How to do input and output matching for a Differential LNA?

differential lna

Dear all,

I have a problem that is the method to match a differential LNA same as a normal LNA (i.e. single transistor)? For example, using conjugate matching method and treat the differential LNA as a normal LNA to do the matching? This differential LNA is designed to operate at 2GHz. Thank a lot.

Best rgd.

differential matching

you may do output matching separately: + to gnd, - to gnd.

lna output matching

You have to divide the input impedance of the LNA and then you can synthesize mathing circuit on Smith chart. But the characteristic impedance of the chart must be 25 Ohm instead of 50.

You'll find a L-C combination and you may use this combination by multiplying 2 symmetrically.

But in this case you find differential 50 Ohm!! Not single ended.

After that you must use a Balun circuit to convert Differential-to-Single Ended.

If input impedance of the LNA is real ( I don't think so ) , you may use L-C balun directly..

For instance 50 Ohm single ended to 25 Ohm differential..

If you don't understand that technique , I can upload something..

how to do input and output

Look at the page following:
h*tt*p://w*w*w.analog.com/UploadedFiles/Data_Sheets/4833689284721AD8307_b.pdf

Search at pages 12 & 13 you will see theyr matching tecniques.
You have to scale to 2 GHz.

Hope it will solve your problems.

Mandi

P.S. take away the * from the address. !!!!!!!!!!!!!!!!!!!!!!!!

differential lna matching

Hi All,

I think it is not good to design a lna with differential input. Isn't? The single-differential balun will surely introduce loss and degrade the noise figure. Also, most LNAs, may be all, in the industrial are single-ended input.


Mesfet+

how to do input output

mesfet said:

Hi All,

I think it is not good to design a lna with differential input. Isn't? The single-differential balun will surely introduce loss and degrade the noise figure. Also, most LNAs, may be all, in the industrial are single-ended input.


Mesfet+

Click to expand...

You're right but after LNA??
All components are almost differential such as mixer , IF amplifier , Channel filters etc.
Additional to , Noise behaviour ( not Noise Figure!! ) and IP3 charactersitic of differential LNA is much better than single ended.

Differential structures bring very good "input dynamic" to the system.

The RF input of a mixer generally buffered with transistors therefore input impedance stays constant. In that case conjugate matching should be considered for maximum power transfer.

Similarly , IF output has approximately constant output impedance. Such Mixers have already the buffer transistors , so it's not problem.

The most important thing for a mixer that is to define Operating Point that is specified by manufacturer in such case. Please pay attention for that because all transfer characteristics are depended on that..

Good Luck

mixer output matching single ended

Bigboss,

can you upload your document about the differential matching for LNA? or you can PM me.

differential balun

what is the input and output input is 0 4 8 13 16

and output is blank 2 blank 6 blank CAN YOU HELP ME FIND THE ANWSER BY TONIGHT 9 9 09 CAUSE I GOT TO GO TO SCHOOL TOMMOROW SO PLEASE HAVE IT BY TONIGHT 9 9 09