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  1. #1
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    decoupling capacitor

    Hi all,
    Can any one explain comprehensively , what are the major differences between a Decoupling capacitor, Bypass capacitor and Filter capacitor, I mean the Functional diffrences.

    Also it would be very nice if any one can explain what are the basic diffrence between an Inductor and a ferrite bead, again functional diffrences

    best regards

    •   Alt8th July 2009, 12:00

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    capacitor bypass

    Physically, all the capacitors are same, only their functionaliyt is application specific.
    When capacitor is used in between two stages for removing the DC components from the signal, it is called coupling/decoupling capacitor.
    When capacitor is used to bypass the AC signal component across any circuit, it is called bypass capacitor.
    And when the capacitor is used with respect to ground i.e. one of its end is conected to ground, it works like filter capacitor.


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    •   Alt8th July 2009, 12:10

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    best capacitor for filters

    The bypass capacitor and the decoupling capacitor are functionally the same because capacitors can bypass or decouple only when they are connected across the load. For instance to avoid noise spikes(ac) from affecting a dc load often a cap is placed across the load for proper operation.

    IF caps are connected in series they are called coupling/decoupling capacitors.. bcoz they couple ac from 1 stage to another and decouple the dc from going to the next stage as in multistage amplifiers.



    •   Alt8th July 2009, 13:11

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  4. #4
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    decoupling cap

    Quote Originally Posted by nirajvlsi
    Hi all,
    What are the major differences between a Decoupling capacitor, Bypass capacitor and Filter capacitor, I mean the Functional diffrences.

    Also it would be very nice if any one can explain what are the basic diffrence between an Inductor and a ferrite bead, again functional diffrences

    best regards
    Capacitors allow AC and do not allow DC to pass through them. The impedance given by
    z = 1 /(2ΠfC)
    f is the frequency of AC in Hz and C is the capacitance in Farads. Non AC signals can be expressed as a sum of sinosoidal waves.
    It is the matter of nature of application (actually terminology) what term you use from the three quoted (Decoupling capacitor, Bypass capacitor and Filter capacitor)
    If two stages are to be isolated from each other by not allowing AC from one stage to the other, a capacitor is connected to ground from the point where input of one stage enters the next stage. Thus the AC coupling between the two stages is eleminated (reduced), thus it can be called a decoupling capacitor. If I describe it by saying I have bypassed all the AC component from one stage to ground not allowing it to enter the next stage, it is the bypass capacitor. It can be called a filter capacitor if I view at the situation as if all the AC component from an earlier stage is filterd (sent to ground) preventing it from entering the next stage. Thus it is crudely the matter of terminlogy.
    Ferrite is a material that is used as the core while making inductors working at higher frequencies instead of iron core. Ferrite core or ferrite beed inductor is the inductor designed to work at higher frequencies. This is where it differs from an iron core inductor.
    Hope this clarifies the issue.
    Regards



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