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manfred

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wide-band LNA
Dec 05^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.

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aaron_do Senior Fellow Offline Posts: 1398	Re: wide-band LNA Reply #1 - 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
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manfred Junior Member Offline Posts: 15	Re: wide-band LNA Reply #2 - 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
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aaron_do

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Re: wide-band LNA
Reply #3 - 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

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there is no energy in matter other than that received from the environment - Nikola Tesla

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manfred Junior Member Offline Posts: 15	Re: wide-band LNA Reply #4 - Dec 10^th, 2008, 6:37am thanks Aaron! your reply is very helpful! cheers manfred
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