International Journal of Engineering and Techniques - Volume 1 Issue 2, Mar - Apr 2015 RESEARCH ARTICLE
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Design and Modeling of a Ku-Band Power Amplifier using GaNHEMT Technology for Defense and Aerospace Applications Sarat K Kotamraju1, K.Ch.Sri Kavya2, A.Gnandeep Reddy3, G.Naveen Kumar3, K.Nandini Priyanka3, P.V.Santosh3 1
2
Professor, Department of ECE, K L University, Guntur Dt., A.P., India Associate Professor, Department of ECE, K L University, Guntur Dt., A.P., India 3 Students, B.Tech, Department of ECE, K L University, Guntur Dt., A.P., India
Abstract: This paper reports on the design of an ultra wideband power amplifier using 0.25um GaN- HEMT Technology device obtained from the Triquint Semiconductor. There is huge interest in transistors based on Gallium Nitride in recent years due to its high breakdown voltage and its capability to operate in High frequency applications. The load pull analysis is carried out to obtain both the required source and load impedances. The power amplifier with over 10W output power and 42% power added efficiency in the frequency range of 3-5GHz is presented in this paper. The PA is designed using a computer aided design tool called Advanced System Design (ADS).ADS provide two different simulation opportunities. These are referred as schematic simulation and electromagnetic simulation called Momentum. Schematic Simulations are performed on the proposed PA in this paper. Keywords:- GaN-HEMT Technology, Load pull analysis, Advanced system design(ADS)
Introduction: The power Amplifier is one of the key components in a wireless Transmitter system to amplify the low power RF Signal to the required power level at the antenna [1] and the Maximum output power of a transmitter is determined by a power amplifier. To provide the better and sufficient quality of service for high user capacity, one needs a highly linear and highly efficient power Amplifiers. These high efficiency and high output power amplifiers are desirable for defense and aerospace applications. The power amplifiers are generally classified as Trans conductance and switch mode power amplifiers. The Trans conductance power amplifiers operate the transistor as a dependent current source. While the switch mode power amplifiers operates the transistor like a switch.
class power amplifiers the class A power amplifiers\ is the most linear amplifier but its power added efficiency is 50% The switching mode PA’s include class D, class E and class F. They are strongly non linear amplifiers which have a maximum efficiency of 100% Due to the “on” and “off” conditions in the switching mode power amplifiers the voltage and current wave form and do not overlap resulting which power dissipation will be zero and the theoretical efficiency can reach 100% easily [2] In this paper the RF Power GaN-HEMT device model CG40010F manufactured by Cree is used with an operating frequency of 15GHz.The balanced amplifier configuration is used in this paper. GaN-HEMT Technology:
The trans conductance or the biasing class power amplifiers includes class A, class AB, class B and class C where the particular amplifier class is defined by its DC bias condition and the conduction angle analysis. Among the above mentioned biasing
ISSN: 2395-1303
Variety of power amplifiers are available in the market like SiC (Silicon Carbide), GaAs Hetero junction Bipolar Transistors (HBT’s), Si-LDMOS (Lateral diffused MOS), GaAs MESFET’s. Of all the various semiconductor materials and device
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International Journal of Engineering and Techniques - Volume 1 Issue 2, Mar - Apr 2015
technologies the GaN-HEMTs are most promising for defense and aerospace applications due to its high breakdown voltage of nearly 3.2ev and high frequency of operation.[3] and In addition to this GaN devices have some superior properties such as high electron mobility(2DEG) (~1500Cm2/Vs) and high electron density(~1x1013cm-2)[5] When compared to Si and GaAs devices GaN based transistors offer high input and output impedances with high output power density (>10x)[4]. The Comparative analysis of the GaN properties with the other device technologies or materials are summarized as shown in the table 1 below [5]. Characteristic
AlGaAs/
Feature
InGaAs
Electron Mobility
8500
Sic
700
InAlAs/
AlGaN/
InGaAs
GaN
5400
1500-
at
Design of a Proposed Class AB Power Amplifier: Design specifications (Output power, Gain, Efficiency ,PAE)
Active device selection
Stability analysis
Load-pull for determining optimum source and load impedances
2200
300K Critical
0.4
3
0.5
3
Breakdown
Harmonic matching & Biasing network synthesis
field(V/cm) Band gap(Ev)
1.42
3.3
1.35
3.5
Peak electron
1.3
2.0
1.0
1.3
Velocity Final PA characterization
Table 1: Comparative analysis of the Device technologies
Balanced Amplifier Configuration: The Balanced Amplifier Configuration is often used in the Microwave Amplifiers. It was introduced by Eisele, et al. [6] .Generally the Balanced amplifier has two identical single ended Amplifiers (A1, A2) that are connected in parallel by two 3-DB quadrature couplers(900 Hybrid Couplers).These couplers are operated as a power splitter and as a power combiner at the input and the output respectively. Both the input and the output matching of the complete balanced amplifier structure do not depend totally on the Individual amplifying cells as long as both the cells are identical. This unique property of balanced amplifiers has made it more suitable for designing Power Amplifiers [7], Low Noise Amplifiers [8] and the Broadband Amplifiers [9].
