Electronics Design and Manufacture
ABN: 57 995 688 558
by EM Microelectronic, the EM4095 is a Read/Write
analog front end for a 125kHz RFID base station. With only a few
external components the EM4095 can generate the 125kHz resonant
magnetic field required for reading and writing of magnetically coupled
RFID Transponders. See RFID basics for a general overview of RFID
The EM4095 features:
You can buy EM4095 IC's direct from our online shopfront.
Shown here is a typical configuration for reading and writing a 125kHz Tag.
coil inductance L and capacitor Cres is a tuned circuit set to resonate
at 125kHz. Transponder
Tags have similarly tuned antenna circuits so as to maximize the power and signal transfer between the two.
The EM4095 will drive the antenna at its resonant frequency using its internal driver circuit. This is a simple
When a Read Only Transponder enters the Electromagnetic field it draws power from it, and when sufficient
power is available it starts to transmit its data by modulating the RF field. This modulated signal is sensed at
the Demod_In Input of the EM4095. As the coil is being driven at its resonant frequency the voltage at the
junction of L and Cdv1 can be quite high. Typically of the order of 30V to 100V peak to peak, depending on
the quality of the coil. Since the maximum permitted voltage on the Demod_in pin is only 5V a simple voltage
divider circuit is introduced by including Cdv1, and Cdv2. The expected voltage on the antenna coil should
be calculated first in order to determine the correct ratio of Cdv1, and Cdv2 to give the required division ratio.
The Interface to the EM4095 is through 4 lines. These are Rdy/Clk, Mod, SHD, and Dmod_out.
The SHD pin controls the sleep mode of the device. When SHD is set to high the EM4095 is placed in sleep
mode and current is minimized. For normal operation SHD is set Low.
The Mod input selects between Read and Write operations. For Read only transponders such as used with
EM4100 compatible Tags this pin is set Low. See EM100 protocol to learn more about EM4100 compatible
The Rdy/Clk output provides a clock signal synchronized to the signal at ANT1. This is used by the digital
processor to help decode the incoming bit data stream.
The Demod_out output contains the demodulated output of the signal detected on the Demod_in pin.
Typically this is not the actual bit data present within the Transponder. Often the bit data stream is encoded
using various schemes to allow both data and clock to be embedded within the signal. The digital processor
will use both the data from the Dmod_out line and the system clock from the Rdy/Clk line to fully decode the
To complete your RFID reader design your digital processor will need to be a suitably fast microprocessor or
other computing device in order to translate the encoded data that streams from the EM4095 device, and to
format the data in a more useful form. Further to that the digital processor can then take appropriate actions
based on the data stored on the Transponder. In this way systems such as used in Access Control, animal
tracking, or general inventory control can be designed. To assist in your own RFID system design we also stock: