低噪声放大器优秀毕业论文

从天线接收的微弱信号由处于射频接收机前端的放大器进行放大，因此要求该放大器具有一定的增益和较小的噪声系数。 本文借助Agilent公司的射频电路设计软件ADS(Advanced Design System)进行辅助设计一款高增益低噪声放大器(LNA)，并对其进行了仿真验证。1 射频放大器的组成 单级射频放大器的组成如图1所示，包括射频晶体管放大电路和输入、输出匹配网络三部分。2 射频放大器的设计2．1 晶体管的选择 选择好晶体管器件对低噪声放大器的设计至关重要。 根据工作频率、增益和噪声系数等指标要求，同时考虑到设计、仿真时便于得到相应的元器件模型，最终选用Avago公司的高电子迁移率晶体管(E-PHEMT)ATF-58143来进行设计(可以在Avago公司的网站上下载到ATF-58143的元件模型)。2．2 偏置电路的设计 设计LNA首先需要确定静态工作点，利用ADS中的“DC_FET_T”的模板可以很方便地仿真出其输出特性曲线。再参考ATF-58143的datash eet，可以确定当Vds=3 V，Ids=35 mA时，各项设计指标满足要求。 确定静态工作点后，就要确定偏置电路的形式和参数。不需人工计算，借助ADS中的设计向导工具(DesignGuide→Amplifier→Tools→ Transistor Bias Utility)可以轻易完成。因为ADS所提供的元件数值是非标称的，所以需要设计者用与ADS提供的数值接近的标称元件进行替代。偏置电路及各点静态参数如图2所示。2．3 稳定性分析及改善 晶体管绝对稳定的条件是K>1，|△|<1。其中： 如果这两个条件不能同时得到满足，电路将存在潜在的不稳定和振荡的可能。对上述偏置条件下的晶体管进行稳定性仿真分析发现，在要求的工作频段内其稳定系数K<1，不满足绝对稳定的条件。 通过引入负反馈的方式可以改善电路的稳定性，同时也能够拓展工作带宽。在输出端和输入端之间串联RC电路引入负反馈，其中的R需要满足条件： 同时在两个源极加上小的电感引入负反馈进一步改善稳定性，该电感的值需反复调节后方能确定。 对引入负反馈后的电路再次仿真，其工作频带内稳定系数K>1，满足绝对稳定条件。2．4 最小噪声系数的输入匹配电路设计，最大增益的输出匹配电路设计 如果输入匹配电路和输出匹配电路使射频器件的输入阻抗Zin和输出阻抗Zout都转换到标准系统阻抗Zo，即Zin=Zo，Zout=Zo(或，如图1所示)就可使器件的传输增益最高。但输入、输出匹配时，噪声并非最佳。当ΓS=Γopt时，可以得最小的噪声系数。 利用ADS可以很方便地绘制出等功率增益圆和等噪声系数圆，如图3所示。从图中可以看出，如果从m2点匹配到标准系统阻抗，将可以使电路获得最大的增益；如果从m3点匹配到标准系统阻抗，将可获得最小的噪声系数。显然最大增益和最小噪声系数不可同时得到。对于低噪声放大器，首要的是考虑最小噪声系数，因此对m3点进行匹配。借用ADS的自带工具“Smith Chart Utility Tool”进行，只要在其中设置好频率、源阻抗和目标阻抗值，就可以设计出所需要的输入匹配电路。 在输入端匹配完成以后，在原理图中加入阻抗测量控件测出输出阻抗，再次使用“Smith Chart Utility Tool”将输出阻抗匹配到标准系统阻抗，就可得到最大增益的输出匹配电路。 当输出端的匹配完成后，因为改变了从输入端向里看的等效阻抗Zin，输入端的回波损耗会变差。为此，可以采用优化控件对输入端和输出端的匹配电路进行同时的优化改进，也可以使用Tunig工具进行调节。2．5 最终电路及仿真结果分析 匹配及优化后的电路如图4所示，电路中各元件的作用分别是：C6、L6是输入匹配电路；C7、L7是输出匹配电路；L1、L5、C3、R5是反馈元件；L3、L4是扼流电感；C4、C5是隔直耦合电容；C1、C2是旁路电容。 需要说明的是，反馈电感L1、L5和匹配电路中的元件C6、L6、C7、L7等因为数值较小，在工程中常用微带线来代替。 仿真结果如图5所示。其工作带宽达500 MHz，中心频率处增益接近20 dB，输入输出反射损耗小于-10 dB，噪声系数小于0．5 dB，稳定系数大于1。如果断开反馈电路后再次仿真，会发现增益有所加大，但稳定系数将小于1，放大电路将不能正常工作。3 结论 通过射频低噪声放大器的设计与仿真，可以看到使用ADS辅助设计电路，理论计算简单，设计过程快速，参数修改容易，验证方便，缩短了设计周期，提高了设计精度，在工程中具有实用价值。By a weak signal from the antenna in the rf receiver front-end amplifier amplification, therefore asked the amplifier gain and low noise factor.In this paper, with the aid of Agilent ADS of rf circuit Design software (Advanced Design System) for aided Design a high gain and low noise amplifier (LNA), and the simulation verification.1 the composition of the rf amplifierSingle stage composed of rf amplifier is shown in figure 1, including rf transistor amplifier circuit and the input and output matching network of three parts.2 the design of the rf amplifier2.1 the choice of the transistorGood selection transistor components for the design of the low noise amplifier is very important.According to the working frequency, gain and noise figure index requirements, at the same time