Frequency Integration Technology. 2009, pp.72-75
[6] Amandeep Singh Sappal, Manjit Singh Patterh, Sanjay Sharma. Mathematical Modelling of Power
Amplifier with Memory Effects. Indian Journal of Science and Technology.2009, 2(3), pp. 22-23
[7] Katragadda Tejaswi, P. Shanthi Design and Simulation of adaptive feed forward linear power
amplifier for wireless communication, International Journal of Electronics and computer science
Engineering, 2015, 4(1),pp.44-49
[8] Rani Fathima K. A, Raghavendiran T. A. A Novel Intelligent Unified Controller for the Management
of the Unified Power Flow Controller (UPFC) Using a Single Back Propagation Feed forward
Artificial Neural Network. Indian Journal of Science and Technology, 2014 Jan, 7(8), pp.1155-1169
[9] Muthana Kallil Ibrahim. Feed forward Linearization of a Power Amplifier for Wireless
Communication Systems. Journal of Babylon University/Engineering Sciences. 2013, 21(4), pp. 1183-
1193
AUTHORS
She completed her M.Tech in 2006 and submitted her PhD Thesis on Linearization
of MMIC Power amplifiers under Vishvesvarya Technological University,
Belgaum, Karnataka. Her areas of interest are RF circuit Design, MMIC design,
Analog VLSI and antennas. She is currently working as Assistant Professor in the
department of Telecommunication Engineering, R.V.College of Engineering,

7
Bengaluru, Karnataka, India. She has served as the reviewer for IEEE microwave and component letters
and International journal of microwave and wireless technologies.
Dr.Baligar completed his PhD in Electronic Science in 2003 from Bangalore
University, Bengaluru. His field of Interest are VLSI circuits, RF circuits and
Microstrip Antennas. He is currently working as Associate Professor in ECE
dept. at Dr.AIT, Bengaluru, Karnataka, India

DESIGN OF 2.4 GHZ MMIC FEED FORWARD AMPLIFIER FOR WIRELESS APPLICATIONS

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DESIGN OF 2.4 GHZ MMIC FEED FORWARD AMPLIFIER FOR WIRELESS APPLICATIONS