The Designer's Guide Community
Forum
Welcome, Guest. Please Login or Register. Please follow the Forum guidelines.
Aug 21st, 2019, 6:53am
Pages: 1 2 
Send Topic Print
LNA gain and input matching (Read 17429 times)
yixiusky
Community Member
***
Offline



Posts: 39

LNA gain and input matching
Aug 14th, 2010, 11:23pm
 
Hello everyone

I would like to ask one question

I designed one LNA works frome 1.8 to 2.2 GHz. After meausrement, the input and output matching are ok, but the gain shiift to 1.5GHz. I could not think the reason. Could you help me?

Thank you very much.
Back to top
 
 
View Profile yixiusky   IP Logged
pancho_hideboo
Senior Fellow
******
Offline



Posts: 1424
Real Homeless
Re: LNA gain and input matching
Reply #1 - Aug 15th, 2010, 3:40am
 
yixiusky wrote on Aug 14th, 2010, 11:23pm:
After meausrement, the input and output matching are ok,
but the gain shiift to 1.5GHz.
What do you mean by "the gain" ?
Do you want to mean "a peak of gain or S21"  ?

Show me frequency characteristics of S11, S22 and S21 as LNA.

yixiusky wrote on Aug 14th, 2010, 11:23pm:
I could not think the reason.
I think it is due to characteristics of device intrinsic S21.

Show me frequency characteristics of S11, S22 and S21 of intrinsic device.


Back to top
 
« Last Edit: Aug 15th, 2010, 5:42am by pancho_hideboo »  
View Profile WWW Top+Secret Top+Secret   IP Logged
vp1953
Senior Member
****
Offline



Posts: 172

Re: LNA gain and input matching
Reply #2 - Aug 15th, 2010, 10:44am
 
That seems like a large shift (assuming you are referring to peak gain). How was the measurement done - was the LNA output buffered? If not, what was the load on the LNA output for the gain measurement?
Back to top
 
 
View Profile   IP Logged
yixiusky
Community Member
***
Offline



Posts: 39

Re: LNA gain and input matching
Reply #3 - Aug 30th, 2010, 12:12am
 
Thank you very much for reply, I did more measurement, and i attach the result here.

(1) input matching S11  (both magnitude and smith chart)

(2) Output matching S22  (both magnitude and smith chart)

(3) Gain and NF

My LNA design is 1.8GHz to 2.2GHz, the peak gain should appear at 2 GHz.  

However, the inputmaching peak is around 2GHz, but the output peak is at around 1.5GHz.    

Then the peak Gain is also 1.5GHz.  and the gain decrese around 5dB compare with post layer simulation result.

I do not know the reason why the Peak Gain is shifted to 1.5GHz, and also decreased around 5dB.  Could you please help me? thank you so much
Back to top
 

summary_001.jpg
View Profile yixiusky   IP Logged
yixiusky
Community Member
***
Offline



Posts: 39

Re: LNA gain and input matching
Reply #4 - Aug 30th, 2010, 12:18am
 
I also attach the gain and NF response here.  We can see the peak gain is at 1.6GHz, not 2GHz. My target gain is 15dB, now is 11.9dB.
Back to top
 

C1NF.GIF
View Profile yixiusky   IP Logged
pancho_hideboo
Senior Fellow
******
Offline



Posts: 1424
Real Homeless
Re: LNA gain and input matching
Reply #5 - Aug 30th, 2010, 6:52am
 
yixiusky wrote on Aug 30th, 2010, 12:12am:
However, the inputmaching peak is around 2GHz, but the output peak is at around 1.5GHz.    
Then the peak Gain is also 1.5GHz.  
and the gain decrese around 5dB compare with post layer simulation result.
Show me circuit topology of your LNA especially regarding output load configurations.
Back to top
 
 
View Profile WWW Top+Secret Top+Secret   IP Logged
yixiusky
Community Member
***
Offline



Posts: 39

Re: LNA gain and input matching
Reply #6 - Aug 30th, 2010, 7:58pm
 
I use resistive feedback type LNA ,  I attach the schematic here
Back to top
 

schematic.png
View Profile yixiusky   IP Logged
pancho_hideboo
Senior Fellow
******
Offline



