高频小信号调谐放大器

高频小信号调谐放大器 一、实验目的 小信号调谐放大器是高频电子线路中的基本单元电路，主要用于高频小信号或微弱信号的线性放大。在本实验中，通过对谐振回路的调试，对放大器处于谐振时各项技术指标的测试(电压放大倍数，通频带，矩形系数)，进一步掌握高频小信号调谐放大器的工作原理。学会小信号调谐放大器的设计方法。 二、实验原理 图1-1 所示电路为共发射极接法的晶体管高频小信号调谐放大器。它不仅要放大高频信号，而且还要有一定的选频作用，因此晶体管的集电极负载为LC 并联谐振回路。在高频情况下，晶体管本身的极间电容及连接导线的分布参数等会影响放大器输出信号的频率和相位。晶体管的静态工作点由电阻RB1，RB2 及RE 决定，其计算方法与低频单管放大器相同。 图1-1 小信号调谐放大器 晶体管放大器设计 放大器在高频情况下的等效电路如图1-2 所示，晶体管的4 个y 参数yie，yoe，yfe 及yre 分别为 welding procedures of steel pressure vessel NDT 9 JB/T4744-2000 steel pressure vessel products mechanical properties test of welded plate II, mechanical equipment installation engineering 1 GB150-98 2 GB50128-2005 vertical cylindrical steel pressure vessel steel welded specification for construction and acceptance of oil tank 3 JB/ T4735-1997 steel welded atmospheric pressure vessel 4 GB50231-2009 mechanical equipment installation engineering construction and acceptance specification for 5 GB50275-98 compressor, fan and pump installation engineering construction and acceptance specification for lifting 6 HG20201-2000 construction installation engineering construction standard 7, HG ... Pressure gauges, using an installed spark arrestor for acetylene cylinders, illegal carrying, using gas cylinders, each operator fined 20 Yuan. Gas bottle without the hot sun exposure measures, responsibilities of team a fine of 50 Yuan. (7) at height and the opening and provisional protective measures have been taken, the responsible unit fined 200 Yuan, construction person in charge a fine of 50 Yuan. (8) no permit to work and the job in accordance with the provisions, on the job unit fined 300 yuan, the unit will charge a fine of 100 Yuan. 7.5.3 accident penalties (1) injuries fatalities directly punished 1~2 million. Direct responsibility for the accident and have the corresponding responsibility of leadership, such as concerning administrative sanctions, should be 由此可见，晶体管在高频情况下的分布参数除了与静态工作电流IE，电流放大 系数β 有关外，还与工作频率ω 有关。晶体管手册中给出的分布参数一般是 在测试条件一定的情况下测得的。如在f0=30MHz，IE=2mA，UCE=8V 条件下测得 3DG6C的y 参数为: welding procedures of steel pressure vessel NDT 9 JB/T4744-2000 steel pressure vessel products mechanical properties test of welded plate II, mechanical equipment installation engineering 1 GB150-98 2 GB50128-2005 vertical cylindrical steel pressure vessel steel welded specification for construction and acceptance of oil tank 3 JB/ T4735-1997 steel welded atmospheric pressure vessel 4 GB50231-2009 mechanical equipment installation engineering construction and acceptance specification for 5 GB50275-98 compressor, fan and pump installation engineering construction and acceptance specification for lifting 6 HG20201-2000 construction installation engineering construction standard 7, HG ... Pressure gauges, using an installed spark arrestor for acetylene cylinders, illegal carrying, using gas cylinders, each operator fined 20 Yuan. Gas bottle without the hot sun exposure measures, responsibilities of team a fine of 50 Yuan. (7) at height and the opening and provisional protective measures have been taken, the responsible unit fined 200 Yuan, construction person in charge a fine of 50 Yuan. (8) no permit to work and the job in accordance with the provisions, on the job unit fined 300 yuan, the unit will charge a fine of 100 Yuan. 7.5.3 accident penalties (1) injuries fatalities directly punished 1~2 million. Direct responsibility for the accident and have the corresponding responsibility of leadership, such as concerning administrative sanctions, should be 式中，G 为LC 回路本身的损耗电导。谐振时L 和C 的并联回路呈纯阻，其阻值等于1/G，并联谐振电抗为无限大，则jwC 与1/(jwL)的影响可以忽略。 三、调谐放大器的性能指标及测量方法 征高频小信号调谐放大器的主要性能指标有谐振频率f0，谐振电压放大倍数Av0，放大器的通频带BW 及选择性(通常用矩形系数Kr0.1 来表示)等。