what if the Rout is negative when matching the LNA's output?

[pelican]

sorry to bother, i'm a newbie in this field.

I'm trying to match the output end of a 2.5GHz LNA, but when i calculate the Rout to determine what kind of match structure to use, i find the output R is -0.504-i0.057 ...! the chip i'm using is ATF34143. what should i do then:?:

regards!

 

[Grig]

Re: what if the Rout is negative when matching the LNA's out

Hi

It is impossible to match positive 50Ohm and negative resistance (with out loss of gain). You need modify lna circuit. (Optimize source feedback for ex..)

Regards

 

[gecky]

Re: what if the Rout is negative when matching the LNA's out

sorry to bother, i'm a newbie in this field.

I'm trying to match the output end of a 2.5GHz LNA, but when i calculate the Rout to determine what kind of match structure to use, i find the output R is -0.504-i0.057 ...! the chip i'm using is ATF34143. what should i do then:?:

regards!

With -ve resistant, u'll probably get oscillations at the input. Like what Grig said, add some feedback.

 

[Grig]

Re: what if the Rout is negative when matching the LNA's out

Hi

Another words: You can control output Re(Z) using feedback
make it pos or neg (if you want)

this is true for any amplifier

In our case the neg Re(Zout) may be due to inner device feedback.
So it is possible to compensate this feedback using outer feedback.
Regards