Learning Forum

[prajput]

Why do we use low noise amplifier at the front end in the receiver chain?

[Charlotte Blair]

 The signal present at the antenna of the receiver consists of a mixture of the desired signal with noise. In addition to that, the signal level will be very low because of the attenuation caused by the medium resulting in low signal to noise ratio (SNR). This signal level will not be sufficient enough to be decoded by the other components of the receiver. In addition, using a low noise amplifier (LNA) as the receiver front end will decrease the overall noise figure. 

[rtk]

What is noise figure and why it should be low for a receiver?

[Charlotte Blair]

 The noise figure of a system is the measure of degradation to the signal to noise ratio of the input signal that will cause because of its internal components. So, it is preferred to have a low noise figure for your receiver design. Also, a receiver uses a Low Noise Amplifier (LNA) for better performance.

[prajput]

How does the LNA reduce the noise figure of the receiver?

[Charlotte Blair]

Hi -

At the input of the receiver the signal can be very close to the noise floor of the receiver system. In order to boost the incoming signal, a low noise amplifier (LNA) is required. The LNA will boost the signal level of the signal hence increasing the SNR which will help reduce any errors in signal detection hence increasing the overall performance of the system.