Application Note: FAQ about EM4095 R/W

AppNote 403
Application Note 403
Frequently Asked Questions about EM4095
Analog Front End 125 KHz RFID Base Station
Product Family:
Part Number:
FAQ, Analog Front End, RFID, 125 kHz
25 September 2002
Question: How can I send data from the base station
to the RFID transponder?
as it is given by the wire manufacturer (±10%). My
question is what is the acceptable resistance
tolerance in the wire in order to maintain ±1%
induction tolerance as recommended by EM?
Answer: The pin MOD of the EM4095 is used to modulate
the 125 kHz RF field. In effect, when you apply a:
High level on this pin, you'll block the antenna drivers
and switch the electromagnetic field off.
Low level on MOD will put the on-chip VCO in a free
running mode and you'll have a 125 kHz carrier
without modulation on your antenna. More
explanations can be found on page 6 of the EM4095
Question: During my project development with
EM4095, some questions have been raised regarding
the "EM4095 calculation spreadsheet":
1. What does the value Rant_r, stand for? (Antenna +
IC's resistance - Rad (3-9Ω) +...?)
Answer: The term Rant means the serial resistor of
your antenna. You can calculate it by using the quality
factor Q, Q = (2 * π * F0 * Lant) / Rant_r.
2. What does Rser exactly stand for in the
Answer: Rser is the resistance that you connect in
serial mode with your antenna. This resistance limits
high voltage by reducing the overall quality factor. At
the same time, it limits the driver's current.
3. What are the recommended maximum voltage
values across the antenna and on the DEMOD_IN
Answer: The maximum voltage across the antenna
depends on the antenna current. We recommended a
maximum current of 250mA on the output drivers.
The input voltage at DEMOD_IN has to be limited by a
capacitor divider. This signal has to meet the EM4095
common range specifications (min= Vss+0.5 & max=
Answer: The resistance tolerance should not be a
major issue regarding the inductance tolerance of the
inductor: The resistive tolerance will only affect the
tolerance of the Q factor, but should not interfere on
the L value. If the coil supplier can guarantee the
number of turns and the wire section you should be
close enough the requested inductance tolerance.
5. In the EM4102 datasheet, Manchester code "1" is
represented with "01" and code "0" is represented
with "10". In our tests, we found that it is exactly
the opposite. Are we missing some information?
Answer: For more information, please refer to
application note 411 "RFID Made Easy" .
Question: The Q factor has been calculated as
where Fo=125Khz, Lr=410uH, Rl=9Ω (Given from the
coil resistance). In the application note, coil with air
core usually has Q=15; however, our design, which
also has an air coil, the Q factor is calculated at 34.9.
Is this ok, given that EM's recommendation is to take
Q value as high as possible?
Answer: A quality factor of 35 should give you improved
detection distance, while affecting the data transfer rate.
The recovery time to switch from one state to another is
higher due to the increased time to dampen the
4. I talked with a company that manufactures
antennae and asked them whether they can
produce an antenna with ±1% induction tolerance.
They can only assure the wire resistance tolerance
Copyright  2002, EM Microelectronic-Marin SA
AppNote 403
Question: I’m using the EM4095 demoboard. How do I
have to initialise the system in Write mode?
(Bitmuster, Timing). With which data rate can EM4150
Transponders be programmed?
Answer: The data rate of the EM4150 RFID transponder
depends on the chip version that you have selected.
Please refer to the last page of the corresponding data
Concerning your write mode problems, it could be due to
one of the following causes:
The transponder's main supply. In effect, notice in
EM4150 datasheet (Page 3), that the supply
current/write is 15 times bigger than the supply
current/read. It means that the reading distance is
always bigger than the write distance. One solution will
be to reduce the distance between transponder and
A chip write protection. If you lock a part or the
complete EEPROM area, your chip will protect all its
data. For more information you could refer to the
EM4150 datasheet, fig.6
To write on a chip's memory, you've to wait for a LIW
(Listen Window). At this moment your transceiver must
send the RM pattern and the write command. If you
send your command without waiting for a LIW, the
transponder won't understand the command. In write
mode, you don't need to initialize anything. The chip
initialization is made just after the chip's Power On
Question: Our customer is using the EM4095 reader
demoboard and needs the specification of the serial
protocol (Start/stop bit etc.) to interface a
microcontroller. Is an encrypted protocol version of
the EM4095 in the roadmap? Our customer would like
to copy the EM4095 reader demoboard layout for its
application. Which program was used (eg. Orcad.
Eagle) to create the layout file?
Answer: Concerning your first question, the serial protocol
sent by the microcontroller depends on the transponder
that the customer is using. Each transponder has its own
Regarding data synchronization, please use the RDY/CLK
The layout file of the EM4095 reader demoboard is a
standard Gerber file format. Any software able to read this
format can be used to process the file (i. e. Orcad).
EM Microelectronic-Marin SA cannot assume responsibility for use of any circuitry described other than circuitry
entirely embodied in an EM Microelectronic-Marin SA product. EM Microelectronic-Marin SA reserves the right to
change the circuitry and specifications without notice at any time. You are strongly urged to ensure that the
information given has not been superseded by a more up-to-date version.
© EM Microelectronic-Marin SA, 09/2002, Rev. C
Copyright  2002, EM Microelectronic-Marin SA