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Problem with LNA and mixer (observing a lot of harmonics)

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brmadhukar

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LNA and mixer problem

Hello,
I have in my IC an LNA and two stage downcovertor along with a VCO+.... . The first mixer is standard Bipolar circuit. I observe a lot of harmonics ( these are components from theee Divisors in PLL ) whenever the LNA matching components are close to the mixer 1 out put pins ( this output is differential). How do I deal with this. Or any reference will be helpful. I cannot re-fab the IC. Other wise there are no problems. In shor there seems to be a problem with LNA and mixer. THe LNA output is clean
TIA
 

Re: LNA and mixer problem

Hi

To degrade hamonic component you should increase linearity. To increase linearity you should increase bias current of Gilbert cell.

Good luck
 

Re: LNA and mixer problem

Try to reduce the PLL bandwidth acting on loop filter components (if it is external). This will filter more out of band spurious while it will make the PLL slower...
If your problem is with in band spurious maybe is another problem.

Bye
Mazz
 

Re: LNA and mixer problem

Hi,
In the same IC I have my IF1 output close to LNA input. In the LNA output I can a significant LO1 output (-55dBm). Is LO leakage a significant problem in Gilbert cell.

I have no problem of phase noise so I think the PLL/VCO nee not be touched.

How can I alter the biasing of the Gilbert cell if we need to increase linearity. I cannot change the IC.

BR
M
 

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