Re: RLC
- From: "Andrew Holme" <ajholme@xxxxxxxxxxx>
- Date: 8 Apr 2005 01:28:29 -0700
jason wrote:
> Yes that's right Garth ,.. Thank you
>
> Sometimes in some cases, we compare the reactance of a capacitor with
> resistance of a resistance like the below case
>
> 1/wC << Rs
>
> So my question is , what does it mean by this comparison?
> reactance < resistance
>
> What does it tell us?
>
> Should not we compare resistance with resistance
> while comparing reactance with reactance
> Both of them have the unit ohm?
>
> What is the implication of using such a comparison , what does it
tell
> us?
>
> Thank you
When using AC-coupling between stages, the coupling capacitors can form
unwanted high-pass filters, unless the reactance is negligible compared
to the source resistance.
Consider the RC high-pass filter:
----C-----+---
|
R
|
----------+---
Transfer function = sCR / (1+sCR)
At high frequencies Vout/Vin = 1 and phase = 0;
At the break-point, phase is 45 degrees and output is 3dB down;
Below the break-frequency, output falls at -20dB per decade.
The break frequency is w = 1/RC
So, Vout/Vin = 1 when 1/wC << R
.
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