EM4170

Copyright

 2002, EM Microelectronic-Marin SA

10

www.emmicroelectronic.com

Power On Reset

When the EM4170 with its attached coil will enter an electromagnetic field, the built in AC/DC converter will supply the chip.

The DC voltage is monitored and a Reset signal is generated to initialise the logic. The power On Reset is also provided in

order to make sure that the chip will start issuing LIWs and be ready to accept commands with a sufficient DC power level.

An hysteresis is provided to avoid improper operation at limit level.

AC/DC Converter and Voltage Limiter

The AC/DC converter is fully integrated on chip and will extract the power from the incident RF field. The internal DC

voltage will be clamped to avoid high internal DC voltage in strong RF fields.

DC Output

V

AC Input

Fig. 14

Clock Extractor

The Clock extractor will generate a system clock with a frequency corresponding to the frequency of the RF field. The

system clock is fed into a sequencer to generate all internal timings.

The clock extractor is optimised for power-consumption, sensitivity and noise-suppression. As the input signal is subject to

a large dynamic range due to the amplitude modulation, the clock-extractor may miss clocks or add spurious clocks close

to the edges of the RF-envelope. This de-synchronisation will not be larger than ± 1 clocks per Bit and must be taken into

account when developing reader software.

Data Extractor

The transceiver-generated field will be amplitude modulated to transmit data to the EM4170. The Data extractor

demodulates the incoming signal to generate logic levels, and decodes the incoming data.

Modulator

The Data Modulator is driven by the serial data outputted from the memory or the Crypto-Logic which is Manchester

encoded. The modulator will draw a large current from both coil terminals, thus amplitude modulating the RF field

according to the memory data.

Communication from Transponder to the Transceiver (READ MODE)

The EM4170 modulates the amplitude of the RF field to transmit data to the transceiver. The data is output serially from the

EEPROM and Manchester encoded.

1 bit

32 periods of

RF field

Coded Data Measured on the COIL

Data from EEPROM

16 periods

1 bit

1 bit

1 bit

Fig. 15

The EM4170 uses different patterns to send status information to the transceiver. Their structure cannot be confused with

a bit pattern sequence. These patterns are the Listen Window (LIW) to inform the transceiver that data can be accepted,