TDA5255E1_07 Datasheet, PDF (39/91 Pages) Infineon Technologies AG – ASK/FSK 434MHz Wireless Transceiver

Measured Magnitude of S11 of evalboard:
TDA5255 E1
Version 1.2
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
=

−20 * log_1 −

Q_L
Q_U



=
−20
*

log_1
−

6,8
32



=
2dB
[3 – 4]
Data Sheet
39
2007-02-26