L波段接收机的设计毕业设计(论文).doc

毕业设计(论文)L 波段接收机的设计燕山大学毕业设计(论文)任务书学院： 系级教学单位： 学 号030201070007学生 姓名专 业 班 级题 目L 波段接收机的设计课 题来 源实践主 要 内 容对接收机的噪声、动态、增益的性能指标设计 对宽带低噪声放大器、电调衰减器、I The low intermediate frequency plan although may remarkable reduce needs the part number，but the high system gain signs not easy to assign，moreover this kind of structure request has the very high mirror image suppression; But the heterodyne plan may the very good solution mirror image question and the high gain question. After carries on three kind of plans measuring，we use traditional the heterodyne structure to take the channel receiver the plan In order to solve this to be contradictory，we finally have used two under frequency conversion super heterodyne receivers plan. In this kind of structure，the radio-frequency signal that comes inform the antenna after the filter，the low noise amplifier，after the mixing becomes the first intermediate frequency signal，first inspires in this is a fixture. After the intermediate frequency signal passes through once more the filter and the enlargement sends in the second level of mixer，changes the signal to the second intermediate frequency signal，the intermediate frequency amplifier gain also may control，when system work the gain control signal the signal which demodulates by the rear end DSP basis produces. In above group channel，the signal after 2MHz seven steps elliptic function LC filter. LNA carries on the enlargement to the signal，from three level of AGC realization system dynamirange target request，finally enlarges afterwards the signal to in the request level outputs. This group channel does not have frequency conversion processing，because the signaling frequency is lower than 2MHz，may directly carry on to the output signal uses the digitization，then carries on base band processing by DSP. This group channel main guarantee dynamirange，linear，sensitivity target and so on selectivity. 附录 359Front end uses the low noise，the altitude，high increases the field effect tube to take LNA，guarantees the channel the total noise factor and linear the AGC structure with following group channel consistency. 2MHz~30MHz channel uses two-times of frequency conversion super heterodyne structures，the first intermediate frequency for high intermediate frequency 48.8MHz，fronted this kind of structure union six group of Asian frequency multiplication bandpassfilter may obtain the very good mirror image to damp the system to satisfy the system target request. The signal first lowly inserts by2M ~ 30MHz damages the filter to the belt Outside the signal energy carries on the certain suppression，LNA is PUSH - the PULL altitude structure，selects two low noises，high IP3，the high gain field effect tube constitution supplementary structure enhances linear and reduces the entire machine noise，satisfies the system these two targets request. After LNA is a group the reselect which constitutes by six Asian frequency multiplication high selective band pass LC filter，enhances The system selectivity and the antigambling ability，after reduce in the level channel disorderly the level，the reselected six throws the switch by two single tools to carry on the control cut. The sign Aldine mirage from realizes three to four level of AGC，pull even is in front of the frequency conversion the signal power in the identical stable level，after guarantees the frequency conversion linear. First level of AGC is the PIN tube electricity adjusts the attenuators situation AGC，the latter several levels are VGA-AGC. After the double balanced mixer three-frequency conversion enlarges the signal to the request level loses Leaves. The first level of intermediate frequency filter selects the rectangular coefficient to be good，in the belt ripple small table sound wave SAW filter band width 2MHz，the second intermediate frequency for ceramic filter band width 200KHz，the third intermediate frequency is the 10KHz narrow band crystal filter. As for the receiver frequency synthesizer，considered the system request realizes the 1Hzfrequency resolution，at present only has in the inferior frequency band feasible plan uses the DDS - - direct numeral synthesis，with the DDS chip took the frequency synthesizer the core part，passes side and so on frequency multiplication The type realizes the 1Hz frequency resolution. 燕山大学本科生毕业设计(论文)60With 120MHz high pure the steady crystal oscillator took DDS the reference frequency source，first inspires because is on the frequency conversion request frequency is higher，DDS direct output the upper-frequency limit only can arrive the reference frequency 0.4 time，therefore needs to pass through the frequency multiplication，outputs 50.8MHz which first inspires needs ~ 78.8MHz frequency，the length of stride is 10kHz，when scanning took thickly sweeps. Provides second to inspire the frequency another DDS direct output，nearby 38.1MHz Carries on by the 1Hz~10Hz length of stride 。