NXP Semiconductors
JN-RM-2079
QN9090 module development reference manual
JN-RM-2079
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© NXP Semiconductors N.V. 2020. All rights reserved.
Reference manual
Rev. 1.0
— 17 Jan 2020
11 of 31
For most component suppliers, this quality is expressed by the Self Resonant
Frequency (SRF) specification. For example, a capacitor has parasitic inductance
introduced by the metal leads of the components. As frequency increases, at some
point the impedance due to the parasitic inductance is greater than the impedance of
the capacitor, and at that frequency and higher, the component no longer acts as a
capacitor and now acts as an inductor. At the point at which the impedance from both
inductive and capacitive components is the same, the part will resonate as a LC
parallel resonant circuit, and this is called the Self Resonant frequency. Fig 6 shows
some typical response curve.
Fig 6. RF Plots for 3pF ceramic capacitor Murata GRM1555 type
The same is true of inductors. There is parasitic capacitance in an inductor, mainly due
to capacitive coupling between the turns of wire. At some point in frequency, this
capacitance will have a higher impedance than the inductance of the part. From this
frequency and higher the part acts as a capacitor and not as an inductor.
The Bill of Materials (BOM) is available for all NXP reference designs. The BOM
shows the specific vendors and part numbers used on NXP designs. It is certainly
possible to substitute another vendor's parts, but it may impact the performance of the
circuit, therefore, it may be necessary to use different component values when parts
from another vendor are used.
If there is a performance issue on a new design, and part substitutions were made on
that design, then it is strongly recommended that components identical to those used
in the NXP reference design be placed on the new design for test purposes. Once the
design is working properly with components that are identical to those used by NXP,
then it will be possible to substitute components from other vendors one at a time, and
test for any impact on circuit performance.
