EM4205-EM4305
Recommendations for Reader to Tag Timings
First Field Stop
It is recommended, but not required, that the reader sends
the first field stop while the IC is in the MOD_ON state
(modulator switch is ON). In that situation, the decay of
the oscillations across the coil inputs is faster due to the
low quality factor (modulator resistor brakes the Q factor).
The reader has to stop the field for a long enough time to
ensure oscillations on the tag coil terminals reduce from
maximum possible amplitude to an amplitude below
800mVpp when the modulator switch is OFF and
100mVpp when modulator switch is ON. Additionally, the
coil oscillations must remain below these thresholds for at
least T
MONO
time. Since the longest modulator OFF time in
default read is 40 RF periods (FDX-B, data rate 32RF and
delayed on BP/4), a first field stop of 55 RF clocks will be
detected in all cases regardless of tag Q factor.
Sending a logic "1"
For sending a logic "1", the reader field shall stay ON for
32 RF periods.
Sending a logic "0"
When sending a logic "0", the reader field shall be
stopped while the chip is in MOD_ON state.
In order to achieve reliable communication also for higher
Q factors, it is proposed to send a logic "0" by keeping the
reader field ON for 18 RF periods and switching it OFF for
14 RF periods. Increasing the field stops up to 23 RF
periods improves communication robustness.
In first phase of 18 RF periods, the IC is at the end of
MOD_OFF and starts MOD_ON. The reader field is OFF
during a complete period with the IC modulator switch ON
allowing maximum possible time to reduce amplitude of
signal on tag coil (17 RF periods of 23 are used for this
purpose). Additional 6 periods are here for the case that
amplitude on coil was reduced below 0.8Vpp just at the
end of MOD_ON state. In such a case, the field stop has
to continue for a time longer than T
MONO
to trigger the
Data Extractor output.
Figure 10 presents an example of the reader to tag
communication (read command of memory word 0) with
the timings proposed above. Quality factor of tag coil is
set to 30 and the field frequency is 125 kHz. First field
stop is done during MOD_ON state (as recommended).
The digital signal represents the field modulation input of
an electronic reader (i.e. EM4095 reader chip MOD pin).
When this input is set to a high level, the field is switched
OFF and when it is fixed to a low level, the reader chip
generates a field.
The second signal corresponds to the signal across the
EM4205/4305 coil inputs. The time base is 200us per
square.
EM4095
MOD
First
Field
Stop
Tag
Coil
inputs
“0’
’
“1’
’
“0’
’
“0’
’
“1’
’
Figure 10
MOD-OFF
MOD-ON
Copyright
2013,
EM Microelectronic-Marin SA
4205-4305-DS-01.doc, Version 4.0, 22-Oct-13
9
www.emmicroelectronic.com
EMMICRO [ EM MICROELECTRONIC - MARIN SA ]
