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| TDA5250D2 Datasheet, PDF (48/97 Pages) Infineon Technologies AG – ASK/FSK 868MHz Wireless Transceiver | |||
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confidential
TDA 5250 D2
preliminary
Applications
Figure 4-7
Power_E_vs_RL.wmf
Output power Po (mW) and collector efficiency E vs. load resistor RL.
The DC collector current Ic of the power amplifier and the RF output power Po
vary with the load resistor RL. 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 âovercriticalâ operation. The depth of this dip will
increase with higher values of RL.
As Figure 4-8 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 RL= 240Ohm, which is the optimum impedance for operation at 3V. This will
lead to a dip of the collector current of approx. 20%.
Figure 4-8 Power output and collector current vs. frequency
pout_vs_frequ.wmf
Wireless Components
4-8
Specification, July 2002
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