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What is the RF choke function in this circuit?

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ssayan79

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Hi to all
i have a problem with a choke rf. I must study the circuit a have attached for my exam, but i don't know why an inductor as a choke is placed in this way.
Please help me.
 

Re: Choke Rf

RF chokes are used to supply a short circuit path for DC and high impedance for AC signals. The RFC used at this circuit is to connect the p-terminal of the diode to the supply to bias the diode into certain operating point (short circuit for DC). If it was connected directly to the supply, this would cause the output node to be seen as AC ground, so a coil is used to have high impedance at the AC signal's frequency to avoid shunting the AC signal to the DC supply.
 

Re: Choke Rf

Thak you very much.
But in this configuration my diode has, in DC, both terminals to ground. Is it no shorted in this case??
 

Re: Choke Rf

I think that at this case, you want to have zero V across the diode (to be reverse biased perhaps). If the RFC was removed and diode was connected directly to the ground, your AC signal will be shunted to the ground. This circuit may function as a limiter, when the AC signal amplitude exceeds the diode's cut-in voltage, the diode will be forward biased and signal's amplitude will be clipped.
 

Re: Choke Rf

Thank you very much
you are very clear. I have the ultimate question. In the model of the diode i hav found that if the forward voltage exceeds 0.7V, diode begins to conduct. I have not clear why when AC signal amplitude exceeds the diode's cut-in voltage, diode behaves as a limiter and where i could find mathematic model of this behaviour.
Thank you
 

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