TDA5255E1 Datasheet, PDF (39/93 Pages) Infineon Technologies AG – ASK/FSK 434MHz Wireless Transceiver

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Measured Magnitude of S11 of evalboard:
TDA5255 E1
Version 1.1
Application
S11_measured_434.pcx.
Figure 3-3 S11 measured
Above you can see the measured S11 of the evalboard. The –3dB-points are at 404MHz and
468MHz. So the 3dB-bandwidth is:
B = f_U - f_L = 468MHz - 404MHz = 64MHz
[3 – 1]
The loaded Q of the resonant circuit is:
Q_L =
f_center
B
=
434,2MHz
64MHz
= 6,8
[3 – 2]
The unloaded Q of the resonant circuit is equal to the Q of the inductor due to its losses.
Q_U = Q_INDUCTOR » 32@434MHz
[3 – 3]
An approximation of the losses of the input matching network can be made with the formula:
LOSS
=
é
-20 * log_ê1 -
êë
Q_L
Q_U
ù
ú
úû
=
-20 * log_êëé1 -
6,8
32
ù
úû
=
2dB
[3 – 4]
Preliminary Specification
39
2002-11-28