PLL Tuned UHF Transmitter Module
Transmitter Functional Description
MC68HC908QF4 — Rev. 1.0
Data Sheet
MOTOROLA
PLL Tuned UHF Transmitter Module
103
12.2 Transmitter Functional Description
The transmitter is a phase-locked loop (PLL) tuned low-power UHF transmitter.
The different modes of operation are controlled by the microcontroller through
several digital input pins. The power supply voltage ranges from 1.9 V to 3.6 V
allowing operation with a single lithium cell.
12.3 Phase-Lock Loop (PLL) and Local Oscillator
The VCO is a completely integrated relaxation oscillator. The phase frequency
detector (PFD) and the loop filter are fully integrated.The exact output frequency is
equal to:
fRFOUT = fXTAL x PLL divider ratio
The frequency band of operation is selected through the BAND pin. Table 12-1 provides details for each frequency band selection.
An out-of-lock function is performed by monitoring the internal PFD output voltage.
When it exceeds its limits, the RF output stage is disabled.
12.4 RF Output Stage
The output stage is a single-ended square wave switched current source.
Harmonics will be present in the output current drive. Their radiated absolute level
depends on the antenna characteristics and output power. Typical application
demonstrates compliance to European Telecommunications Standards Institute
(ETSI) standard. A resistor REXT connected to the REXT pin controls the output
power allowing a tradeoff between radiated power and current consumption. The
output voltage is internally clamped to:
VCC ± 2 VBE (typically VCC ±1.5 V @ TA = 25°C).
Table 12-1. Frequency Band Selection
and Associated Divider Ratios
BAND Input
Level
Frequency
Band (MHz)
PLL Divider
Ratio
Crystal Oscillator
Frequency (MHz)
High
315
32
9.84
434
13.56
Low
868
64
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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