Working

• Common mode capacitors work under disturbed conditions such as unwanted electric signals. The signals are called electromagnetic interference (EMI) and occur at high frequencies. The EMI occurs in two modes: namely, radiated noise and conducted noise. Under conducted noise, there are two modes generally; differential mode (DM) and common mode (CM).
  
  

Y Capacitor

• One form of attenuating EMI in the common mode is by using a Y capacitor. This capacitor is connected between the primary return terminal (PRTN) and secondary return terminal (SRTN) of the supply of power. The connection of the Y capacitor between the two terminals is the position that best reduces the level of EMI.
  
  

Noise

• In transformers, Y capacitors reduce the common-mode noise by diverting a portion of the noise current off the route of the Line Impedance Stabilization Network. The main aim of this is to prevent the EMI from getting access to the mains port, a problem that can lead to mishaps in the whole circuit and its power source.
  
  

Low-Voltage Technique

• Another method of use of common mode capacitors is the low-voltage unity-gain-reset (UGR) technique. It is used to correct the imbalances of charge caused by saturation of a given charge in the circuit. A measure to correct this is the introduction of a set of capacitors to help correct the imbalances in the charge passing through the circuit. This set of capacitors constitutes the common-mode feedback circuit, responsible for the correction of the charge imbalance.
  
  

Pseudo-Differential Integrator

• Using the pseudo-differential integrator, three capacitors are used to correct the common mode problem. Two of them provide the negative charge while one enhances neutralization by discharging the negative charge to ground. Another set of two capacitors are fixed to either terminals. One is the DC offset correction circuit and the other functions as the floating reference, preventing the output from reaching the ground while simply resetting it. The common mode capacitors are thus important in the correction of common mode errors in different circuits.