What are impedance/
ESR frequency characteristics in capacitors?

2/14/2013
Basic

Category: Capacitor Room
3.Frequency characteristics of multilayer ceramic capacitors
 There are also different types of multilayer ceramic capacitors made of different materials and with different shapes. Let's look at how these factors affect frequency characteristics.
(1) ESR
ESR in the capacitive region depends on dielectric loss caused by the dielectric material. Class 2 high dielectric constant materials tend to have higher ESR levels as they use ferroelectrics. Class 1 temperature compensation materials use paraelectrics, and therefore exhibit very little dielectric loss and have low ESR levels.
In addition to the resistivity of the electrode material, the shape of the electrode (thickness, length, width) and the number of layers, ESR levels at high frequencies from around the resonance point to the inductive region are also influenced by the skin effect and by the proximity effect. Ni is often used as the electrode material, but Cu that has low resistivity is sometimes chosen for low loss-type capacitors.

(2) ESL
  ESL of multilayer ceramic capacitors is strongly affected by the internal electrode structure. Where the size of the internal electrode is shown as length l, width w and thickness d, the inductance ESL of the electrode can be shown by formula (3), according to F. W. Grover.

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  From this formula, it is apparent that ESL decreases as capacitor electrodes become shorter, wider and thicker.
  Figure 6 shows the relationship between the nominal capacity and self-resonant frequency for different sizes of multilayer ceramic capacitors. You can see that, as size decreases, self-resonant frequency increases and ESL decreases for the same capacity. This means that small capacitors with a short length l are best-suited to high-frequency applications. 

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Figure 6.
The relationship between nominal capacity and
self-resonant frequency for different sizes


  Figure 7 shows an LW reverse capacitor with a short length l and large width w. From the frequency characteristics shown in Figure 8, you can see that LW reverse capacitors have lower impedance and better characteristics than a conventional capacitor of the same capacity. By using LW reverse capacitors, the same performance can be achieved as that of conventional capacitors with a fewer number of units. The reduction of unit number enables reduced costs and a reduction of mounting space.
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Figure 7. External appearance of an LW reverse capacitor 

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Figure 8. |Z|/ESR of an LW reverse capacitor and a general-purpose capacitor


4.How to obtain frequency characteristics data
  While data on frequency characteristics can be obtained using an impedance analyzer or vector network analyzer, such data is also now available on the websites of parts manufacturers. 
  Figure 9 shows a screen view of Murata's "SimSurfing" design tool. Characteristics can be displayed by simply entering the model number and the items you wish to check. Furthermore, you can download SPICE network lists and S2P data as data for simulations. Feel free to use these for design of all types of electronic circuits.

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Figure 9. An example screen view of the "SimSurfing" design tool
(Click the image to see the enlarged image)


See here for SimSurfing


Person in charge: A.S., Components Business Unit, Murata Manufacturing Co., Ltd.