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
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Figure 24. Impact of duty cycle on SYNC pattern
10.15.12 Input signal envelope
The combination of the external LF antenna and any external components as shown
in Figure 25 should not significantly filter the envelope of the LF carrier as shown in
Figure 26. Excessive filtering will cause the received message error rate (MER) to
increase.
NTM88
· Antenna Q-factor acts as a 1
st
order
low-pass filter on the LF envelope
· Filter time constant: t = R.C.
· Recommended τ < 15 s
LFA
LFB
Antenna model
aaa-032036
C R
Figure 25. Antenna Q-factor equivalent model for the LF envelope
 
· Recommended τ < 15 s
· Ideal case: τ = 0 (Q-factor = 0)
· Use case: τ > 0 (Q-factor > 0)
Ï„
aaa-028026
High state part of
Manchester symbol
Low state part of
Manchester symbol
V
pp
0.63 × V
pp
Figure 26. LF envelope filtering
10.15.13 Telegram verification
The LFR has control bits to allow flexibility in the telegram format and protocol to allow
the LFR to adapt to various systems. The LFR can operate in a normal data receive
mode where it receives complete telegrams, or in a carrier detect mode where it only
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