Posts: 1424
Real Homeless
Re: LNA gain and input matching
Reply #7 - Aug 31st, 2010, 6:08am
 
yixiusky wrote on Aug 30th, 2010, 7:58pm:
I use resistive feedback type LNA ,  I attach the schematic here
Simply output matching frequency moves to lower frequency due to parasitic capacitors for Rf, drain of M2 and Lload.
Back to top
 
 
View Profile WWW Top+Secret Top+Secret   IP Logged
RFICDUDE
Community Fellow
*****
Offline



Posts: 323

Re: LNA gain and input matching
Reply #8 - Sep 1st, 2010, 2:49am
 
Your circuit has two resonant circuits that are coupled. The resistive feedback couples the tuned output load and the resonant input matching network, so it is very difficult to simultaneously match the input and have the output tuned for maximum output at the same frequency. It is even more difficult if you are trying to maintain a controlled (matched) impedance at the output too.

Some systems can tolerate some amount of gain variation over frequency, so having the gain at a maximum may not be as important as maintaining a good match and low noise figure.

Alternatively, you could decouple the output and input by removing the shunt feedback, but then the input matching network would have to be redesigned for the impedance change and the gain would be higher (presumably) from input to output. But the increased input/output isolation would decoupled the two tuned networks such that they will not interact (unless there are significant parasitic coupling paths).

Back to top
 
 
View Profile   IP Logged
vp1953
Senior Member
****
Offline



Posts: 172

Re: LNA gain and input matching
Reply #9 - Sep 2nd, 2010, 4:08pm
 
Hi RFICDUDE,

Why in your opinion, did not the measurement data correlate with simulation results? Assuming that there are no bugs with the PDK and the simulations were done correctly, the difference between simulations and actual results seem quite large.
Back to top
 
 
View Profile   IP Logged
yixiusky
Community Member
***
Offline



Posts: 39

Re: LNA gain and input matching
Reply #10 - Oct 2nd, 2010, 1:24am
 
when i measure this LNA, i found one problem.

In this LNA,  the inductor is connected to VDD. So when i meausre the chip, the VDD Pad is easily die.   And then the DC condition is totally wrong.

What should i do to protect the vdd pad?
Back to top
 
 
View Profile yixiusky   IP Logged
yixiusky
Community Member
***
Offline



Posts: 39

Re: LNA gain and input matching
Reply #11 - Oct 2nd, 2010, 8:39pm
 
when i measure this LNA, i found one problem.

In this LNA, there are two VDD pad. One is connect to bias circuit, while another one is connected to LNA core (inductor), as shown in schematic.

When i meausre the chip, among all pads, only the VDD Pad (connected to inductor) is easily dead.  And then there is no DC flow from this VDD pad.

What should i do to protect the vdd pad?
Back to top
 
 
View Profile yixiusky   IP Logged
yixiusky
Community Member
***
Offline



Posts: 39

Re: LNA gain and input matching
Reply #12 - Oct 2nd, 2010, 10:19pm
 
[quote author=pancho_hideboo link=1281853392/0#12 date=1286081414]yixiusky wrote on Oct 2nd, 2010, 8:39pm:

I think gate of M2 are broken actually.
Insert RC filter between Vdd and gate of M2.

Thank you very much.
All pad are ESD PAD
Actually, there is RC filter between Vdd and gate of M2.   i did not draw in the shematic here.  
So i think the gate of M2 has no problem.
Back to top
 
 
View Profile yixiusky   IP Logged
yixiusky
Community Member
***
Offline



Posts: 39

Re: LNA gain and input matching
Reply #13 - Oct 2nd, 2010, 10:36pm
 
Thank you very much

if the ESD diode is broken,  what should I do?  

Yes, i set the current limit for Vdd regulator.

Back to top
 
 
View Profile yixiusky   IP Logged
yixiusky
Community Member
***
Offline



Posts: 39

Re: LNA gain and input matching
Reply #14 - Oct 2nd, 2010, 10:56pm
 
thank you very much  

i will try it right now
Back to top
 
 
View Profile yixiusky   IP Logged
Pages: 1 2 
Send Topic Print
Copyright 2002-2019 Designer’s Guide Consulting, Inc. Designer’s Guide® is a registered trademark of Designer’s Guide Consulting, Inc. All rights reserved. Send comments or questions to editor@designers-guide.org. Consider submitting a paper or model.