NXP Semiconductors
UM11227
NTM88 family of tire pressure monitor sensors
UM11227 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2020. All rights reserved.
User manual Rev. 6 — 24 April 2020
82 / 205
10.15 Low frequency (LF) receiver module
The low-frequency receiver (LFR) is a very low-power, low-frequency, receiver system for
short-range communication in TPMS. The module allows an external coil to be connected
to two dedicated differential input pins. In TPMS systems a single coil may be oriented
for optimal coupling between the receiver in the tire or wheel and a transmitter coil on the
vehicle body or chassis.
This LFR system minimizes power consumption by allowing flexibility in choosing
the ratio of on to off times and by turning off power to blocks of circuitry until they are
needed during signal reception and protocol recognition. In addition, this LFR system
can autonomously listen for valid LF signals, check for protocol and ID information so the
main MCU can remain in a very low power standby mode until valid message data has
been received.
The LFR can be configured for various message protocols and telegrams to allow it to
be used in a broad range of applications. The message preamble must be a series of
Manchester coded bits at the nominal 3.906 kbit/s data rate. A synchronization pattern
is used to mark the boundary between the preamble and the beginning of Manchester
encoded information in the message body. The synchronization pattern is a non-
Manchester specific TPMS pattern. Messages can optionally include none, an 8-bit or
a 16- bit ID value. Messages may contain any number of data bytes with the end-of-
message indicated by detecting an illegal Manchester bit at a data byte boundary.
It is not intended that LFR may be actively receiving/decoding LF signals while physical
parameter measurements are being made; or during the time that the RFM may be
actively powered up and/or transmitting RF data. The resulting interactions will degrade
the accuracy of the LF detection.
AMP1
LFA
LFB
BUFF1 AMP2
DATA SLICER
BUFF2 AMP3 BUFF3
Vref_sensitivity
aaa-028019
SENSITIVITY
CARRIER
DETECTOR
CLAMP
R
V
RECTIFIER0 RECTIFIER1 RECTIFIER2
SUMMATOR AVERAGE
FILTER
RECTIFIER3
LOGIC BLOCK 2
· DATA DECODING
129 kHz
typ
1 kHz_clock typ
LOGIC BLOCK 1
· ON/OFF CYCLING
· CARRIER DETECTION
Figure 19. Block diagram
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