Freescale Semiconductor, Inc.
PLL Tuned UHF Transmitter Module
Phase-Lock Loop (PLL)
16.3 Phase-Lock Loop (PLL)
The voltage-controlled oscillator (VCO) is a completely integrated
relaxation oscillator. The frequency band of operation is selected
through the band select (BS) pin. Table 16-1 shows the PLL and
reference oscillator (XTAL) divider ratios used for each frequency band.
The exact output frequency is equal to:
XTAL frequency PLL divider ratio
Table 16-1. PLL and XTAL Divider Ratios
Band Select
Output Frequency
(MHz)
PLL Divider
Ratio
XTAL Frequency
(MHz)
868
434
315
64
32
32
13.56
13.56
9.84
The phase frequency detector and the loop filter components are
integrated in the integrated circuit (IC). An out-of-lock function is
performed by monitoring the PLL loop filter (PFD) output voltage. This
information, when exceeding limits, is used internally to disable the RF
output stage.
16.4 Frequency Band Selection
To optimize the PLL performances the 300-MHz to 950-MHz VCO
frequency range has been split into two bands centered around
315, 434, or 868 MHz and the divider ratio is set according to Table 16-1.
The BS input pin allows selection of the desired frequency band as
described in Table 16-2.
Table 16-2. Frequency Band Selection
Frequency Band
BS Pin Connected to
(MHz)
315
434
868
Open
V
/PLLEN
CC
GND
MC68HC908RFRK2
MOTOROLA
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PLL Tuned UHF Transmitter Module
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