decoupling and capacitor charge time question

hi
im a beginner. can anyone tell me what does decoupling means and how does it work. also how do we find the time when a fully charged capacitor will discharge.
with some examples if possible.
thanks

hi
A decoupling capacitor is used to de-couple(separate/isolate) the IC/Device from high frequency noise, which is generated by some switching operations internal to the IC. As u know that the reactance of the capacitor decreases as the frequency is increased, this property of capacitor bypasses the noice signal to ground. Proper care must be taken to choose the decoupling capacitor values.

And the discharging/charging time of the capacitor depends on the load to which it is connected. if it is resistor then the time constant of this combination gives the time to discarge/discharge (i.e. T=RC)

could u understand my explanation.

abdulahad100,
In digital applications, ICs draw significant amounts of current while switching. The sudden increase in current creates a voltage drop across the inductive reactance presented by the power supply traces. Decuplin g capacitors serve to provide a low impedance voltage source to supply these transient power supply currents.
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In analog applications, the inductive reactance of the power supply traces provides a potential positive feedback path from the output of the analog IC throught the power supply. This feedback is a potential source of osillations. The decoupling path reduces the voltage that is induced into the power supply traces, by providing a low impedance path to signal ground.
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In both applications, the simplified equation to use is
(Delta V) = (i * (Delta T))/(C). where
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Delta V is the magnitude of the voltage change
i is the magnitude of the transient current.
C = decoupling capacitance
Delta T is the duration of the current pulse.
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This is an over-smplification, since the transient current is not a nice square pulse. However, you can come up with a conservative design using this formula. It does, however, require a knowledge of the transient current amplitude and duration.
Regards,
Kral

thanks
that really helped.
i don't know much about inductive reactance and the stuff but i get the basic idea.