低噪声放大器最大限度地提高接收机灵敏度

　　低噪声放大器最大限度地提高接收机灵敏度

　　在每个射频接收系统，如那些在基站，发现手机、GPS、无线局域网接口，和其他应用中，低噪声放大器（LNA）可用于具有较高的内部噪声水平更换放大器提高信噪比。这些系统中的噪声信号来自外部源（外部）和内部电路组件源（内在），表现出设计者可以计算和补偿的特性。外部噪声源可以被过滤，以提供更清洁的信号给放大器，通过精心设计和选择放大器，信号噪声比（SNR）可以最大化。

　　噪声系数（NF）是描述信号链中放大器提供的附加噪声量的设计参数。噪声会降低模拟信号或数字通信系统的比特和帧错误率。在雷达系统中，接收机噪声会限制雷达的有效范围。理想情况下，设计者应该优化总体信噪比，以提供最佳的系统性能。噪声系数定义为噪声因子F，表示分贝［ NF = 10×日志（F）］，与F定义为（Si／Ni）/（/无），比信噪比在输入信噪比在输出。

　　All amplifiers have some amount of thermal noise and other types of noise that they add to the signal they are trying to amplify. And since most RF signals are relatively weak when they reach the receiving antenna， the amplification process should introduce as little noise as possible to deliver the cleanest signal to the rest of the system. In many applications， multiple gain stages are cascaded to greatly improve the signal strength. The Friss equation shows that the noise figure， F1， of the first receiver stage dominates the added noise， and subsequent stages have progressively lower impact on the total noise.