FXTH870xD
Sensors
Freescale Semiconductor, Inc.
111
13
RF Module
It is not intended that the RFM may be actively powered up and/or transmitting RF data while physical parameter measurements
are being made; or during the time that the LFR may be actively receiving/decoding LF signals. The resulting interactions will
degrade the performance of the RF output spectrum.
The FXTH870xD consists of an RF module (RFM) with external crystal-driven oscillator, VCO, fractal-n PLL and RF output
amplifier (PA) for an antenna. It also contains a small state machine controller, random time generator and hardware data buffer
for automated output or direct control from the MCU. The overall block diagram is shown in
Figure 89
.
Figure 89. RF Transmitter Block Diagram
13.1
RF Data Modes
There are two modes of operation in using the RF output in either the data buffer mode or MCU direct mode.
13.1.1
RF Data Buffer Mode
In the RF data buffer mode the transmissions are sent by dedicated logic hardware while the MCU can be put into a low power
mode until the transmission is completed. This RF state machine is clocked by the MFO which is enabled when the SEND bit is
set and when any of the LFR, SMI or MCU are operating.
The RF data buffer consists of a dedicated RFM state machine and a 256-bit data buffer. The RF data buffer is loaded with
whatever data pattern the user software creates. The number of data bits to be sent is selected by the FRM[7:0] control bits. The
control logic is triggered by the SEND control bit when it is time to transmit the data which is sent to the RF stage after being
encoded as either Manchester, Bi-Phase or NRZ data according to the method selected by the CODE[1:0] bits as described in
.
Before the data can be transmitted the RFM control logic enables the external crystal oscillator and phase-locked-loop to initialize
before the RF output stage can begin transmission.
CRYSTAL
CONTROL
REGISTERS
RF
AMP
VCO
XI
XO
PHASE
DETECTOR
RF
LOW-PASS
FILTER
FRACTIONAL-N
DIVIDER
OSCILLATOR
AND LOGIC
256-BIT
DATA BUFFER
MODULATION
CONTROL
RF
STATE
MACHINE
MCU
AV
DD
AV
SS
V
REG
RINT
LFSR
RANDOM
GEN
MFO
D
X
500 kHz
VOLT
REG
RF
AV
DD
RF
LVD
Содержание FXTH870 D Series
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