放大器各项性能指标及测量方法如下: 1、谐振频率 放大器的调谐回路谐振时所对应的频率f0 称为放大器的谐振频率，对于图1-1所示电路(也是以下各项指标所对应电路)，f0 的表达式为 welding procedures of steel pressure vessel NDT 9 JB/T4744-2000 steel pressure vessel products mechanical properties test of welded plate II, mechanical equipment installation engineering 1 GB150-98 2 GB50128-2005 vertical cylindrical steel pressure vessel steel welded specification for construction and acceptance of oil tank 3 JB/ T4735-1997 steel welded atmospheric pressure vessel 4 GB50231-2009 mechanical equipment installation engineering construction and acceptance specification for 5 GB50275-98 compressor, fan and pump installation engineering construction and acceptance specification for lifting 6 HG20201-2000 construction installation engineering construction standard 7, HG ... Pressure gauges, using an installed spark arrestor for acetylene cylinders, illegal carrying, using gas cylinders, each operator fined 20 Yuan. Gas bottle without the hot sun exposure measures, responsibilities of team a fine of 50 Yuan. (7) at height and the opening and provisional protective measures have been taken, the responsible unit fined 200 Yuan, construction person in charge a fine of 50 Yuan. (8) no permit to work and the job in accordance with the provisions, on the job unit fined 300 yuan, the unit will charge a fine of 100 Yuan. 7.5.3 accident penalties (1) injuries fatalities directly punished 1~2 million. Direct responsibility for the accident and have the corresponding responsibility of leadership, such as concerning administrative sanctions, should be 上式说明，当晶体管选定即yfe 确定，且回路总电容CΣ为定值时，谐振电压放大倍数AV0 与通频带BW 的乘积为一常数。这与低频放大器中的增益带宽积为一常数的概念是相同的。 通频带BW 的测量方法:是通过测量放大器的谐振曲线来求通频带。测量方法可以是扫频法，也可以是逐点法。逐点法的测量步骤是:先调谐放大器的谐振回路使其谐振，记下此时的谐振频率f0 及电压放大倍数AV0 然后改变高频信号发生器的频率(保持其输出电压uS 不变)，并测出对应的电压放大倍数AV0。由于回路失谐后电压放大倍数下降，所以放大器的谐振曲线如图1-3所示。 由式(1-14)可得 welding procedures of steel pressure vessel NDT 9 JB/T4744-2000 steel pressure vessel products mechanical properties test of welded plate II, mechanical equipment installation engineering 1 GB150-98 2 GB50128-2005 vertical cylindrical steel pressure vessel steel welded specification for construction and acceptance of oil tank 3 JB/ T4735-1997 steel welded atmospheric pressure vessel 4 GB50231-2009 mechanical equipment installation engineering construction and acceptance specification for 5 GB50275-98 compressor, fan and pump installation engineering construction and acceptance specification for lifting 6 HG20201-2000 construction installation engineering construction standard 7, HG ... Pressure gauges, using an installed spark arrestor for acetylene cylinders, illegal carrying, using gas cylinders, each operator fined 20 Yuan. Gas bottle without the hot sun exposure measures, responsibilities of team a fine of 50 Yuan. (7) at height and the opening and provisional protective measures have been taken, the responsible unit fined 200 Yuan, construction person in charge a fine of 50 Yuan. (8) no permit to work and the job in accordance with the provisions, on the job unit fined 300 yuan, the unit will charge a fine of 100 Yuan. 7.5.3 accident penalties (1) injuries fatalities directly punished 1~2 million. Direct responsibility for the accident and have the corresponding responsibility of leadership, such as concerning administrative sanctions, should be 上式表明，矩形系数Kv0.1 越小，谐振曲线的形状越接近矩形，选择性越好，反之亦然。一般单级调谐放大器的选择性较差(矩形系数Kv0.1 远大于1)，为提高放大器的选择性，通常采用多级单调谐回路的谐振放大器。可以通过测量调谐放大器的谐振曲线来求矩形系数Kv0.1。 四、实验参考电路 1、主要技术指标:谐振频率fo=20.945MHz，谐振电压放大倍数AV0?10-15 dB，通频带BW=1 MHz，矩形系数Kr0.1,10。因fT 比工作频率fo 大(5—10)倍，所以选用3DG6C，选β=50，工作电压为12V，查手册得rbˊb=70, CbˊC=3pF，当IE=1.5mA时Cbˊe 为25pF，取L?2.4μH，变压器初级N2=20 匝，接入系数P1=P2=0.25。 图1-4 单级调谐放大器 2、确定电路为单级调谐放大器，如上图1-4。 3、确定电路参数。 1)设置静态工作点 由于放大器是工作在小信号放大状态，放大器工作电流ICQ 一般选取0.8—2mA为宜，现取IE=1.5mA，uEQ=3V，uCEQ=9V。