when considering the design, the simulation is easy to get the corresponding components model, finally choose Avago company of high electron mobility transistor (PHEMT) E ATF - 58143 for design (can be downloaded on Avago company web site to the ATF components model - 58143).2.2 the design of the bias circuitDesigning LNA first need to determine the static working point, the use of ADS "DC_FET_T" templates can be easily in the simulation of the output characteristic curve. Reference ATF - 58143 again datash eet, can be determined when the Vds = 3 V, Ids = 35 mA, the design indexes meet the requirements.After determine the static working point, shall determine the form and the parameters of bias circuit. Do not need artificial calculation, with the aid of ADS in the design wizard tool (DesignGuide - Amplifier - > Tools - Transistor Bias, the Utility) can be done easily. Because the ADS provided by the component values are nominal, so designers need to use with the ADS provide alternative values close to the nominal elements. Bias circuit and some static parameters as shown in figure 2.2.3 stability analysis and improvementTransistor is K > 1, the absolute and stability of the | delta | < 1. Among them:If the two conditions cannot be satisfied at the same time, there will be potential instability and oscillatory circuit. Transistor of the bias conditions stability simulation analysis found that the stability coefficient within the required working frequency band K < 1, can not meet the needs of absolute stability conditions.By introducing feedback on ways to improve the stability of the circuit, but also can extend working bandwidth. Between the output and the input series RC circuit is introduced into feedback, of which R need to meet the conditions:In both the source and small inductance is introduced into feedback to further improve the stability, the value of the inductance to repeatedly adjust the rear can be determined.Introduction of negative feedback circuit simulation again, within its working frequency stability factor K > 1, meet the absolute stability condition.2.4 minimum noise factor input matching circuit is designed, the biggest gain of the output matching circuit designIf the input matching circuit and the output matching circuit of rf devices Zin the input impedance and output impedance Zout impedance Zo are transformed to the standard system, namely the Zin = Zo, Zout = Zo (or, as shown in figure 1) to make a device transport the highest gain. But when input and output matching, noise is not the best. When Γ S = Γ opt, could get the minimum noise figure.ADS can be easily draw power gain and noise coefficient, as shown in figure 3. Can