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Design >> RF Design >> Why to match thr first stage to a specific impedance (50ohms)??
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Message started by zhangjerome on Jul 11th, 2008, 6:42pm

Title: Why to match thr first stage to a specific impedance (50ohms)??
Post by zhangjerome on Jul 11th, 2008, 6:42pm
what's the drawback if it's not matched to 50 ohms??

Title: Re: Why to match thr first stage to a specific impedance (50ohms)??
Post by pancho_hideboo on Jul 11th, 2008, 10:41pm

zhangjerome wrote on Jul 11th, 2008, 6:42pm:
what's the drawback if it's not matched to 50 ohms??

Your description is not sufficient.
What do you mean by first stage ?
What component or signal is connected to first stage as input ?
If any component such as BPF or anttena is connected, what value of its output impedance ?

See my post in http://www.designers-guide.org/Forum/YaBB.pl?num=1195659245

Title: Re: Why to match thr first stage to a specific impedance (50ohms)??
Post by zhangjerome on Jul 12th, 2008, 5:11am
By first stage I mean a low noise amplifer in the RF receiver chain. What will happen if this low noise amplifier is not well matched to a 50 ohms impedance? I know there is going to be reflection. How does this relfection degrade the receiver performance??
 

Title: Re: Why to match thr first stage to a specific impedance (50ohms)??
Post by pancho_hideboo on Jul 12th, 2008, 7:05am

zhangjerome wrote on Jul 12th, 2008, 5:11am:
By first stage I mean a low noise amplifer in the RF receiver chain. What will happen if this low noise amplifier is not well matched to a 50 ohms impedance? I know there is going to be reflection. How does this relfection degrade the receiver performance?

Gain(S21) is reduced. Then total NF of RX system will be degraded.

Maybe you don't understand various gains such as transducer gain, power gain, voltage gain, available power gain, maximum available power gain.

Cadence's Tool player often encounter same confusion.

http://www.designers-guide.org/Forum/YaBB.pl?num=1202753208/13#13

Title: Re: Why to match thr first stage to a specific impedance (50ohms)??
Post by zhangjerome on Jul 12th, 2008, 10:18pm
Thank you, Pancho.
You are right. I just confused by those gain definitions and the gain given by Spectre.


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