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Which value of bypass cap I should add in mW amplifier?

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TerryADS

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hi friends,
I want to design microwave amplifier,as 1.9 GHz LNA and power amplifier.Normal we add the bypass capacitor for the operating frequency on the power line,what else capacitor i should add?What criterion i should obey in pratical design?
Best&Regards
 

Not only do you want to keep the amplifier from putting signals into the power line, you want all signals on the power line to stay out of the amplifier because they could amplitude modulate the signal or produce IMD products.

Therefore higher value capacitors should be used and also ferrite series beads on the line.
 

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    TerryADS

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How can i measure whether my power line have amplitude modulate the signal?and whether can i
budget the case in simulation software as ADS?
 

Put an AC sine wave generator in series with the power line and do a frequency sweep or do several simulations at different lower frequencies. Do this with a sine wave generator at the desired signal frequency on the input of the amplifier. Then do a spectrum analysis of the amplifier output and look for sidebands on the desired signal or spurious spectral lines near your desired signal.
 

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    TerryADS

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flatulent said:
Put an AC sine wave generator in series with the power line and do a frequency sweep or do several simulations at different lower frequencies. Do this with a sine wave generator at the desired signal frequency on the input of the amplifier. Then do a spectrum analysis of the amplifier output and look for sidebands on the desired signal or spurious spectral lines near your desired signal.
Click to expand...

I hope, for safety sake, that you know he does not mean to connect sine wave generator to the power plug in the wall! You will die.
 

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    TerryADS

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Notice I said simulation. Mains operated power supplies have a hefty LC low pass filter at the input which gets rid of mains noise. I assumed that the question was about bypass capacitors on the B+ to the amplifier.
 

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    TerryADS

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