User's Manual

Table Of Contents
U
M10936
P
N7150 User Manual
UM
10936 All information provided in this document is subject to legal disclaimers.
U
ser manual
CO
MPANY PUBLIC
Rev. 2.06 November 2020
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76 of 127
2 ant
ennas. The LPCD is therefore monitoring the antenna impedance, to see if there is a
significant variation which is interpreted as being caused by a Card/Tag being in proximity.
To achieve that, the LPCD periodically generates very short pulses of RF Field, without
any modulation, and measures some antenna characteristics during this pulse. The time
between these RF pulses is defined by the TOTAL_DURATION parameter, as specified
for the RF Discovery in [NCI].
When a Card/Tag enters the field, there is an antenna impedance variation. If this variation
is higher than a pre-defined threshold, the NFC FORUM polling loop profile is automatically
started (the LPCD is not supported when using EMVCo polling loop profile). The PN7150
is then sending technology specific request commands, expecting a response since the
LPCD detected a change on the antenna impedance.
N
ote: the LPCD may also be triggered by a metal object, which can influence the Antenna
i
mpedance in a similar way as a Card/Tag. The PN7150 will anyhow detect that this object
is not a contactless device since it immediately starts sending contactless commands to
check if a Card/Tag can respond.
T
he Low Power Card Detector is configured and enabled/disabled thanks to a specific
configuration parameter TAG_DETECTOR_CFG described in →10.2.1.
The threshold is also defined by an additional configuration parameter
TAG_DETECTOR_THRESHOLD_CFG described in the same section.
The figure below describes the RF Discovery when the LPCD is enabled:
Polling phase
Listening phase
LPCD
RF pulse
F
ig 38. RF Discovery sequence in case of Low Power Card Detector mode