EM4095 RFID IC, features and specification, schematic diagram using em4095 IC

The antenna 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 sine wave.

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 Tags.

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 data stream.

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:

·	Integrated PLL system to achieve self adaptive carrier frequency to antenna resonant frequency.

·	100 to 150 kHz carrier frequency range.

·	Direct antenna driving using bridge drivers.

·	Data transmission by OOK (100% Amplitude Modulation) using bridge driver