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How to design a high input impedance LNA?

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tony_lth

tony_lth

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HI, ALL,
I want to design a high input impedance LNA, i.e. input 2K about, and the output impedance is 50R.
The freq band is from 100M to 600M,
How to design it?
Many thanks.
Best,
Tony Liu
 

HI, SUnnySkyGuy,
Thanks.
I have found a similiar design as attachment.
But its input IOP1 is too low, can you recommend a higher one?
I need IIP1 about -10dBm, BFP540 is too low, only -26dBm.
Best,
Tony Liu
 

Attachments

  • AN202 High Input Impedance LNA.pdf
    1.8 MB · Views: 190

Sorry, it should be "But its input IIP1 is too low, can you recommend a higher one?"
 

no I cant, but I imagine you need a low input range and cascade 50 ohm gain stages to avoid high impedance stray capacitance current effects on slew rate measured in <1V/ns

what is your application?
 
Hi, Sunny,
I don't care slew rate.
Just some application with slew rate 10V/ms, I guess it's enough.
I just care IIP1 higher.
Best,
Tony Liu
 

slew rate 10V/ms
Click to expand...
??? 600 MHz -10dBm corresponds to about 0.4V/ns slew rate...

At first sight, the level and input impedance requirements can be best met by an amplifier with internal feedback, a common drain buffer would be my first guess.
 
HI, FvM,
Many thanks for the explanation.
Actually, my freq is about 200M, so the slew rate is about 0.1V/ns from your method.
But 200M is the carrier wave, that is FM signal, and the IF signal is about 10KHz, so I guess the slew rate 6V/ms, right?
Best,
Tony LIU
 

tony_lth said:
HI, FvM,
Many thanks for the explanation.
Actually, my freq is about 200M, so the slew rate is about 0.1V/ns from your method.
But 200M is the carrier wave, that is FM signal, and the IF signal is about 10KHz, so I guess the slew rate 6V/ms, right?
Best,
Tony LIU
Click to expand...
The IF is a fixed freq. its's bandwidth may be low, but is not the slew rate of the IF output, the RF is higher, your question is now poorly defined without more details of the overall purpose and specs.

I suggest you read. more about LNA , RF amp, IF amp and radio designs.
 
Slew rate is a parameter of the instantaneous signal (modulated RF), not of the envelope.

I'm by the way missing a definition of "IIP1" or "IOP1" in my RF literature. Please explain.
 
Hi,
Sorry, IOP1 is a type error. Pls ignore it.
IIP1 is "Input IP1", just as "OIP1---Output IP1". What I mean is 1dB saturate point. Maybe it should be "IP1" or "OP1".
Best,
Tony Liu
 

Hi All
How about AD8045?
For 200M, it has gain=2, that is OK for me.
And it has a slew rate 1.35V/ns.
So I think it should be ok for my requirement.
Any comment?
Best,
Tony Liu
 

Attachments

  • AD8045.pdf
    502.3 KB · Views: 81

Hi, FvM,
Many thanks.
Could you recommend a FET as you foresaid " the level and input impedance requirements can be best met by an amplifier with internal feedback, a common drain buffer would be my first guess"?
I searched Triquint, Avago, etc. And found they almost don't produce FET now.
Best,
Tony Liu
 

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