tda5251f1 Infineon Technologies Corporation, tda5251f1 Datasheet - Page 43

• Manufacturer Part Number: tda5251f1
• Description: Ask/fsk 315mhz Wireless Transceiver
• Manufacturer: Infineon Technologies Corporation

Confidential
The output power P o will be reduced when operating in an “overcritical” mode at a R
shown in Figure 3-7, however, power efficiency E (and bandwidth) will increase by some degree
when operating at higher R L . The collector efficiency E is defined as
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 .
Preliminary Specification
E
P
R
OUT
=
OPT
V
~
S
~
P
R
0
OPT
I
V
C
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_315.wmf
TDA5251 F1
Version 1.0
Application
and P
L
2003-02-18
> R
OUT
LC
. As
at