Coupling vs Decoupling

The capacitor is a basic electronic component capable of storing electric charges. It is made of an insulator attached by 2 metal plates on both sides. Today we will know about 2 important use cases of capacitors. But first a reminder, do not get confused by bringing on the concept of AC capacitor (non-polar) here. Just think that we are talking about DC capacitor (polar) only. 

Decoupling capacitors: 

Until Capacitor is fully charged Direct Current can flow through the capacitor for a short period of time. The idea is to use the capacitor in such a way that it shunts/is connected in parallel. 

• They oppose quick change of voltage.
• They are used to filter out the AC component  
• Decoupling capacitors added to the circuit in order to smooth out the power supply voltage.
  
• An alternative name is bypass capacitor. 

Coupling capacitors:

Alternating current switches it's direction with a certain interval thus making the capacitor charged and discharged. So if the capacitor is connected in Series AC will flow through the capacitor. 

• Used to filter out the DC component of the signal
• In analog circuits, coupling capacitors are extensively used in amplifiers. 
• The voltage bias of a transistor is crucial for the normal operation of the amplifier. ac signal is fed to the base of a transistor where the capacitor is in series (this mode is called coupling ). 
• The role of coupling capacitors is to prevent the incoming AC signal from interfering with the bias voltage applied to the base of a transistor.