California State University, Northridge
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CALIFORNIA STATE UNIVERSITY, NORTHRIDGE Design of a 5.8 GHz Two-Stage Low Noise Amplifier A graduate project submitted in partial fulfillment of the requirements For the degree of Master of Science in Electrical Engineering By Yashika Parwath August 2020 The graduate project of Yashika Parwath is approved: Dr. John Valdovinos Date Dr. Jack Ou Date Dr. Brad Jackson, Chair Date California State University, Northridge ii Acknowledgement I would like to express my sincere gratitude to Dr. Brad Jackson for his unwavering support and mentorship that aided me to finish my master’s project. With his deep understanding of the subject and valuable inputs this design project has been quite a learning wheel expanding my knowledge horizons. I would also like to thank Dr. John Valdovinos and Dr. Jack Ou for being the esteemed members of the committee. iii Table of Contents Signature page ii Acknowledgement iii List of Figures v List of Tables vii Abstract viii Chapter 1: Introduction 1 1.1 Communication System 1 1.2 Low Noise Amplifier 2 1.3 Design Goals 2 Chapter 2: LNA Theory and Background 4 2.1 Introduction 4 2.2 Terminology 4 2.3 Design Procedure 10 Chapter 3: LNA Design Procedure 12 3.1 Transistor 12 3.2 S-Parameters 12 3.3 Stability 13 3.4 Noise and Noise Figure 16 3.5 Cascaded Noise Figure 16 3.6 Noise Circles 17 3.7 Unilateral Figure of Merit 18 3.8 Gain 20 Chapter 4: Source and Load Reflection Coefficient 23 4.1 Reflection Coefficient 23 4.2 Source Reflection Coefficient 24 4.3 Load Reflection Coefficient 26 Chapter 5: Impedance Matching 28 5.1 Need for Impedance Matching 28 5.2 L-Section Matching Network 29 5.3 Single Stub 37 Chapter 6: Design Simulation on ADS 42 6.1 DC Biasing 48 6.2 Final Schematic 49 Chapter 7: Layout and EM Simulations 53 7.1 Layout 53 Chapter 8: Conclusion 58 References 59 iv List of Figures Figure 1.1: Block diagram of a communication System 1 Figure 1.2: Signal representation of amplification process 2 Figure 2.1: Different system impedance performance 5 Figure 2.2: Signal to noise ratio 7 Figure 2.3: Linearity and dynamic range 7 Figure 2.4: Two-port network 8 Figure 2.5: S-parameters of a two-port network 8 Figure 2.6: Design flow chart 11 Figure 3.1: Schematic for plotting S-parameters 1 2 Figure 3.2: Magnitude and phase of the S-parameters for the BFU725F transistor 1 3 Figure 3.3: Schematic of transistor for stability check 15 Figure 3.4: Transistor stability K-factor output 15 Figure 3.5: Δ of the transistor 15 Figure 3.6: General transistor amplifier circuit with source and load gains 20 Figure 4.1: Reflection coefficient of a transmission Line 2 3 Figure 4.2: Gain circle of 16 dB intersecting noise circle of 1.3 dB 24 Figure 4.3: Gain circle of 16.5 dB 25 Figure 4.4: Gain circle of 17.12 dB 25 Figure 4.5: Gain circle of 17.3 dB 25 Figure 5.1: Block diagram of LNA with matching networks 28 Figure 5.2: 1+jx circle on the Smith chart 29 Figure 5.3: L-section matching for zL inside 1+jx circle 30 Figure 5.4: L-section matching for zL outside 1+jx circle 30 Figure 5.5: L-section source impedance matching on the Smith chart 33 Figure 5.6: L-section source matching network 34 Figure 5.7: L-section load impedance matching on the Smith chart 36 Figure 5.8: L-section load matching network 37 Figure 5.9: Single stub source impedance matching on the Smith chart 38 Figure 5.10: Single stub source matching network 39 Figure 5.11: Single stub load impedance matching on the Smith chart 40 Figure 5.12: Single stub load matching network 41 Figure 6.1: L-section source and load matching networks 42 Figure 6.2: Output of the L-section matching networks 42 Figure 6.3: Schematic of single stub source and load matching network 43 Figure 6.4: Output of matching networks using single stub matching 44 Figure 6.5: LineCalc tool in Ads for MLIN 45 Figure 6.6: Single stage LNA using MLIN 46 Figure 6.7: Output of single stage LNA using MLIN 46 Figure 6.8: Two-stage LNA with MLIN 47 Figure 6.9: Output of the two-stage LNA 47 Figure 6.10: DC biasing network 48 Figure 6.11: Two-stage LNA with DC biasing circuit 49 Figure 6.12: MAPER in ADS 50 Figure 6.13: Final schematic of the two-stage cascaded low noise amplifier 51 v Figure 6.14: Output of two-stage cascaded low noise amplifier 52 Figure 7.1: Final layout of the two-stage 53 Figure 7.2: Substrate properties for EM simulations 54 Figure 7.3: 3D view of the layout 54 Figure 7.4: Schematic with EM symbol for cosimulation 55 Figure 