TDA5250D2_07 INFINEON [Infineon Technologies AG], TDA5250D2_07 Datasheet - Page 45

• Manufacturer Part Number: TDA5250D2_07
• Description: ASK/FSK 868MHz Wireless Transceiver
• Manufacturer: INFINEON [Infineon Technologies AG]

The diagram of Figure 3-7 has been measured directly at the PA-output at V
the matching circuit of about 2dB will decrease the output power. As shown in the diagram, 240
Ohm is the optimum impedance for operation at 3V. For an approximation of R
other supply voltages those 2 formulas can be used:
and
Figure 3-7
The DC collector current I c of the power amplifier and the RF output power P o vary with the load
resistor R L . This is typical for overcritical operation of class C amplifiers. The collector current will
show a characteristic dip at the resonance frequency for this type of “overcritical” operation. The
depth of this dip will increase with higher values of R L .
As Figure 3-8 shows, detuning beyond the bandwidth of the matching circuit results in a significant
increase of collector current of the power amplifier and in some loss of output power. This diagram
shows the data for the circuit of the test board at the frequency of 868 MHz. The effective load
resistor of this circuit is R L = 240Ohm, which is the optimum impedance for operation at 3V. This will
lead to a dip of the collector current f approx. 20%.
Data Sheet
P
E =
R
OUT
OPT
V
~
P
S
~
O
R
I
C
OPT
V
S
Output power P o (mW) and collector efficiency E vs. load resistor R L .
45
[3 – 11]
[3 – 12]
[3 – 10]
S
=3V. A power loss in
OPT
TDA5250 D2
Version 1.7
Application
Power_E_vs_RL.wmf
and P
2007-02-26
OUT
at