ISSN: 2395-1303
Met design specification s No
Yes Efficient and desired amplifier designed
Figure 1: Power Amplifier design flow
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International Journal of Engineering and Techniques - Volume 1 Issue 2, Mar - Apr 2015
Load Pull Investigation: The fundamental source-pull /load-pull simulation is used to find the optimum source and load impedances that can maximize the efficiency of the transistor across the band. The Load pull simulations in this paper are carried out using ADS, HB1 Tone_Load pull design guide with a large signal model of a transistor obtained from Cree. The Load Pull analysis will be performed first and later source Pull analysis will be carried out. The matching networks provide transformation from source and load impedance to the standard 50ohm termination. These values are required to provide desired gain, power added efficiency and the output power. Gain Stage: The first stage of the power amplifier is the Gain stage which is designed to provide most of the RF Gain and to drive the second stage (Power Stage). The different impedance values for input and output matching networks is obtained for different input power levels at the desired frequency In this paper in the output matching network the radial stub is used for achieving wider bandwidths. By the proper design of matching networks using the radial stub the 12Db Gain is achieved only at the gain stage.
The Branch line coupler is used at the power stage which is composed of two parallel arranged identical amplifiers. The reason behind using this approach is to achieve 3Db more power at the output when compared to the single power stage amplifier circuit. This approach is referred as a Balanced Amplifier topology. Here the input power to the power stage is divided by the means of the above 3Db branch line coupler, amplified and then combined by a second coupler. Schematic Simulation Results: The Schematic and the electromagnetic simulations called Momentum can be performed on the designed Power amplifier using ADS. The schematic simulations are performed and presented in this paper. Generally every stage in the power amplifier which includes biasing network, Input and output matching networks at gain stage and a 3DB Branch line coupler at the power stage are designed to produce the desired output power, gain and the efficiency. The simulation performance of the proposed power amplifier is tabulated as follows Frequency
Input
Output
Gain
Gain
Final
Power,
Power,
(Gain
(Power
Gain
Pout
Stage)
Stage)
43dBm
10.34
8.92
Pin
15GHz
24dBm
19.26
Table 2: Schematic Simulation Results
Monte-Carlo Simulation Results: Monte-Carlo method is used to investigate the affects of circuit component tolerances or the manufacturing tolerances in a lumped element or the distributed transmission line components. In this paper 50 iterations were performed with varying input power from 20dBm to 30dBm. The performance of the designed power amplifier is very sensitive to the component tolerances. Where the variations degrade the gain from 19dBm to 13dBm. Which is less than 6dBm when compared to the schematic simulation results. Figure 2: Final Schematic with a Branch Line Coupler
ISSN: 2395-1303
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International Journal of Engineering and Techniques - Volume 1 Issue 2, Mar - Apr 2015
Conclusion: The highly efficient two stage Ku-Band power amplifier has been demonstrated in this paper. A Peak power added efficiency of 40% is obtained at 15GHz frequency. The practical design issues are also discussed with reference to Monte Carlo simulation analysis. The tuning of harmonic components was discarded in this work during the design. By terminating the harmonic components up to second fundamental frequency an increased PAE can be achieved.
[9] chao-Hsiung Tseng and Chih-Lin Chang,” Improvement of return loss bandwidth of balanced amplifier using meta material based quadrature power splitters”, IEEE Microwave and Wireless Component Letters,Vol.18,No.4,April 2008,pp.269271. [10] Ruchi,Sanjay Kumar Tomar, Meena Mishra,Ashok Mittal “ Design and Simulation of a GaN HEMT Based Power Amplifier”,IJECT Vol.5,Issue 4,Oct-Dec 2014.
References: [1]A.Rasmi,A.Marzuki,A.I.AbdRahim,M.R.Yahya, A.F.A.Mat,”A 3.5GHz Medium power Amplifier using 0.15um GaAs PHEMT for WiMAX Applications”, Asia Pacific Microwave Conference, pp.277-280,December 2009. [2]F.H.Rabb, “class:f power amplifiers with maximum flat wavesforms,” IEEE transcations on microwave theory and techniques,vol.45,no.11 nov 1997, pp..2007-2012 [3] Shinichi Hoshi,Hideyuki okita,Yoshiaki Morino,Masanori Itoh,”Gallium Nitride High Electron Mobility Transistor(GaN-HEMT) Technology for High Gain and Highly Efficient Power Amplifiers” Oki Technical Review October 2007/Issue 211 Volume 74,No.3. [4] U.K.Mishra,L.Shen ,T.E.Kazior,Y.F.Wu, “GaN Based RF Power devices and Amplifiers”, IEEE 2008,P .No.287-305. [5] U.Misra, P.Parikh and Y.F.Wu “ AlGaN/GaN HEMTs; An Overview of device operation and applications”, Proceedings of IEEE, Volume 90,pp.1022-1031,June 2002. [6]Eisele,K.M., R.S.Engelbrecht and K.Kurokawa, “ Balanced Transistor amplifier for precise wideband microwave applications”, IEEE Int. Solid state circuit conf., February 1965,pp.18-19. [7] L.Wu, et al, “A Broadband High Efficiency class-AB LDMOS Balanced Power Amplifier “, European Microwave Conference, 2005. [8] Mandeep J.S., Abdullah,H., and Ram N., “ A Compact Balanced low noise amplifier for WIMAX Base station Applications”, Microwave Journal. Vol.53, No.11, Nov.2010, pp. 84-92.
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