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What's the balanced amplifier noise figure

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jayleung

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Hi, I have a question about calculating the noise figure of a balanced amplifier circuit, as shown in the attachment.

In this case, two LNA is followed by a 90-deg hybrid coupler splitter, and one more 90-deg hybrid coupler combiner is used to combine the signals. If assume the gain and noise are the same for two LNA, and the hybrid couplers have about 0.5 dB loss, how can I calculate the noise figure of the whole circuit?

One more issue is that whether the terminating resistors contribute additional noise to the circuit output?

Thanks in advanced
 
I am wondering how can I calculate that? Are there any formula to do so?

The other issue is that why the matching resistors do not contibute addtional noise to the output? If these resistors is hotter (due to the heat dissipation), are there any negative effects? If yes, how can it be accounted to the noise calculation?

thanks
 

In real life the NF of a balanced amplifier is approximately 25% greater than the NF of a similar single amplifier.
 

if you put the simulator then it will account all the effects.
theory calculations can not handle this big problem. this is linked with probability.
 

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    jayleung

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