AS3953 datasheet(13/71 Pages) AMSOSRAM

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[v1-05] 2019-Feb-15

AS3953A − Detailed Description

PICC AFE

Figure 11 depicts main PICC AFE building blocks.

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

with the integrated resonant capacitor forms an LC tank with

resonance at external electromagnetic field frequency (13.56

MHz). Figure 11 depicts the main PICC AFE building blocks.

Rectifier: Extracts DC power supply from AC voltage induced

on coil terminals.

Limiter: Limits the maximum voltage on coil terminals to

protect PICC 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 PICC-to-PCD.

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 PCD.

Demodulator: Is used for communication PICC-to-PCD. It

detects AM modulation of the PCD magnetic field. The

demodulator is designed to accept modulation according to

ISO 14443A; all standard bit rates from 106 kbit/s to 848 kbit/s

are supported. The modulation for bit rate 106 kbit/s is 100%,

whereas for other bit rates it may be less.

Clock Extractor: The clock extractor extracts a digital clock

signal from the PCD carrier field frequency which is used as

clock signal by logic blocks.

HF_PON: Observes rectified regulated voltage VREC. When the

supply voltage is sufficiently high it enables operation of the

PICC AFE and the digital tag logic. A buffer capacitor and

HF_PON hysteresis guarantees that there is no reset during

reader (PCD) modulation.

Internal Regulator: Provides regulated voltage VP_INT to the

PICC AFE and in most cases also to EEPROM and logic blocks.

Typical regulated voltage VP_INT is 2.0V. A buffer capacitor is

also integrated.

External Regulator: Provides regulated voltage on external

pin VP_REG where it can be used to supply some external

circuitry. The regulated voltage and output resistance can be

adjusted using EEPROM settings (see Figure 37). Appropriate

external buffer capacitor is needed in case VP_REG is used in

the application. The current to be provided depends on reader

field strength, antenna size and Q factor, but it is limited to

maximum 5mA.

Bias: Provides bias currents and reference voltages to PICC AFE

analog blocks.

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