S4100 MULTI-FUNCTION READER MODULE

11-06-22-715 10/2003

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13.56 MHz OPERATION

The 13.56MHz AFE transmitter consists of low impedance MOSFET with a matching network optimized to drive a

50Ω antenna resonating at 13.56MHz. The receiver section is also coupled into this network, detecting the token's

load-modulated response. The board matching network transforms the antenna’s nominal 50Ω characteristic

impedance to the proper load impedance required for the AFE. The output of the HF AFE is single-ended with one

side connected to ground. The antenna should be connected using a coaxial connection.

Depending upon the protocol used, the transmitted carrier is modulated as needed for that transponder (10% or

100% modulation), then held at full power in order to detect the load-modulated response. This response is then

demodulated, filtered, and prepared (via configurable gain and demodulation sections) for final decoding by the

microcontroller.

The HF Section of the S4100 MFR module offers a path for the development of a broad range of 13.56 MHz RFID

readers, providing the receive/transmit functions required to communicate with a variety of transponders operating

in the 13.56 MHz ISM band.

The transmitter provides a nominal 200 mW of RF power to a matched 50 ohm load.

Using a 1.5” diameter antenna and TI’s ISO 15693 compliant rectangular inlay, read ranges are typically equal to

or greater than 4”. Using the same antenna with TI’s ISO 14443 Key Fob inlay, read ranges are typically equal to

or greater than 1.5” Using larger antennas may significantly increase these read ranges.

134.2 kHz OPERATION

The 134.2kHz AFE consists of a bridge driver for carrier transmission and a high-gain receiver section for

detecting the transponder response. These sections are coupled together and designed for optimal resonance

with a 440uH coil antenna attached to the two-pin LF antenna port. Although the full bridge is protected against a

direct or resistive short to GROUND, it is designed to drive the antenna differentially. Thus, the two-port coil

antenna must be isolated from ground for proper operation.

The full bridge drives the antenna current at the 134.2kHz carrier frequency during the charge phase and the

active time of the write phase. When the full bridge is not active, the two driver outputs switch to GROUND. With

one driver port coupled to the connected antenna through the resonance capacitor, the circuit produced by the

grounded outputs allows the antenna to resonate for reception of the transponder signal (uplink).

After an initial gain stage, the received transponder uplink signal is band-pass filtered from 65kHz to 260kHz to

capture the FSK uplink nominal frequencies of 134.2kHz and 123.2kHz and reject out-of-band noise. The

received signal is then limited for decoding.

The LF antenna consists of an antenna coil connected to connector J5 pins 1 and 2. The coil inductance can vary

anywhere from 400 µH to 700 µH, with 440 µH being optimum.

Using a coil antenna approximately 2” in diameter and TI’s DST Key Fob, read ranges are typically greater than or

equal to 4 inches.