AN2719 Freescale Semiconductor / Motorola, AN2719 Datasheet - Page 4

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

RF Module Specifications
C5 and C6 modify slightly the resonance frequency of the crystal oscillator. An internal switch on pin
CFSK can short circuit C5 and thus allow frequency modulation. This kind of modulation is called “crystal
polling”. R4 prevents spurious signals from occurring at high modulation frequencies.
The RF signal is available on pin RFOUT; the resistor connected to REXT controls its level. The output
stage is a single ended RF current source, biased by the loop antenna.
The loop antenna is tuned by C12; its selectivity prevents radiation of harmonic signals.
C3 and C11 decouple the power supply (3V), to prevent parasitic oscillation of the circuit.
This transmitter can easily be driven by a microcontroller.
The software should first set BAND and MODE, according to the target frequency and type of modulation
chosen (these signals can also be wired directly to ground or VCC), and then set ENABLE high, before
sending data on the DATA pin.
The signal available on the DATACLK pin can be used by the microcontroller for its internal timing. Thus,
the microcontroller does not require an accurate internal clock to achieve accurate timing.
This simple design has the following advantages.
However, it does have the following drawback.
The proposed design should not suffer this drawback and should have increased radiated power.
RF Module Specifications
Overview
The Tango3 RF Module is part of a project to make a transmitter for long-range remote control.
1. This feature is fully exploited with the MC68HC908RF2 chip that includes both Tango3 and an HC08 MCU specially designed
to use this signal.
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Cost effective
Compact
Low power consumption
Tuning is not affected by touching the antenna
Poor radiated level: loop antennas are not efficient, and the output power is not the maximum
allowed by ETSI regulations EN300-220.
A Transmitter Using Tango3, Rev. 0
Freescale Semiconductor
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