EM4170
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
1 bit
1 bit
1 bit
16 periods
Data from EEPROM
Coded Data Measured on the COIL
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,
10
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