agc高频放大电路的设计[附图 程序].doc

摘 要
随着社会生产力的发展，人们迫切地要求在远距离随时随地迅速而准确地传送信息。于是，无线通信技术得到了迅猛的发展，技术也越来越成熟。而高频放大器是上述通信系统和其它电子系统必不可少的一部分。如在发射设备中，就要用高频功率放大器将信号放大到所需的发射功率；在接收设备中，就要高频小信号放大器将非常微弱的信号放大。由此可知，高频放大器在通信系统中起着非常重要的作用，于是人们对它的要求也越来越高。
该题目的基本要求是：3dB通频带为10kHz～6MHz；基本增益为40dB，可步进调节，步进间隔为6dB；可预置增益值，并显示；最大输出电压≥3V；输入阻抗≥1kΩ；负载电阻为600Ω；单端输入、单端输出。此要求并不难，有多种方案可以实现，如：①采用场效应管作增益控制，高电压输出的集成运放作功率放大，高速ADC对电压进行采样并计算有效值；②采用可编程放大器作增益控制，分立元件实现功率放大，用集成真有效值变换芯片测有效值输出；③利用可编程增益放大器作增益控制，分立元件实现功率放大，用二极管包络检波法进行峰值检波计算有效值等等。
我们选用了第三种方案进行设计。本设计也就是一个宽带放大器，利用可变增益宽带放大器AD603来提高增益和扩大AGC控制范围，通过软件补偿减小增益调节的步进间隔和提高准确度。输入部分采用高速电压反馈运放OPA642作跟随器提高输入阻抗，并且在不影响性能的条件下给输入部分加了保护电路。使用了多种抗干扰措施以减少噪声并抑制高频自激。功率输出部分采用分立元件制作。整个系统通频带为1KHz～20MHz，最小增益0dB，最大增益80dB。增益步进为1dB，60dB以下预置增益与实际增益误差小于1dB。不失真输出电压有效值可达9.5V，输出4.5～5.5V时，AGC控制范围为66dB。
关键词：高频 宽带 放大器 高频放大器 宽带放大器






Design of High Frequency Amplifier Circuit


Abstract：Along with the development of the social productivity, people request urgently at long-distance leave at any time and anywhere and quickly but deliver the information accurately. Hence, the lead-in correspondence technique got the fast development, the technique is more and more maturing .But the high frequency amplifier is an above correspondence system with other electronics system a part of the essential to have. Such as in shot equipments, will use the high frequency amplifier power enlarger enlarge the signal to a blast-off for needing power; In receive equipments, will the small signal in high frequency amplifier enlarger enlarge the very weak signal. As it describes, the high frequency amplifier is very important in correspond system .hence people to it of the request is higher and higher.
This design in fact is a wideband amplifier, making use of wideband amplifier of AD603 which gain can be changed to increase the gain and extend the AGC control scope .Also through software compensate to decrease the gain of changeable step partition with increases accurate degree. Input part adoption high frequency electric voltage feedback carries of OPA642 to follow behind the machine increases importation resistance, and at term that do not affect the function descend added the importation part to protect the electric circuit. Use various methods to reduce yawp and repress the high frequency from arouse. Power output part adoption cell devices to make. The whole wideband covered from 15MHZ to 20MHz, the least gain is 0 dB, biggest gain is 80 dB. The step of gain is 1 dB. The prepare settle gain compares to the actual gain is smaller 0.2dB when under 60 dB. Do not distortion the voltage valid value can amount to 9.5 Vs, when output covers 4.5 to 5.5 V, AGC control scope is 66 dB.
Key words: High frequency Wideband Amplifier High frequency amplifier
Wideband amplifier



目 录
1 前言 .................................................................... 1
1.1 放大器的发展 .......................................................... 1
1.2 放大器的分类 .......................................................... 1
1.3 放大器的主要技术指标 .................................................. 2
1.4 本设计指标要求 ........................................................ 3
2 方案论证与比较 .......................................................... 3
2.1 增益控制部分 .......................................................... 3
2.2 功率输出部分 .......................................................... 5
2.3 测量有效值部分 ........................................................ 5
2.4 自动增益控制 .......................................................... 6
2.5 系统整体框图 .......................................................... 6
3 理论分析与参数计算 ...................................................... 6
3.1 AD603简介 .............................................................6
3.1.1 AD603的主要特点 .....................................................6
3.1.2 AD603的工作原理 .....................................................7
3.1.3 AD603应用要点 .......................................................8
3.2 电压控制增益的原理 .................................................... 8
3.3 AGC的介绍 .............................................................8
3.3.1 AGC的工..