Passive components

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Doc ID 023704 Rev 1

resonant circuit. Typically, for a 1.6 mm thickness PCB material, a single via can add 1.2 nH

of inductance and 0.5 pF of capacitance, depending on the via dimensions and PCB

dielectric material, although the effects can be minimized by ensuring that the inter-via

spacing is of

λ/30.

3

Passive components

Passive components play a fundamental rule in the success of an ideal PCB. The following

is a brief description of the physical properties of the capacitor and inductor components

that can help with the circuit design and the choice of the components.

ST strongly recommends using only the values and types of items specified in the BOM of

the SPIRIT1 application board, since a change in their value and/or type can create a

different behavior of the RF characteristic of the application.

3.1

Capacitors

A capacitor is a passive electrical component used to store energy in an electrical field. The

forms of practical capacitors vary widely, but all contain at least two electrical conductors

separated by a dielectric.

Capacitors differ from each other in construction techniques and materials used in the

manufacture. A lot of different types of capacitors exist (double-layer, polyester,

polypropylene and so on), but this document focuses on the surface mount versions of

ceramics only. The other types of capacitors are not indicated for the application targeted in

this document.

A capacitor, as a practical device, exhibits not only capacitance but also resistance and

inductance. A simplified schematic for the equivalent circuit is shown in Figure 5.

Figure 5.

Capacitor equivalent circuit

Typically, the ESR (equivalent series resistance) and the ESL (equivalent series inductance)

are defined for the capacitors. The term ESR combines all losses, both series and parallel,

in a capacitor at a given frequency so that the equivalent circuit is reduced to a simple R-C

series connection. The same is true for the ESL which is the equivalent series inductor

Rp

C

Rs

L

AM14766V1