NXP Semiconductors
FXTH87E
FXTH87E, Family of Tire Pressure Monitor Sensors
FXTH87ERM
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Reference manual
Rev. 5.0 — 4 February 2019
119 / 183
Regarding the SYNC pattern which is non-Manchester coded, the duty cycle is applied
on all falling edges with the same proportion as a 1T Manchester symbol, as shown in
Figure 31
.
aaa-028024
Figure 31. Impact of duty-cycle on SYNC pattern
14.12 Input signal envelope
The combination of the external LF antenna and any external components as shown
in
Figure 32
should not significantly filter the envelope of the LF carrier as shown in
Figure 33
. Excessive filtering will cause the received message error rate (MER) to
increase.
FXTH87E
· 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-028025
C
R
Figure 32. 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)
τ
aaa-028026
High state part of
Manchester symbol
Low state part of
Manchester symbol
Vpp
0.63 × Vpp
Figure 33. LF envelope filtering
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