AN2719 Freescale Semiconductor / Motorola, AN2719 Datasheet - Page 7

• Manufacturer Part Number: AN2719
• Description: A Transmitter Using Tango3 (Step-by-step Design for ISM Bands)
• Manufacturer: Freescale Semiconductor / Motorola

voltage range (1.9V to 3.6V) and over a large temperature range (-20°C to +60°C). The difference of
behavior compared to a more complex voltage-regulated bias using diodes was too little to justify an
increase in complexity (less than 1dB improvement over voltage range).
C2 = 100 pF presents a low impedance at 433 MHz compared to R1 and avoids having RF voltages on
the ENABLEPA line.
C1 = 100 pF is the decoupling capacitor for the load of Q1.
The RF signal is applied to the base of Q1 with C7 = 4.7 nF (low impedance at 434 MHz compared to the
input impedance of Q1).
Optimum Load Impedance
To achieve maximum efficiency of the power amplifier, it should work in C-class. In this case, the optimum
value of the load of Q1 can be found from the following equation.
where...
Vcc = voltage of the power supply
Vsat = saturation voltage
Pout = wanted output power
Assuming:
Matching Network
A matching network has been defined to match RLoad to 50 Ω. Simple Smith chart software can be used
to design this network, thereby avoiding extensive computation.
Freescale Semiconductor
RLoad
RLoad
•
•
•
Output power = +13 dBm or 20mW
Vcc = 3V
Vsat = 1V
=
=
(
---------------------------------
(
------------------ -
2
Vcc Vsat
3 1
2
×
–
×
0.2
–
Pout
)
2
=
)
100Ω
2
A Transmitter Using Tango3, Rev. 0
Tango3 RF Module
7