AN2719 Freescale Semiconductor / Motorola, AN2719 Datasheet - Page 6

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

Tango3 RF Module
Some options on the board allow different configurations to be tested:
R2 biases the output of Tango3, and C7 delivers the RF signal to the power amplifier (PA) Q1.
The base of Q1 is biased by R1, which is driven by the ENABLEPA pin. When this pin is low, the PA
current is cut. C2 bypasses the residual RF signals so that ENABLEPA is “RF cold”. L1 biases the
collector of Q1 and blocks the RF signals. C4 delivers this signal to the matching network. C1 bypasses
the power supply close to L1.
The matching network is composed of L2, L3, C8, C9, and C10. Because of its low-pass structure, it also
helps to attenuate the level of harmonic signals.
To select the proper frequency range for Tango3, the BAND pin can be connected to VCC or GND with
R6 or R7.
Computation of Values
Power Amplifier Biasing
R1 = 10 kΩ biases the base of the transistor with a 240 µA current. This current is switched when the
Tango3 RF Module is not used (ENABLEPA = 0) and during the low level of OOK modulation. This simple
biasing circuit has been tested during the evaluation of the BFR92A. When a constant 0dBm power
generator was connected to the input, the output power of the amplifier varied less than 2dB over the
6
•
•
Tango3 alone
Tango3 and power amplifier
C5
tbd
VCC
R4
tbd
R6
0
R7
0
C6
tbd
X1
tbd
R5
tbd
1
2
3
4
5
6
7
DATACLK
DATA
BAND
GND
XTAL1
XTAL0
REXT
U1
MC33493
Figure 4. Initial Schematic Diagram
ENABLE
GNDRF
RFOUT
MODE
CFSK
VCC
VCC
A Transmitter Using Tango3, Rev. 0
14
13
12
11
10
9
8
C3
tbd
R2
tbd
C11
tbd
C2
tbd
C7
tbd
R1
tbd
VCC
L1
tbd
Q1
BFR92
C1
tbd
C4
tbd
C8
tbd
L2
tbd
C9
tbd
Freescale Semiconductor
L3
tbd
C10
tbd
SMA v ert
J2