NXP Semiconductors
FXTH87E
FXTH87E, Family of Tire Pressure Monitor Sensors
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.
LFA
st
· Antenna Q-factor acts as a 1 order
low-pass filter on the LF envelope
C
R
· Filter time constant: t = R.C.
· Recommended τ < 15
s
LFB
FXTH87E
Antenna model
aaa-028025
Figure 32.ꢀAntenna Q-factor equivalent model for the LF envelope
ꢁ
· Ideal case: τ = 0 (Q-factor = 0)
V
pp
High state part of
Low state part of
Manchester symbol
Manchester symbol
· Use case: τ > 0 (Q-factor > 0)
τ
0.63 × V
pp
· Recommended τ < 15
s
aaa-028026
Figure 33.ꢀLF envelope filtering
FXTH87ERM
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Reference manual
Rev. 5.0 — 4 February 2019
119 / 183
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