# A question of LNA - RF Cafe Forums

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czc2166

Post subject: A question of LNA Posted: Thu Mar 30, 2006 9:47 am

Lieutenant

Joined: Thu Mar 30, 2006 9:20 am

Posts: 1

Hello ,I'm a student and know a little ADS .I'm designing the LNA.When I have mathed input and output impedance using the L and C,I can design the PCB .But the appliances should't link directly to each other .there are shuold be the transmission line between them .How should I decide the transmission line width and length .How do I measure The influence of the ransmission line .Should the input and output impedanc be changed??[/url]

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IR

Post subject: Posted: Thu Mar 30, 2006 5:37 pm

Joined: Mon Jun 27, 2005 2:02 pm

Posts: 373

Location: Germany

Hello czc2166,

When designing a matching circuit you should take into consideration the transmission lines that connect between the matching components. In general, these transmission lines should have an impedance of 50 ohm. You can calculate the width of the line by using LINECalc (A tool of ADS), or just by using a formula (Depednding on the type of transmission line you use - Co-Planar, µstrip etc). Series transmission lines (50 ohm) will add delay (phase angle), you will see it on the smith chart. The impedances will be changed of course, but you can tune the values of the components to compensate for that. Also take into consideration that the components have tolerance. Finally see that the matching circuit provides the required matching all over the required BW.

What is your operating frequency and BW??

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Best regards,

- IR

Posted  11/12/2012