AS3955 datasheet(12/111 Pages) AMSCO

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[v1-01] 2015-Apr-29

AS3955 − Detailed Description

Analog Frontend (AFE)

The AFE is connected to external tag coil, which together with

the integrated resonant capacitor forms an LC tank resonating

at the external electromagnetic field frequency (13.56 MHz).

Figure 13 depicts the main AFE building blocks.

Figure 13:

PICC AFE Block Diagram

Rectifier extracts DC power supply from the AC voltage

induced on coil terminals.

Limiter limits the maximum voltage on coil terminals to protect

AFE from destruction. At voltages that exceed limiter voltage it

starts to absorb current (acts as some sort of shunt regulator).

Modulator Switch is used for communication the NFC tag to a

NFC device. When switched on it will draw current from coil

terminals. This mechanism is called load modulation. Variation

of current in the modulator switch (ON and OFF state) is seen

as modulation by the NFC device.

Detailed Description

PON

RECTIFIER

MODULATOR

SWITCH

LIMITER

DEMODULATOR

CLOCK

EXTRACTOR

LC1

LC2

NFC Type 2

Tag Logic

EXTERNAL

REGULATOR

BIAS

VP_REG

INTERNAL

REGULATOR

VP_INT

VREC

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