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Design >> RF Design >> wide-band LNA
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Message started by manfred on Dec 5^th, 2008, 9:54am

Title: wide-band LNA
Post by manfred on Dec 5^th, 2008, 9:54am

Hi, everyone!

I'm designing a wideband LNA(about 1~1.8GHz) in cascode structure,but I wonder how to desing the input and output match network?
in my opinion, the input match network can be reallized with LC-ladder(bandpass filter), but I don't know if it is the best way.

as the output of LNA will connect to the offchip SAW filter, so the output match is required. I adopt the emiter follower and output match network, but I think the whole LNA is too complicated and the power is a bit large.
are there any other simple solutions?

anyone is appreciable
Best regards.

Title: Re: wide-band LNA
Post by aaron_do on Dec 7^th, 2008, 5:35pm

Hi,

for the input matching, have you considered just using resistive feedback, or a common-gate input?

cheers,
Aaron

Title: Re: wide-band LNA
Post by manfred on Dec 8^th, 2008, 3:15am

Aaron:
I have thought about resitive feedback and common-base input, but it seems the NF is a bit large .
so I select the usual structur of source degeneration plus LC-ladder filter .
Have you ever designed resistive feedback or common-base input LNA wich supply good NF performance?

cheers

manfred

Title: Re: wide-band LNA
Post by aaron_do on Dec 9^th, 2008, 5:19pm

Hi,

i personally have not, but i've read some papers on wideband amplifiers with NF less than 3 dB using those methods. If you want better than that then i guess you will need to go with common-source. Just wondering though, i calculated the Q you require is about 1.67. So perhaps you can just go with a standard inductive source degeneration LNA and still get enough bandwidth.

Not sure if it will help but there is a paper you might find useful if you intend to go for ladder filter design. It used just three inductors total and had a very broad matching bandwidth...

Aly Ismail, Asad A. Abidi, "A 3–10-GHz Low-Noise Amplifier With Wideband LC-Ladder Matching Network" JSSC vol. 39, no. 2, dec 2004.

cheers,
Aaron

Title: Re: wide-band LNA
Post by manfred on Dec 10^th, 2008, 6:37am

thanks Aaron!

your reply is very helpful!

cheers

manfred