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Design >> RF Design >> LNA's Noise Figure
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Message started by DDC on Jun 17^th, 2013, 5:04am

Title: LNA's Noise Figure
Post by DDC on Jun 17^th, 2013, 5:04am

Hello,

I simulated the noise figure of a lna in cadence spectre, on time with s-parameter analysis and a second time with noise analysis. It seems that when I use voltage at the output and input port with 50 Ohm the noise differs from that of the s-parameter analysis, where I choosed an input and an output port. Only when I use also the port as output probe in noise analysis the noise figures are the same. Can somebody tell me why is there a difference between the noise figures of the 2 analysis ? Thanks for response.

Title: Re: LNA's Noise Figure
Post by rfidea on Jun 17^th, 2013, 11:05am

I can think of two reasons.

1. When you say you have a voltage as output does you load the LNA with a resistor? If not the different loads can of course give different noise figure.

2. If you load the LNA output with a resistor when not using a port the noise from that resistor will be included in the noise sum. The same noise from the port is not part of the noise sum, per definition of noise figure.

Title: Re: LNA's Noise Figure
Post by DDC on Jun 19^th, 2013, 6:24am

I loaded also the transistor with a 50 Ohm noisefree resistor. There is always the same effect.