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decoupling and coupling.. - RF Cafe Forums
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ngks79
Post subject: decoupling and coupling.. Posted: Fri Apr 21,
2006 3:50 am
Lieutenant
Joined: Sun Apr 09, 2006 8:48
pm
Posts: 2
Location: Penang
good day everybody,
Can
anybody explanain definition of coupling and decoupling? what is their's
purpose? how is their connection in RF matching circuit?
Thanks
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IR
Post subject: Posted: Fri Apr 21, 2006 8:33
am
Site Admin
Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373
Location: Germany
Hello ngks79,
AC or RF coupling
is done with a series capacitor which its purpose is to deliver only
the alternating or high frequency signal and block the DC in order not
to vary the operating point of the active device (Usually transistor
or amplifier). These series capacitors are often connected between a
matching network and the input or output of the device. Their capacitance
should be calculated in a way that their reactance is low in the lowest
frequency of operation (not more than few ohms).
Decoupling means
suppressing high frequency signals, this is usually done in supply voltages
by connecting capacitors between the supply and GND rails. The capacitors
short high-frequency signals (Interferers and noise) to GND.
_________________
Best regards,
- IR
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Kirt Blattenberger
Post subject: Posted: Fri Apr 21, 2006 9:11
am
Site Admin
Joined: Sun Aug 03, 2003 2:02 pm
Posts: 308
Location: Erie, PA
Greetings:
A similar question
was asked of me the other day at work on a related topic, and that was:
What is the difference between a decoupling capacitor and a bypass capacitor?
The questioner had been told by his college professor that a decoupling
capacitor was used in series with an RF signal to block DC, and that
a bypass capacitor was used on DC supply lines to shunt AC to ground.
IR's response is in line with my own usage of the term "coupling
capacitor" for one used to pass RF and block DC. The terms "decoupling
capacitor" and "bypass capacitor" are used interchangeably almost universally
in technical literature and on all of the online electronics dictionaries
(and app notes) I checked. Both terms describe a capacitor used to conduct
AC to ground, or at least away from the signal path.
…just another
data point.
_________________
- Kirt Blattenberger
RF
Cafe Progenitor & Webmaster
Posted
11/12/2012
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