Electronics Design and Manufacture
ABN: 57 995 688 558
by ATMEL, the U2270B IC forms the RF front end of a
Read/Write RFID base station. Used in 125kHz RFID systems it can be
used in such applications as access control, immobilizer systems,
process control and general Contactless ID systems.
The U2270B features:
You can buy U2270B IC's direct from our online shopfront.For a general overview of RFID systems. See RFID basics
The U2207B has various operating modes. In this example a 12V supply allows for greater reading range.
has an on board rectifier which simplifies the generation of a external
supply for a digital
processor (Vext ~ 4.6-6.3V).
The antenna coil inductance L and capacitor Cres is a tuned circuit set to resonate at 125kHz. This resonant
frequency can be derived by using the formula:
Once the circuit parameters L and Cres are derived the frequency of the on chip oscillator can be set. The
U2207B has an on chip oscillator which drives the antenna coil. This frequency is selected by a fixed resistor
between the pins Vs, and RF. In the example above this resistance is the sum of R1 and R2, giving us a
resistance value of 110 ohms.
In operation the antenna coil generates an electromagnetic field at 125kHz. When a Transponder enters this
field it draws power from it, and when sufficient power is available it starts to transmit its data by modulating
the RF field. The modulated field is sensed by the U2270B at the INPUT pin. The raw demodulated data
generated by the action of the transponder is then made available at the OUTPUT pin for the digital processor
to decode. The demodulated data appearing at the OUTPUT pin can be encoded in various protocols
depending on the type of RFID transponder that is being used. For a description of Read Only transponders
utilizing EM4100 protocol see EM100 protocol.
In addition to the OUTPUT pin the digital processor can control the CFE input pin of the U2270B to allow
data transfer from reader to transponder. When CFE is set low the RF field is turned off. By turning the
RF field on and off in a predefined manner data can be sent to the transponder. This is required when writing
data to a transponder capable of READ/WRITE or cryptographic functionality.
To assist in your own RFID system design we also stock: