2009年全国大学生电子设计竞赛
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本科组】
宽带直流放大器（C
题）
摘 要：本宽带直放大器使用一片ad8039两级前置放大然后经过由VCA810组
成的程控放大电路经过5M和10M的三阶无源滤波器再通过AD811精密运放和BUF634缓冲电路接负载输出，整个系统由单片机通过键盘控制，可以在手动与步进放大倍数之间调节，也可以通过按键调节5M和10M通道的滤波器，该系统性能指标良好，增益可以在0~66.8dB之间调节，在规定的带宽范围内幅度波动没有超过1dB,完成了题目的要求。
关键词： 前置放大 无源滤波 步进放大
Abstract:The broadband amplifier using a straight ad8039 two levels of
preamplifier and then through a programmable amplifier circuit composed of VCA810 through a 5 m and 10 m of third-order passive filter through AD811 precision op-amp and BUF634 load output buffer circuit, the whole system is controlled by a single-chip microcomputer by keyboard, can step between magnification and manual adjustment, can also use buttons adjust the filter of 5 m and 10 m channel, the system performance is good, can be between 0 ~ 66.8 dB gain adjustment, amplitude fluctuations within the bandwidth of the provisions of no more than 1 dB, completed the topic request.
Key Word：pre-amplification Passive filter Step amplification
目录
1. 系统设计 ..................................................................................................................................... 1
1.1设计要求 ............................................................................................................................ 1
1.1.1设计任务 ................................................................................................................. 1 1.1.2技术指标 ................................................................................................................. 1 1.2方案比较与选择 ................................................................................................................ 2
1.2.1可控增益放大方法比较与选择 ............................................................................. 2 1.2.2功率输出部分方法比较与选择 ............................................................................. 2 1.2.3直流稳压电源方案比较 ......................................................................................... 3
2. 单元电路设计及参数计算 .......................................................................................................... 4 2.1前置放大模块 .................................................................................................................... 4 2.2可控增益放大模块 ............................................................................................................ 4 2.3 3dB截止频率为5MHz和10MHz滤波器模块 .................................................................. 5 3. 软件设计 ..................................................................................................................................... 7
3.1程序总体流程图 ................................................................................................................ 7 3.2程序清单（见附录2） ..................................................................................................... 7 4.系统测试....................................................................................................................................... 7
4.1测试仪器 ............................................................................................................................ 7 4.2测试结果 ............................................................................................................................ 8 5. 结束语....................................................................................................................................... 10 参考文献......................................................................................................................................... 10 附录 ................................................................................................................................................ 10
附录1 主要元器件清单 ........................................................................................................ 10 附录2 程序清单 .................................................................................................................... 11