P4022 EM Microelectronic, P4022 Datasheet - Page 10

• Manufacturer Part Number: P4022
• Description: Multi Frequency Contactless Identification Device
• Manufacturer: EM Microelectronic

time between when the last code bit is transmitted
and when the GAPs are expected. One reason for
the drift is that the oscillator is supply voltage
dependent, and the supply voltage will typically
be rising during this time, since the transponder
will not be modulating its coil or antenna.
The slope of the rising and falling edges of the
GAPs can also be adjusted to reduce reader
power bandwidth. In the case of high frequency
GAPs the envelope is used directly.
frequency GAPs have to be pre-processed. They
are detected by checking for high periods lasting
longer than one bit period. For this reason there is
a set-up time of 1 bit. The minimum GAP width is
therefore 1 bit period (T
MUTE
The MUTE signal is received asynchronously by
the transponder. The controller checks for a HIGH
less than 7 bits wide after pre-processing (T
timing diagram). As in the case of the ACK, low
EM MICROELECTRONIC-MARIN SA
Figure 6: MUTE and WAKE-UP timing diagrams
1
in the timing diagram).
2
in the
Low
frequency MUTE GAPs must be at least one bit
wide, but high frequency GAPs can be arbitrarily
narrow.
When transmitting a MUTE, the reader must take
into account that there could be a spread of 30%
in the clock frequencies of all the receiving
transponders. The reader should therefor limit the
width of a MUTE to be less than 5 bits of the
nominal bit rate (T
frequency MUTE should also be wider than 1.5
bits of the nominal bit rate (T
diagram).
The MUTE should be sent as early as possible
after a code transmission has been detected,
while
transmission and not just noise. The earlier the
MUTE is sent, the more time the reader has to
recover before the SYNCH and code bits arrive,
and the smaller the probability that another
transponder has started a colliding transmission.
still making sure that it
4
in the timing diagram). A low
P4022
PRELIMINARY
3
in the timing
is
a
code
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