射频宽带放大器的增益控制设计与研究

摘要

The RF broadband amplifier is composed of high bandwidth operational amplifier OPA695 and controllable gain amplifier LMH6502. It can continuously adjust the gain from 0 dB to 60 dB. Since the OPA695 is a current operational amplifier with ultra⁃low voltage⁃input noise,it serves as a preamplifier. LMH6502,as the second⁃stage amplifier,can use DA to control the gain whose variation range is -40~20 dB. The final signal is amplified by the OPA695. As a result,the total gain can reach to more than 60 dB. Zeroing circuit reduces the DC offset of the entire amplifier to the maximum degree,and reduces the noise to the minimum by reducing the power supply ripple and using shielded wire and other methods. Meanwhile,the amplifier’s gain can be pre⁃set,and can be synchronously displayed on LCD.%该系统是基于高频宽带运放OPA695和可控增益放大器LMH6502组合而成的射频宽带放大器，可实现0~60 dB连续可调。由于OPA695是一款具有超低输入噪声电压信号的电流型运放，所以将其作为前级放大。LMH6502作为第二级放大电路可通过DA控制其增益大小，变化范围为-40~20 dB。最后一级经OPA695进行信号的总体放大，使其总增益可达到60 dB以上。调零电路使整个放大器最大程度的减小了直流偏移，并通过减小电源纹波和使用屏蔽线等方法将噪声减小到最小。同时，放大器增益可预设，并可将增益同步显示在LCD上。