www.ams.com

Revision 1.0

9 - 42

AS3953

Datasheet - D e t a il e d D es c r i pt io n

7 Detailed Description

Figure 3. System Block Diagram

7.1 Circuit

The AS3953 is composed of ISO 14443A PICC Analog Front-end (PICC AFE), the ISO 14443A PICC Logic (PICC Logic), EEPROM, SPI

Interface, Level Shifters and Power Supply Manager Block (Power Manager).

The PICC AFE is connected to an external tag coil, which forms together with integrated resonant capacitor an LC tank with a resonance at the

external electromagnetic field frequency of 13.56 MHz. The PICC AFE has a built in rectifier and regulators. Output of internal regulator is called

VP_INT. It is used to supply the PICC AFE and usually also the LOGIC and EEPROM (through Power Supply Manager). Output of external

regulator VP_REG is available on a pin to supply some external circuitry.

Power Manager is controlling power supply of Logic and EEPROM. The two blocks can be supplied either from VP_INT or from VP_SPI (SPI

power supply). In order to save current on VP_SPI, VP_INT is used as power supply whenever it is available. VP_SPI is only used when some

activity is started over the SPI and the VP_REG is too low to be used as a power supply.

The PICC Logic is responsible for PICC-to-PCD communication up to the Level-4 (block transmission) of ISO 14443A. This means that anti-

collision and other low-level functionality are implemented there.

The SPI Interface logic contains a 32 byte FIFO for block transmission data which is exchanged on Level-4 of ISO 14443A communication. It

also contains some control and display registers.

The EEPROM is used to store the UID, the housekeeping data (configuration and control bits) and user data. It can be accessed from both sides

(RFID and SPI).

7.2 PICC AFE

Figure 4 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 4 depicts the main PICC AFE building blocks.

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

called load modulation. Variation of current in the modulator switch (ON and OFF state) is seen as modulation by the PCD.

accept modulation according to ISO 14443A; all standard bit rates from 106 kb/s to 848 kb/s are supported. The modulation for bit rate 106 kb/s

is 100%, whereas for other bit rates it may be less.

ISO 14443A

Reader

AS3953

Microcontroller

SPI