TDA5251F1 Datasheet, PDF (39/88 Pages) Infineon Technologies AG – ASK/FSK 315MHz Wireless Transceiver

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Measured Magnitude of S11 of evalboard:
TDA5251 F1
Version 1.0
Application
S11_measured_315.pcx.
Figure 3-3 S11 measured
Above you can see the measured S11 of the evalboard. The –3dB-points are at 288MHz and
344MHz. So the 3dB-bandwidth is:
B = fU - f _L = 344 MHz - 288 MHz = 56 MHz
[3 – 1]
The loaded Q of the resonant circuit is:
QL =
f _center
B
=
315 MHz
56 MHz
= 5,6
[3 – 2]
The unloaded Q of the resonant circuit is equal to the Q of the inductor due to its losses.
QU = Q _INDUCTOR » 27 @ 315 MHz
[3 – 3]
An approximation of the losses of the input matching network can be made with the formula:
LOSS
é
= -20 * log ê1 -
êë
QL
QU
ù
ú
=
-20
*
log _êé1 -
úû
êë
5,6
27
ù
ú
úû
=
2 dB
[3 – 4]
Preliminary Specification
39
2003-02-18