7.5: EM cosimulation output 56 Figure 7.6: Final layout for fabrication 56 Figure 7.7: PCB of the two-stage LNA 57 vi List of Tables Table 1.1: Overall design specifications 3 Table 3.1: Transistor S-parameter values at 5.8 GHz 12 Table 6.1: Parameters of the microstrip substrate 45 vii Abstract Design of a 5.8 GHz Two-Stage Low Noise Amplifier By Yashika Parwath Master of Science in Electrical Engineering Efficient communication systems are essential in the modern-day world. There are various blocks that constitute a communication system. This project emphasizes one such block: the low noise amplifier (LNA). LNAs are used in the receiver to amplify weak signals while contributing the least noise possible to the system. These attributes of high gain and low noise figure of an LNA are called for in any receiver block. A low noise amplifier operating in the microwave frequency range will find applications in satellite radio, cellular devices, radar, and microwave communication systems. The objective of this project is to design a low noise amplifier operating at 5.8 GHz with a target gain of greater than or equal to 30 dB and a noise figure of less than 2 dB from a cascaded two-stage design using two NXP BFU725F transistors. To ensure the design’s empirical performance is on par, it is supported with the respective theory and analytical calculations. The software simulations are done using Keysight ADS software while a graphical tool, the Smith chart, is used for the transmission line design. A layout of the final schematic is generated and an electromagnetic (EM) simulation of it is run to verify the performance at the layout level. The final design met the project goal with a gain of 30.06 dB and a noise figure of 1.36 dB at 5.8 GHz. The final design was fabricated and was ready for testing in the lab, but this could not be done due to COVID-19. viii Chapter 1: Introduction Modern wireless communication systems operate using high frequency signals. Signals operating at high frequency have greater bandwidth, higher data rate, and reduced antenna size. These advantages only follow if the system is designed to operate at these high frequencies called as radio frequencies (RF). RF ranges from 3 KHz to 3 GHz sometimes amalgamated with microwave frequencies that range from 1 GHz up to 300 GHz. Because of this, communication and high frequency signals are interdependent. 1.1 Communication System Communication is defined as the means of propagating information from one point to another point. A simple RF communication block is seen in Figure 1.1. In the transmitter, a low frequency modulated signal is upconverted to high frequency signal by mixing it with a local oscillator signal then it is amplified by a power amplifier to facilitate long distance transmission. As mixer in up conversion generates multiple frequencies, and a transmitter filter is used before sending the message carrying signal out into free space via an antenna. Figure 1.1: Block diagram of a communication system. In the receiver, the weak signals received are filtered first to discard the undesired frequencies, followed by amplification through a low noise amplifier then down conversion to a low frequency baseband signal using a mixer and a local oscillator to retrieve the original transmitted signal. 1 While this briefly outlines the concept of communication, this project focuses on the definition, theory, and design of a low noise amplifier which finds its application specifically in the receiver side of a communication system. 1.2 Low Noise Amplifier A low noise amplifier is a critical block used to increase the strength of the weak received signals while adding the least noise possible to the system. Figure 1.2 shows the process of amplification. The gain resulting from amplification and noise figure are crucial parameters to establish the performance of an LNA. A major difference between power amplifiers and LNAs is the noise each contribute to the system. LNAs have significantly lower noise figure as compared to power amplifiers. There are numerous applications that require amplification of signals with minimum noise such as satellite communications, RADAR, smart phones, Wi-Fi, GPS (global positioning system), etc. Based on the frequency of operation, LNAs find their application in the above. For example, an LNA operating at 900 MHz is used in cellular communication where as an LNA operating at 12 GHz finds its application in high frequency RADAR. Figure 1.2: Signal representation of amplification process.