Why PA output doesn't need to match 50 ohms but LNA input ?

[GDF]

Why PA output doesn't need to match 50 ohms but LNA input does?
Considering the BPF or Antenna response, why we need to match?
why we don't?

 

[dingjingfeng]

the impedence is transformed to 50ohm in PA design

 

[vfone]

Re: Why PA output doesn't need to match 50 ohms but LNA inpu

The output impedance of the PA (which usually is very low) SHOULD be matched to 50 ohms to get the maximum power transfer to the load.

LNA’s input doesn’t need to be matched to 50 ohms because the NF match (gamma optimum) usually is slightly different than 50 ohms.

 

[psmon]

There's a matching network at PA output to match its low impedance (to deliver high output power) to 50 ohm (for measurement and also for antenna).

LNA input is matched to 50 ohms for measurement and for antenna.

 

[springf2000]

the isolator of the PA'output is the function to matche the output to 50ohm

 

[Azulykit]

Re: Why PA output doesn't need to match 50 ohms but LNA inpu

My view on this is that there are consequences of not having everything matched, Loss and reflections increase and power transfer is compromised.

Sometimes the effort to match everything is worse than the consequences of not being matched. In this case "Matching is not necessary".

It depends upon the situation.

 

[springf2000]

to PA,best gain match not mean best linearity,best linearity match not mean best gain and power match,in common, the S11 and S22 is about -10, it is not the same as the small signal amplifier!
doont forget push the help button to add points to me!
thanks

 

[eladg]

Re: Why PA output doesn't need to match 50 ohms but LNA inpu

u dont need to match PA b.c. at high power S22 is not good, there is difrent between small signal and large signal.
at PA u should match it for max out power tpo load.

u should match the output s22 of lna.
at the enter point of lna u dont have (u must not) to match it for 50 ohm , u should match it for noise (if the ripple dont care for u). at this case u will not get the maximum gain of the lna, but the noise figure of the system will be goo.
the only reson to match input of lna to 50 ohm (or near) is the ripple - not power not transfer power (enery) non of them - just ripple !!!!!!!!!!

 

[ning0703]

got it and know much about the PA knowledge, i give my point on pa match , maybe we know the loadingpull , you need to select the output impedence for MAXpower of max efficiency , there are not the same point , so deside which you want and then select the impedence point