TDA5250D2 Datasheet, PDF (46/97 Pages) Infineon Technologies AG – ASK/FSK 868MHz Wireless Transceiver

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TDA 5250 D2
preliminary
Applications
The LNA-matching is RF-grounded now, so no power is lost in the LNA-input.
The PA-matching consists of C2, C3 L2, C4 and L1.
When designing the matching of the PA, C2 must not be changed anymore
because its value is already fixed to the LNA-input-matching.
4.1.2 Power-Amplifier
The power amplifier operates in a high efficient class C mode. This mode is
characterized by a pulsed operation of the power amplifier transistor at a current
flow angle of θ<<π. A frequency selective network at the amplifier output
passes the fundamental frequency component of the pulse spectrum of the
collector current to the load. The load and its resonance transformation to the
collector of the power amplifier can be generalized by the equivalent circuit of
Figure 4-6. The tank circuit L//C//RL in parallel to the output impedance of the
transistor should be in resonance at the operating frequency of the transmitter.
V_S
LC
R_L
Figure 4-6 Equivalent power amplifier tank circuit
Equivalent_power_wmf.
The optimum load at the collector of the power amplifier for “critical” operation
under idealized conditions at resonance is:
R_LC
=
V_S ²
2P_O
[4 – 8]
A typical value of R_LC for an RF output power of P_o= 13mW is:
RLC
=
3²
2 ∗ 0.013
=
350Ω
[4 – 9]
Wireless Components
4-6
Specification, July 2002