则 RE = uEQ /IE = 2KΩ 则RA4=2KΩ 取流过RA3 的电流为基极电流的7 倍，则有: welding procedures of steel pressure vessel NDT 9 JB/T4744-2000 steel pressure vessel products mechanical properties test of welded plate II, mechanical equipment installation engineering 1 GB150-98 2 GB50128-2005 vertical cylindrical steel pressure vessel steel welded specification for construction and acceptance of oil tank 3 JB/ T4735-1997 steel welded atmospheric pressure vessel 4 GB50231-2009 mechanical equipment installation engineering construction and acceptance specification for 5 GB50275-98 compressor, fan and pump installation engineering construction and acceptance specification for lifting 6 HG20201-2000 construction installation engineering construction standard 7, HG ... Pressure gauges, using an installed spark arrestor for acetylene cylinders, illegal carrying, using gas cylinders, each operator fined 20 Yuan. Gas bottle without the hot sun exposure measures, responsibilities of team a fine of 50 Yuan. (7) at height and the opening and provisional protective measures have been taken, the responsible unit fined 200 Yuan, construction person in charge a fine of 50 Yuan. (8) no permit to work and the job in accordance with the provisions, on the job unit fined 300 yuan, the unit will charge a fine of 100 Yuan. 7.5.3 accident penalties (1) injuries fatalities directly punished 1~2 million. Direct responsibility for the accident and have the corresponding responsibility of leadership, such as concerning administrative sanctions, should be )确定耦合电容及高频滤波电容 3 高频电路中的耦合电容及滤波电容一般选取体积较小的瓷片电容，现取耦合电容CA2=0.01μF，旁路电容CA4=0.1μF，滤波电容CA5=0.1μF 五、实验内容 参考所附电路原理图G6。先调静态工作点，然后再调谐振回路。 1)按照所附电原理图G6，将JA2 用连接器连好，按下开关KA1，接通12V 电源，此时LEDA1 点亮。 2)调整晶体管的静态工作点: 在不加输入信号(即ui=0)，将测试点TTA1 接地，用万用表直流电压档(20V档)测量电阻RA4 的电压，调整可调电阻WA1，使uEQ=2.25V(IE=1.5mA)，记welding procedures of steel pressure vessel NDT 9 JB/T4744-2000 steel pressure vessel products mechanical properties test of welded plate II, mechanical equipment installation engineering 1 GB150-98 2 GB50128-2005 vertical cylindrical steel pressure vessel steel welded specification for construction and acceptance of oil tank 3 JB/ T4735-1997 steel welded atmospheric pressure vessel 4 GB50231-2009 mechanical equipment installation engineering construction and acceptance specification for 5 GB50275-98 compressor, fan and pump installation engineering construction and acceptance specification for lifting 6 HG20201-2000 construction installation engineering construction standard 7, HG ... Pressure gauges, using an installed spark arrestor for acetylene cylinders, illegal carrying, using gas cylinders, each operator fined 20 Yuan. Gas bottle without the hot sun exposure measures, responsibilities of team a fine of 50 Yuan. (7) at height and the opening and provisional protective measures have been taken, the responsible unit fined 200 Yuan, construction person in charge a fine of 50 Yuan. (8) no permit to work and the job in accordance with the provisions, on the job unit fined 300 yuan, the unit will charge a fine of 100 Yuan. 7.5.3 accident penalties (1) injuries fatalities directly punished 1~2 million. Direct responsibility for the accident and have the corresponding responsibility of leadership, such as concerning administrative sanctions, should be 下此时的uBQ，uCEQ，uEQ 及IEQ 值。 3)调谐放大器的谐振回路使它谐振在20.945MHz 方法是用BT-3 频率特性测试仪的扫频电压输出端和检波探头，分别接电路的信号输入端TTA1 及测试端TTA2，通过调节y 轴，放大器的“增益”旋纽和“输出衰减”旋纽于合适位置，调节中心频率度盘，使荧光屏上显示出放大器的“幅频谐振特性曲线”，根据频标指示用绝缘起子慢慢旋动变压器的磁芯，使中心频率f0=20.945MHz 所对应的幅值最大。 如果没有频率特性测试仪，也可用示波器来观察调谐过程，方法是:在TTA1 处用高频信号发生器注入频率为20.945MHz，大小为25mV 的信号，用示波器探头在TTA2 处测试(在示波器上看到的是正弦波)，调节变压器磁芯使示波器波形最大(即调好后，磁芯不论往上或往下，波形幅度都减小)。 