be seen from the diagram, if from m2 point impedance matching to the standard system, will be able to make the circuit gain maximum gain; If impedance matching to the standard system, from the m3 point will be minimal noise coefficient can be obtained. Obviously the biggest gain and the minimum noise figure cannot get at the same time. For low noise amplifier, the first is to consider the minimum noise figure, and so on m3 point matching. Use ADS bring tools "Smith Chart the Utility Tool", in which as long as the set frequency, source impedance and the target impedance value, can the input matching circuit design need.In the input matching is complete, add impedance measurement control measure in principle diagram output impedance, again using "Smith Chart the Utility Tool will impedance, output impedance matching to the standard system can get the maximum gain of the output matching circuit.When the output matching is completed, because has changed from the input to see the equivalent impedance Zin, will get poor return loss at the input. For this purpose, the optimal control can be used for the input and the output matching circuit optimization to improve at the same time, also can use Tunig tools.2.5 the final circuit analysis and simulation resultsMatched and optimized circuit as shown in figure 4, the role of each element in the circuit are respectively: C6, L6 is input matching circuit; C7, is about the output matching circuit; L1, L5, C3, R5 is feedback element; L3, L4 is choke inductance; C4, C5 is the direct coupling capacitance; C1, C2 is the bypass capacitor.Feedback to be sure, inductance L1, L5 and matching circuit element in C6, L6, C7, about because small amounts, such as microstrip line to replace the commonly used in engineering.The simulation results as shown in figure 5. Its working bandwidth of 500 MHz, the center frequency close to 20 dB gain, input and output return loss is less than 10 dB of noise coefficient is less than 0.5 dB, stability factor greater than 1. If disconnect again after feedback circuit simulation, will find the gain increased, but the stability coefficient will be less than 1, the amplifying circuit will not work properly.3 conclusionThrough radio frequency low noise amplifier design and simulation, can see use ADS auxiliary circuit design, the theoretical calculation is simple, rapid design process, parameter modification easy, convenient, shorten the design cycle,请采纳。

