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RE: BTW ...

Posted by 13th Duke of Wymbourne (A) on January 3, 2025 at 11:12:47

In Reply to: RE: BTW ... posted by andyr on January 1, 2025 at 19:01:15:

I would not expect the follower noise to be significant. In cascaded stages the source noise gets amplified down the chain and each stage adds its own noise but the noise floor is raised with each stage of amplification hence succeeding stage noise requirements are relaxed. The first stage is the most important and in communication systems the first stage is always a low noise amplifier (LNA).
For simplicity, let's ignore the amplifier noise floor and just think about the noise of the signal source. If it is a LOMC the source resistance is ~ 10ohms and the noise of that resisitance will get amplified. Assuming you have at least 40dB of voltage gain (100x), the noise power after amplification will be equivalent to a resistor of 10*100*100 = 100k. I cannot imagine your follower producing anywhere near that level of noise (datasheet says it has 2dB noise figure referenced to 2kohms that means it is bit noisier than a 2k resistor). So, a mystery that you could decipher using spice noise analysis or just enjoy another LP

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