Basics of capacitors [Lesson 2]
What kind of characteristics do capacitors exhibit?
4 14, 2011
Category: Capacitor Room
【Lesson 2: Ceramic capacitor functions and characteristics】
Lesson 1 introduced how capacitors work. This lesson introduces the characteristics of capacitors.
1-1. Capacitor types
There are various types of capacitors. As shown in Fig. 1, capacitors are classified according to the materials used, such as ceramic capacitors, tantalum electrolytic capacitors, and aluminum electrolytic capacitors. Monolithic ceramic capacitors in particular are compact and also have a wide capacitance range, so they are used in various circuits such as noise removal, supply voltage smoothing, and filters. Recently, they have become essential components for realizing advanced functions for mobile phones and TV sets.
1-2. Features of monolithic ceramic capacitors
<Characteristic 1 Temperature characteristics>
Ceramic capacitors are divided into temperature-compensating types and high dielectric constant types as shown in Fig. 2. The change in electrostatic capacitance due to temperature differs for each type, so they must be used in accordance with their features. These capacitors are classified into detailed categories by the JIS Standard in Japan, and the EIA Standard in Europe.
Temperature-compensating capacitors feature a small rate of change in the electrostatic capacitance as the temperature changes, and are used for applications such as filters and high-frequency circuit matching. These capacitors are sometimes used in combination with coils, but the coil properties are such that the inductance increases as the temperature rises, so there are also cases where the capacitors are given negative temperature characteristics and used to compensate the offset.
-High dielectric constant types
High dielectric constant capacitors use materials with a high dielectric constant, and feature a large electrostatic capacitance. They are used for applications such as power supply decoupling capacitors and smoothing circuits. These capacitors have a large rate of change in electrostatic capacitance due to temperature compared to temperature-compensating capacitors, so care must be taken for use in filters and other signal paths.
<Characteristic 2 Low ESR and Low ESL>
Monolithic ceramic capacitors feature good high-frequency characteristics. Compared to other types of capacitors, the structure enables a smaller resistance component (ESR※1) and residual inductance component （ESL※2）, so capacitor functions can be maintained even at high frequencies. Fig. 3 and Fig. 4 show the equivalent circuits and impedance characteristics. Aluminum electrolytic capacitors and tantalum electrolytic capacitors have a high ESR component, so the impedance is also high. However, the ceramic capacitor impedance decreases as the frequency increases. This is effective for removing noise, and also enables configuration of high-performance filters.
※1 ESR： Equivalent Series Resistance
※2 ESL： Equivalent Series Inductance
Person in charge: Murata Manufacturing Co., Ltd. M.N & Y.I