AN2719 Freescale Semiconductor / Motorola, AN2719 Datasheet - Page 9

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

Tango3 RF Module
Figure 6. Signal Attenuation
Components Around Tango3
Starting values for C5 and C6 are the values from the data sheet: C5 = 2.2 pF, C6 = 10 pF.
X1 = 13.56 MHz will produce 433.92 MHz after a 32x multiplication with the PLL.
R4 is not used because of the low data rate. We will verify later (see “Measurements” on page 12) that it
does not lead to any spurious signals caused by modulation.
R5 = 15 kΩ; this value lowers the output power of Tango3 and reduces the supply current.
R2 = 100 Ω is a starting value.
C11 = 22 nH and C3 = 100 pF, according to the data sheet.
Optimization and Final Schematics
The Tango3 RF Module can be simply tuned, without using the MCU board, by using a low-frequency
1
generator to simulate the digital signal at 1200 bps, a power supply, and a spectrum analyzer
.
The optimization process attempts to find, for each component, a value that will lead to a better result
(maximum output power, lowest harmonic level and lowest current consumption), by testing the close
values. Once each component has been optimized during the first pass of this optimization, a second
pass is applied to finalize the work.
Increasing R2 does not lead to a major reduction in output power. 220 Ω is a good compromise between
supply current and output power.
1. We do not recommend beginning the design of a transmitter without a spectrum analyzer to analyze the frequency deviation
of the FSK modulation, the spectrum of the signal and its power.
A Transmitter Using Tango3, Rev. 0
Freescale Semiconductor
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