高效率音频功率放大器的研制白林景,邵光存,李岸然,常兴连,王振伟(山东省科学院激光研究所,山东济宁 272100) 摘 要:本设计以高效率D类功率放大器为中心,输出开关管采用高速场效应管,连接成互补对称H桥式结构,兼有输出1: 1双变单电路和输出短路保护功能,比较理想地实现了输出功率大于2w,平均效率可达到75%的高效音功率放大器。关键词:D类音频功率放大器; PWM调制器; H桥功率放大器中图分类号: TN722. 1 文献标识码:A引言全球音频领域数字化的浪潮以及人们对音频节能环保的要求,要求我们尽快研究开发高效、节能、数字化的音频功率放大器。传统的音频功率放大器工作于线性放大区,功率耗散较大,虽然采用推挽输出,仍然很难满足大功率输出;而且需要设计复杂的补偿电路和过流,过压,过热等保护电路。D类开关音频功率放大器的工作于PWM模式,将音频信号与采样频率比较,经过自然采样,得到脉冲宽度与音频信号幅度成正比例变化的PWM波,经过驱动电路,加到MOS的栅极,控制功率器件的开关,实现放大,放大的PWM信号送入滤波器,还原为音频信号。从而实现大功率高效率的音频功率放大器。系统电路本文采用H型桥式D类功率放大电路,电路如图一所示。图一 音频功率放大器电路(1) 三角波产生电路利用NE555构成的多谐振荡器以恒流源的方式对电容线性冲、放电产生三角波。接通电源瞬间,NE555芯片的3脚输出高电平,二极管D2、D3 截止,D1、D4 导通, Vcc通过T1 , T2 , R1 ,D1 对电容C1 恒流充电,当C1 上电压达到2 /3Vcc时,NE555芯片的输出发生翻转,即3脚输出低电平,此时,D2、D3 导通, D1、D4 截止,电容C1 通过D2 , T3 ,T4 , R2 恒流放电,直到C1电压等于1 /3Vcc,电容又开始充电,如此循环,电容C1上可以得到线性度良好的三角波。为了提高带负载能力,输出通过由LM358A组成的电压跟随器。输出三角波频率的计算:电阻R1 上电压等于T1 的VVbe≈ 0. 7V,故流过R1 的电流I = 0. 7V /300Ω = 2. 33mA,忽略T1 的基极电流,则流过R1 的电流即为T2 的射级电流,约等于T2 的集电极电流,故C1 的充电电流约为2mA,同理, C1 的放电电流约为2mA。设充电时间为t1 ,放电时间为t2 ,则有:23Vcc =13Vcc +i ×t1C13Vcc =23Vcc -i ×t2C可得三角波的周期: T = t1 + t2 =2Vcc ×C3 ×i故三角波频率为: f =3 ×i2Vcc ×C(2)前置放大电路 前置放大电路采用低噪声、高速运放的NE5532运算放大器,组成增益可调的同相宽带放大电路。功放最大不失真输出时,负载上等效正弦波的电压峰峰值为VP - P ,载波调制的调制波(正弦波)最大峰峰— 27 —值为VP - Pm ax ,对应的调制放大增益为AV2 =VP - PVP - Pm ax,运算放大电路中反馈电阻为R8 ,反相端电阻R7 ,则前置放大器的增益AV1为:AV1 = 1 +R8R7,通过选取调制波的峰值电压VP - Pm ax和调整R8 的阻值,可实现整个功率放大单元的电压增益连续可调。(3)脉宽调制( PWM)电路 采用高速、精密的比较器芯片,以音频信号为调制波,频率为f的三角波为载波,两路信号均加上1 /2Vcc的直流偏置电压,通过比较器进行比较,得到幅值相同,占空比随音频幅度变化的脉冲信号。(4)驱动电路 驱动电路由施密特触发器芯片和三极管组成,两个三极管组成的互补对称式射极跟随器。PWM信号经过驱动电路后,形成两个前后沿更加陡峭的倒相脉冲,两脉冲之间有一定的死区时间,防止了桥式驱动电路出现直通现象。(5) H型桥式驱动电路 由场效应管组成的功率开关管和四阶巴特沃兹LC滤波电路组成。T9、T12导通, T10、T11截止时,负载上的电压降VM AB0 =Vcc; T10、T11导通,T9、T12截止时,负载上的电压降VAB = - Vcc,因此,负载上的电压降可达到2倍的电源电压。解调信号放大后经过LC滤波送到扬声器。(6)短路保护电路 短路(或过流)保护电路采用0. 1过流取样电阻与扬声器串联方式, 0. 1电阻上的取样电压经过由NE5532组成的减法放大器进行放大。电压放大倍数为:Av =R19R17经放大后的音频信号再通过由D9、C9、R20组成的峰值检波电路,检出幅度电平,送给电压比较器U7的“ + ”端,U7的“—”端电平设置为5. 1v,由R22和稳压管D12组成,比较器接成迟滞比较方式,一旦过载,即可锁定状态。正常工作时,通过0. 1上的最大电流幅度Im =Vcc /(R + 0. 1) , 0. 1上的最大压降为0. 1 ×Im ,经放大后输出的电压幅值为Vim ×AV = 0. 1 ×Im ×AV ,检波后的直流电压稍小于此值,此时比较器输出低电平, T13截止,继电器J1不吸合,处于常闭状态,电源Vcc通过常闭触点送给功放。一旦扬声器两端短路或输入电流过大, 0. 1上电流、电压增大,经过电压放大、峰值检波后,大于比较器反相端电压,则比较器翻转为高电平并自锁, T13导通,继电器吸合,切断功放Vcc电源,功放电路得到保护。R21、C11、D10、D11组成开机延时电路,防止开机瞬间比较器自锁,关机后C11上的电压通过D10快速放掉,以保证再开机时C11的起始电压为零。讨论D类放大器工作于开关状态,无信号输入时无电流,而导通时,没有直流损耗。事实上由于关断时器件尚有微小漏电流,而导通时器件并没有完全短路,尚有一定的管压降,故存在较少直流损耗,实际效率在80% - 90% ,是实用放大器中效率最高的。参考文献:[ 1 ]Wing - Hong, Lau , IEEE Trans. Realization ofDigitalAudi2o Amp lifier Using Zero - Voltage - Switched PWM PowerConverter, Circuits Syst . Vol 47,NO. 3,March 2000.[ 2 ]Ashok Bindra. All - digital App roach HikesAudio Quality InConsumer Product.[ 3 ]李子升,吴锦铭,钟国新. 高效率音频功率放大器.[ 4 ]李振玉,姚光圻. 高效率放大及功率合成技术. 中国铁道出版社, 1985.[ 5 ]陈伟鑫. 新型实用电路精选指南. 电子工业出版社.[ 6 ]瞿安连. 应用电子技术. 北京科学出版社, 2003.[ 7 ]王金明等编著. 数字系统设计. 电子工业出版社出版.[ 8 ]全国大学生电子设计竞赛获奖作品精选. 1994 - 1999.[ 9 ]虎永存,现代音响技术, D类放大器的原理和电路, 1998年第5期.[ 10 ]无线电2004合订本第2、3期. 无线电杂志社,人民邮电出版社.这个是从付费论文网站上买的，真珍贵的