Will the insertion loss behind the LNA affect the sensitivity?

2022-06-02 19:46:56      点击:
Of course, you would say whether the larger the gain of LNA, the better.

The more you can make, is the condition that the loss behind LNA is much smaller than the gain of LNA true?

In theory, that's right.

But in fact, if the gain of LNA is too large.

The rear circuit will be saturated by the LNA output signal.

If the noise floor rises and SNR decreases, the sensitivity will not be good.

Moreover, the larger the gain of LNA, the smaller the IIP3 of its overall receiving path.

Once there are more than two external interference signals, the IMD3 will be larger.

Because IMD3 is very close to RX signal, you can't filter it out by SAW filter.

In this way, IMD3 will increase the noise floor and decrease the SNR of Rx signal.

The sensitivity is still not good.

Poor linearity can also lead to poor sensitivity.

So the gain of LNA is not the bigger the better, nor the smaller the better, but just the best.

At the same time, it is also known that even though LNA can make the loss behind it not affect the sensitivity.

However, if the loss behind it is too large, the sensitivity will still be affected.

That is, the LNA will greatly reduce its sensitivity.