How to improve the LNA's IIP3?Thanks!

• Apr 18, 2005

• #1

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dopradar

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lna ip3

Hi All

I am designing a high IIP3 LNA.and meet some difficults to imprive IIP3,what should I do? How many methods can be use to improve the LNA's IP3?
Thanks!

 

• Apr 18, 2005

• #2

khouly

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high ip3 lna

try decrease the gain so u will get better linearity

khouly

 

• Apr 18, 2005

• #3

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toonafishy

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how to improve ip3

Source degeneration feedback can help. But you give up gain.

 

• Apr 19, 2005

• #4

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dopradar

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improve lna ip3

Hi toonafishy.

You mean adding a source inductor to increace the IP3?

Adding a source inductor using microstrip is available or not?

Added after 2 minutes:

Are there some technique to improve IP3 but not give up gain?Thanks!

 

• Apr 19, 2005

• #5

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sunn

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lte lna ip3

dopradar said:

Hi toonafishy.

You mean adding a source inductor to increace the IP3?

Adding a source inductor using microstrip is available or not?

Added after 2 minutes:

Are there some technique to improve IP3 but not give up gain?Thanks!

Click to expand...

increase bias current and voltage cross transistor won't give up gain.

 

• Apr 19, 2005

• #6

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dopradar

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ip3 lna

But improve bias-point also increase the noise figure!

 

• Apr 20, 2005

• #7

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sunn

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improving lna ip3

dopradar said:

But improve bias-point also increase the noise figure!

Click to expand...

Although it could increase your NF but might still ok if your NF is already over 1dB. to prove that you could run system simulation and changing NF said 1.5 or 2.0, unlikely it will drop your senstivity much unless you have no margin, besides increasing bias will also increasing gain which will help senstivity as well.
btw, make sure your test gears are setup up properly, sometimes poor ip3 was not generated by DUT but by test gears.

 

• Apr 21, 2005

• #8

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dopradar

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ip3 in lna

Thank you sunn!

And I have another problem:my LNA's IIP3 is not flat through all frequency band that I need(there is 10dB difference!!!).
So how should I do?

 

• Apr 21, 2005

• #9

dot13

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how to improve gain of a lna

well, i also encount the same problem now.
there are several methods to improve IP3 or linearity:
1. increase bias
2. increase Vgs
3. decrease gain
4. decrease input signal amplitude
5. new schematic topology
.....

it's really a difficult trade-off

 

• Apr 21, 2005

• #10

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elomatic

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improve iip3

Hi,
go thru the answers before. Additionally make sure that your Emitter has a very good ground. About 1mm distance creates an inductivity of about 1nH. That can make the difference of 10dB. Just have a very short distance from ground, that is important.

good luck

 

• Apr 22, 2005

• #11

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sunn

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lna iip3

dopradar said:

Thank you sunn!

And I have another problem:my LNA's IIP3 is not flat through all frequency band that I need(there is 10dB difference!!!).
So how should I do?

Click to expand...

1. make sure LNA is unconditionally stable by:
a. running circuit simulation with pcb layout data addon
b. doing VSWR testing on LNA, suggest 3:1 at least

2. check your bias circuit and Vcc de-coupling circuit working fine, I readed some papers claimed de-coupling circuit caused poor ip3

3. are you design a wide band LNA? did that worest IIP3 happen at lower frequency which normally has higher gain?

 

• Apr 24, 2005

• #12

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myicejade

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how to improve lna noise figure?

if you only improve IIP3 , I think you can increase bias current

 

• Apr 28, 2005

• #13

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dopradar

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improving ip3

Hi sunn.

I met the problem you said(at low frequency IIP3 is poor but gain is higher 2.5dB,10dB IIP3 difference happen)

Hi elomatic.

add a little inductivity at emmiter can increase IIP3,really?