tda5255e1 Infineon Technologies Corporation, tda5255e1 Datasheet - Page 43

• Manufacturer Part Number: tda5255e1
• Description: Ask/fsk 434mhz Wireless Transceiver
• Manufacturer: Infineon Technologies Corporation

Confidential
The diagram of Figure 3-7 has been measured directly at the PA-output at V
the matching circuit of about 3dB will decrease the output power. As shown in the diagram, 250
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 434MHz. The effective load
resistor of this circuit is R L = 250Ohm, which is the optimum impedance for operation at 3V. This will
lead to a dip of the collector current f approx. 20%.
Preliminary Specification
P
E
R
OUT
OPT
V
~
P
S
~
R
O
I
C
OPT
V
S
Output power P o (mW) and collector efficiency E vs. load resistor R L .
43
[3 – 11]
[3 – 12]
[3 – 10]
S
=3V. A power loss in
OPT
Power_E_vs_RL_434.wmf
TDA5255 E1
Version 1.1
Application
and P
2002-11-28
OUT
at