AN1833 Freescale Semiconductor / Motorola, AN1833 Datasheet - Page 17

• Manufacturer Part Number: AN1833
• Description: A Low-Power Wireless Remote Control Transmitter and Receiver
• Manufacturer: Freescale Semiconductor / Motorola

Low-Power
Transmitter
AN1833
MOTOROLA
The schematic in
It is comprised of the MC13176 UHF PLL transmitter, the
MC68HC705J1A MCU, and the reference/tripler.
The PLL reference at pin 9 is derived from tripling the 4-MHz crystal
reference from the MCU. In this tripler, a low-cost transistor,
MMBT3904L [8], is used with a 7-mm shielded transformer that provides
the 12-MHz resonant LC tank at the output of the transistor and also the
means to easily supply dc to the collector output. The transformer is a
part supplied by Toko America [9] (part number 600GCS-8519N).
Twelve MHz, the third harmonic from the 4-MHz crystal, is selected by
the LC resonant circuit formed by the primary windings between pins
1 and 2 of the transformer and an external capacitor of 330 pF.
The secondary output of the transformer uses a tapped capacitor
transformer to provide a lower source impedance to the reference input
of the MC13176 (pin 9) while forming a second LC resonant network.
Thus, the tripler circuit is a double tuned LC network which provides
increased selectivity of the 12-MHz signal.
Freescale Semiconductor, Inc.
For More Information On This Product,
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Figure 5. RSSI Output Rise and Fall Times
0
Figure 6
versus RF Input Signal Level
– 20
shows the handheld OOK transmitter circuit.
RF INPUT SIGNAL LEVEL (dBm)
– 40
Automatic Frequency Control
– 60
Application Note
t
t
t
t
t
t
r
f
r
f
r
f
@ 22 k
@ 47 k
@ 100 k
@ 22 k
@ 47 k
@ 100 k
– 80
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