Post subject: decoupling and coupling.. Posted: Fri Apr
21, 2006 3:50 am
Joined: Sun Apr 09, 2006
good day everybody,
Can anybody explanain definition of coupling and decoupling?
what is their's purpose? how is their connection in RF matching
Posted: Fri Apr 21, 2006 8:33 am
Mon Jun 27, 2005 2:02 pm
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.
Post subject: Posted: Fri Apr 21,
2006 9:11 am
Joined: Sun Aug 03, 2003
Location: Erie, PA
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.
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