The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Design >> RF Design >> Max power gain for LNA
https://designers-guide.org/forum/YaBB.pl?num=1075846753

Message started by N Logan on Feb 3^rd, 2004, 2:19pm

Title: Max power gain for LNA
Post by N Logan on Feb 3^rd, 2004, 2:19pm

If I designed an LNA with the input stage being a classical common source type (N-type) and then using a P-type as a unity gain current buffer.

Now I am not quite sure how or what would be wrong, but if the 1st stage had an excellent voltage gain (i.e. biased to have such a low current since current inversely proportional to Av.

And then for the 2nd stage I biased the P-type current buffer with a larger current.

Now why will this not provide the best power gain? Or will it? thanks

Title: Re: Max power gain for LNA
Post by jdeng on Feb 12^th, 2004, 4:22pm

I'm not sure whether you have considered the effect of mismatch between first stage and buffer.

Title: Re: Max power gain for LNA
Post by n.logan on May 8^th, 2004, 1:45pm

Can I put it another way.- If I terminate the output to a large impedence I have a great voltage gain. If I matched it to 50 ohms I don't. How will I buffer the output so that I don't lose gain Av=GmRo

Thanks

Title: Re: Max power gain for LNA
Post by naren on May 20^th, 2004, 3:48am

the 1st stage will see a load cap in the gate of the second stage. you need to cleverly tune out this capacitance int he gate of ur second stage CD buffer. and then match the CD buffer to a 50Ohm.

I am doing same thing here and it works