# In PA, if the bias is VDD then how can swing be 2*VDD with inductive load

1. ## In PA, if the bias is VDD then how can swing be 2*VDD with inductive load

Hi, From the below link I read that when we have inductive load, for example, in CS amplifier the output voltage swing can be (2*VDD), if VDD is the supply voltage

"For the inductive load, the DC voltage at drain is equal to Vdd. And so the maximum negative voltage swing is from VDD to 0V.
And so in order to keep the waveform symmetrical we "limit" the positive voltage swing to 2VDD (swing from Vdd to 2Vdd)." - Copied from comments section.

My question is that could the signal swing can go beyond the supply voltage? I always thought the supply is the maximum limit both including DC+Signal (AC). Please someone explain.

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2. ## Re: In PA, if the bias is VDD then how can swing be 2*VDD with inductive load

Originally Posted by circuitslave
My question is that could the signal swing can go beyond the supply voltage?
Too easy.

Vout=Vdd - L*dI/dt

Surely learn very basic things before EDA Tool Play.

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3. ## Re: In PA, if the bias is VDD then how can swing be 2*VDD with inductive load

Originally Posted by circuitking

"For the inductive load, the DC voltage at drain is equal to Vdd. And so the maximum negative voltage swing is from VDD to 0V.
And so in order to keep the waveform symmetrical we "limit" the positive voltage swing to 2VDD (swing from Vdd to 2Vdd)." - Copied from comments section.
You have the explanation there.

If you want more insight into such behavior, refer to "Pulse, Digital and Switching Waveform" by Millman and Taub.

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