101SHT100AS1LE datasheet(7/34 Pages) EXXELIA

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CERAMIC CAPACITORS

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General characteristics

Page revised 06/20

The plot of the theoretical expression (5) of the impedance of a Single Layer

Capacitor is shown in Fig. 8. As one can see, this theoretical curve predicts

a double inﬁnity of self-resonant frequencies (alternances of serial and

parallel resonances) that are identical to the ones encountered in real world

measurements.

Consequently, for predicting and understanding the behavior or a capacitor at

frequencies that are close or above the ﬁrst SRF, the lumped model (shown

in Fig. 1) is not applicable and must be replaced by the distributed model or

transmission line model (shown in Fig. 7).

Furthermore, according to [1], the transmission line model predicts accurately

that the serial or parallel self-resonances are doubled when a capacitor chip

is mounted with its internal electrodes oriented vertically (once again, it is

impossible to predict such a phenomenon with the lumped model).

If now we take a closer look at a capacitor used as a coupling capacitor in a

wide band application, it is evident when looking at ﬁg. 8 that the coupling

function will be correctly fulﬁlled at frequencies close to the serial resonant

frequencies, since the capacitor’s impedance is very low.

Conversely, the contrary will be encountered at the parallel resonant

frequencies since the capacitor’s impedance is very high and consequently

the coupling function is not fulﬁlled.

Therefore in the application we must avoid to be at PRF. The High ESR may

involve power loss and increase of internal temperature, since:

∆T

RTH

P =

(stationary state) (7)

P = ESR I2 (6)

The temperature increase is therefore:

∆T = ESR I2 RTH (8)

Where Rth is the thermal resistance of the capacitor with the PCB.

At ﬁrst glance, equations (6), (7) & (8) conﬁrm an increase of the internal

temperature, but a closer look at these equations reveals that this temperature

rise takes place only if the current I is constant. The problem is that in real

applications the power source is rarely a pure current generator. More often

than none, the power source is the dual of a current generator ie. a pure voltage

generator. In the case of a circuit powered by a pure voltage generator, the

contrary of the preceding behavior will be encountered at PRF since, as the

capacitor’s impedance is very high, the current I is very low and consequently,

according to (6), (7) & (8) the temperature rise is not obvious or may be a

temperature fall.

From these considerations, one can draw the conclusion that when a coupling

capacitor is used at its PRF, for predicting an eventual temperature rise it is

also mandatory to know for the PRF the behavior of the generator and the load

between which the coupling capacitor is serially inserted.

In other words, the coupling capacitor is not the only cause of a temperature

rise and consequently, the characteristics of the whole circuitry must be well

known and understood prior to investigate the reasons of a temperature rise.

Frequency (GHz)

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

S11m

(2.62, 0.00)

Figure 4: S11curve for a 251SHF150 from EXXELIA ABC software

0.2

0.4

0.6

0.8

Frequency (GHz)

1.2

S21m

(3.64,0.26)

Figure 5: S21curve for a 251SHF150 from EXXELIA ABC software

0.01

Frequency (GHz)

1000

100

0.1

ESR

(3.64, 283.79)

Figure 6: ESR curve for a 251SHF150 from EXXELIA ABC software

General Information

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