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Analog Front End IC TMS37122 - Reference Guide
August ’01
Figure 21:VWAKEA Sensitivity Diagram
2.10.3.2 Passive Start Sensitivity VWAKEB/1/2/3
If the system includes Passive Start function, it can be helpful to implement an indoor/outdoor
detection to avoid erroneous start of the engine by inside person in case Identification Device
is outside. For this purpose the Passive Start Wake Pattern is set to a different value than the
Passive Entry Wake Pattern. When the Passive Start Wake Pattern is received, the Identifica-
tion Device checks if the amplitude of the oscillation is above Passive Start Sensitivity
VWAKEB/1 (VWAKEB/2/3). Only if this lower threshold is exceeded, the 3D-AFE enters
the Transparent Mode and the engine can be started, because the Microcomputer can return
the correct response.
The sensitivity level for Passive Start can be adjusted depending on the system behavior. The
field strength generated outside the car by an internal Passive Start Base Station (for example:
in dashboard) must be unable under all circumstances to induce a voltage higher than the Sen-
sitivity B (see Figure 22). The threshold voltage is therefore selectable for Antenna 1 sepa-
rately by VWAKEB/1 (see Table 4 and Figure 23). For Antenna 2 and 3, which are typically
equal, a common threshold level (VWAKEB/2/3) is configurable. The range and resolution
is equal to VWAKEB/1.
0
10
20
30
40
50
60
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
CONFIGURATION
S
E
NS
IT
IV
IT
Y
[
m
V
p
p
]
SPECmin
SPECnom
SPECmax