4)测量电压增益AV0 用频率特性测试仪测AV0 在测量前，先要对测试仪的y 轴放大器进行校正，即零分贝校正，调节“输出衰减”和“y 轴增益“旋纽，使屏幕上显示的方框占有一定的高度，记下此时的高度和此时“输出衰减”的读数N1dB，然后接入被测放大器，在保持y 轴增益不变的前提下，改变扫频信号的“输出衰减”旋纽，使谐振曲线清晰可见。记下此时的“输出衰减”的值N2dB，则电压增益为 AV0 =(N2-N1)dB 或者在TTA1 处用高频信号发生器注入频率为20.945MHz，大小为25mV 的信号,使调谐回路处于谐振状态，用高频毫伏表测量RL(RAS) 两端的电压uo, 并利用式(1-13)来计算AV0 若用示波器测，则为输出信号的大小比输入信号的大小之比。如果AV0 较小，可以通过调静态工作点来解决(即IE 增大)。 5) 测量通频带BW 用扫频仪测量BW 先调节“频率偏移”(扫频宽度)旋纽，使相邻两个频标在横轴上占有适当的格数，然后接入被测放大器，调节“输出衰减”和y 轴增益，使谐振特性曲线在纵轴占有一定高度，测出其曲线下降3dB 处两对称点在横轴上占有的宽度，根据内频标就可以近似算出放大器的通频带 BW=B0.7=100kHz ×(宽度) 或者利用描点法来测量。 6) 测量放大器的选择性 放大器选择性的优劣可用放大器谐振曲线的矩形系数Kr0.1 表示。用5)中同样的方法测出B0.1 即可 由于处于高频区，分布参数的影响存在，放大器的各项技术指标满足设计要求后的文件参数值与设计计算值有一定的偏差，所以在调试时要反复仔细调整才能使谐振回路处于谐振状态。在测试要保证接地良好。 六、实验要求 welding procedures of steel pressure vessel NDT 9 JB/T4744-2000 steel pressure vessel products mechanical properties test of welded plate II, mechanical equipment installation engineering 1 GB150-98 2 GB50128-2005 vertical cylindrical steel pressure vessel steel welded specification for construction and acceptance of oil tank 3 JB/ T4735-1997 steel welded atmospheric pressure vessel 4 GB50231-2009 mechanical equipment installation engineering construction and acceptance specification for 5 GB50275-98 compressor, fan and pump installation engineering construction and acceptance specification for lifting 6 HG20201-2000 construction installation engineering construction standard 7, HG ... Pressure gauges, using an installed spark arrestor for acetylene cylinders, illegal carrying, using gas cylinders, each operator fined 20 Yuan. Gas bottle without the hot sun exposure measures, responsibilities of team a fine of 50 Yuan. (7) at height and the opening and provisional protective measures have been taken, the responsible unit fined 200 Yuan, construction person in charge a fine of 50 Yuan. (8) no permit to work and the job in accordance with the provisions, on the job unit fined 300 yuan, the unit will charge a fine of 100 Yuan. 7.5.3 accident penalties (1) injuries fatalities directly punished 1~2 million. Direct responsibility for the accident and have the corresponding responsibility of leadership, such as concerning administrative sanctions, should be 1、整理好实验数据，用方格纸画出幅特性曲线。 2、 思考:引起小信号谐振放大器不稳的原因是什么,如果实验中出现自激现 象，应该怎样消除, 七、实验仪器 1、 BT-3G 型频率特性测试仪一台(选项) 2、 示波器(双踪20MHz)一台 3、 数字万用表一块 4、 调试工具一套 welding procedures of steel pressure vessel NDT 9 JB/T4744-2000 steel pressure vessel products mechanical properties test of welded plate II, mechanical equipment installation engineering 1 GB150-98 2 GB50128-2005 vertical cylindrical steel pressure vessel steel welded specification for construction and acceptance of oil tank 3 JB/ T4735-1997 steel welded atmospheric pressure vessel 4 GB50231-2009 mechanical equipment installation engineering construction and acceptance specification for 5 GB50275-98 compressor, fan and pump installation engineering construction and acceptance specification for lifting 6 HG20201-2000 construction installation engineering construction standard 7, HG ... Pressure gauges, using an installed spark arrestor for acetylene cylinders, illegal carrying, using gas cylinders, each operator fined 20 Yuan. Gas bottle without the hot sun exposure measures, responsibilities of team a fine of 50 Yuan. (7) at height and the opening and provisional protective measures have been taken, the responsible unit fined 200 Yuan, construction person in charge a fine of 50 Yuan. (8) no permit to work and the job in accordance with the provisions, on the job unit fined 300 yuan, the unit will charge a fine of 100 Yuan. 7.5.3 accident penalties (1) injuries fatalities directly punished 1~2 million. Direct responsibility for the accident and have the corresponding responsibility of leadership, such as concerning administrative sanctions, should be