The Quality (Q) Factor of a capacitor is a unitless value which is equal to the capacitor’s reactance divided by the Equivalent Series Resistance (ESR) of the capacitor. As both reactance and ESR vary with changes in frequency, the Q value of a capacitor will also vary greatly with changes in frequency.
Most applications do not have to consider the Quality (Q) factor, and normal capacitors may be a good fit in those applications. However, the Q factor is one of the most important capacitor parameters in frequency dependent applications, like RF circuits. Most High Q capacitors generally used in high frequency applications are characterized by lower ESR values and lower losses.
- Q = 1/ DF
where Q is Quality Factor, DF is Dissipation Factor
- Q = Xc / ESR
wherer Xc = Capacitor Reactance, ESR = Equivalent Series Resistance (ESR) of the capacitor