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Why to match thr first stage to a specific impedance (50ohms)?? (Read 4925 times)

zhangjerome Community Member Offline Posts: 42	Why to match thr first stage to a specific impedance (50ohms)?? Jul 11^th, 2008, 6:42pm what's the drawback if it's not matched to 50 ohms??
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pancho_hideboo

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Re: Why to match thr first stage to a specific impedance (50ohms)??
Reply #1 - Jul 11^th, 2008, 10:41pm

zhangjerome wrote on Jul 11^th, 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

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zhangjerome Community Member Offline Posts: 42	Re: Why to match thr first stage to a specific impedance (50ohms)?? Reply #2 - Jul 12^th, 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??
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pancho_hideboo

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Re: Why to match thr first stage to a specific impedance (50ohms)??
Reply #3 - Jul 12^th, 2008, 7:05am

zhangjerome wrote on Jul 12^th, 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

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zhangjerome Community Member Offline Posts: 42	Re: Why to match thr first stage to a specific impedance (50ohms)?? Reply #4 - Jul 12^th, 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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