The Study Of Design And Simulation Experiment On L-band Low Noise Amplifier

In modern wireless communications, low noise amplifier(LNA)has a critical influence on the receiver's sensitivity as the first active device in RF front, which theories have been studied for decades. Currently, low-noise amplifier (Low Niose Amplifier, LNA) is widely used in radar, satellite communications, electronic countermeasures, remote telemetry and other electronic systems, as a key component in the receiving system, which has extensive application value and good development prospects. As low-cost and system integration market is accelerated, the goal of low-noise amplifier is lower noise, higher gain, higher linearity, and smaller input and output standing wave ratio, while we seek for small cubage, easy integration and low price.This article designed a low-noise amplifier for wireless communication. Through Agilent ADS software,we completed the entire amplifier circuit design and simulation, the amplifier used Avago's ATF54143 transistor, working band in the 1.8～2.0GHz, the center frequency of 1.9GHz, which also shall be mobile RF LNA circuit operating frequency. The low-noise amplifier in the whole work had a good stability of the band through negative feedback by the source-side manner,after noise matching,the amplifier had a low noise figure which was lower more than 0.6dB; using microstrip line on output port conjugate match, the amplifier had a good power gain which was higher than 17dB, and input and output VSWR are less than 1.5, the basic input and output ports ensured non-reflective.The designed amplifier achieved the desired effect.In this thesis, the following aspects of low noise amplifier principles and design methods were studied, through in-depth analysis, the final design of low-noise amplifier performance indicators were relatively good, consistent with expectations. Microwave low-noise amplifier are active devices, in the early stage of design, we have to learn and grasp the theoretical basis of microwave circuits. In the microwave circuit,there is significantly different from the other circuits because it is characterized by extensive use of passive components, like high frequency resistors,high frequency inductors and capacitors,it is necessary to understand the characteristics of microwave passive components because it will come across some problems and persecutes which aren't in low frequency circuit.The microwave transmission line theory is particularly important,here it focuses on the classification of the transmission line and its equivalent circuit.The microwave network is usually be used to deal with microwave problems,since the use of the network model could reduce the number of passive and active devices;avoid circuit complexity and nonlinear effects;simplify network input and output characteristics; it also be instead of using the basic circuit. One of the most commonly used is the two-port network. The smith chart is used with combination of microwave networks , in the microwave engineering, there are some calculation parameters of the input impedance,load impedance, reflection coefficient and standing wave ratio , in addition to impedance matching problems. If using formula, it will encounter a lot of complex calculations. The smith chart is commonly used in engineering to analyze and calculate, it is convenient and intuitive, and it has a certain accuracy which can meet the design requirements, so the smith chart is used widely as a graphic related issues microwave method. At the end of the second chapter,we simplely analyse the microwave transistor characteristics, including the operating frequency of transistors with different types , noise, gain and suitable circuits, etc., just for selecting right transistor.In the low-noise amplifier design process, its performance is often contradictory, we generally compromise on performance according to the needs and conditions. First, the noise effect plays an important role to the vast majority of radio frequency (RF) and microwave communications, radar and remote sensing system performance, because the noise makes the final decision of the receiver to detecting the smallest signal reliability threshold. We can make achieving minimum noise method after leraning the noise theory of microwave transistor amplifiers and combining with the equal noise figure. To microwave transistors, the gain is another important indicator parameters, as the two-port network, according to port matching conditions, the amplifier power gain can be categorized into power gain, capital gain and use power conversion power gain, these types of gains can be used flexibility as needed. The amplifier needs to guarantee absolute stability on frequency band through stability standard,if not,it will have to take measures to improve,specific methods in Chapter III is explicitly stated. To ensure good two-port amplifier without reflection characteristics, input and output standing wave ratio and dynamic range amplifier should have a good expression in the design. Finally, the third chapter deals with a matching amplifier network structure, including the input matching circuit and output matching circuits, according to different requirements and objectives, the matching form and structure of the circuit are different, this chapter has a detailed exposition.In this thesis,we designed and simulated comprehensively for L-band low noise amplifier through ADS2008 software. After determining the performance of LNA, the first step is to carry out the selection of the transistor device and to design its bias circuit; next we must determine the stability of the amplifier, if the amplifier is unstable in the whole band through the simulation by ADS2008,the microstrip line in series with source feedback could improve stability of the amplifier;followed,the important design parts for low noise amplifier are input and output matching circuits.Input matching network is generally designed to obtain minimum noise matching network for the noise close to the best,not the best power matching network,output matching network adopts conjugate match,which is generally in order improvement of the circuit.Finally,with PCB design for RF circuit features and precautions,we used Altium Designer software to complete the L-band low noise amplifier layout.