ST25R3910 datasheet(8/65 Pages) STMICROELECTRONICS

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Functional overview

ST25R3910

8/65

DocID029768 Rev 2

The ST25R3910 transmitter is intended to directly drive antennas (without 50 Ω cable,

usually antenna is on the same PCB). Operation with 50 Ω cable is also possible, but in that

case some of the advanced features are not available.

1.1.2

Receiver

The receiver detects tag modulation superimposed on the 13.56 MHz carrier signal. The

receiver contains two receive chains (one for AM and another for PM demodulation)

composed of a peak detector followed by two gain and filtering stages and a final digitizer

stage. The filter characteristics are adjusted to optimize performance for each mode and bit

rate (sub-carrier frequencies from 212 kHz to 848 kHz are supported). The receiver chain

inputs are the RFI1 and RFI2 pins. The receiver chain incorporates several features that

enable reliable operation in challenging phase and noise conditions.

1.1.3

Phase and amplitude detector

The phase detector is observing the phase difference between the transmitter output signals

(RFO1 and RFO2) and the receiver input signals (RFI1 and RFI2). The amplitude detector is

observing the amplitude of the receiver input signals (RFI1 and RFI2) via self-mixing. The

amplitude of the receiver input signals (RFI1 and RFI2) is directly proportional to the

amplitude of the antenna LC tank signal.

The phase detector and the amplitude detector can be used for the following purposes:

•

PM demodulation, by observing RFI1 and RFI2 phase variation

•

Average phase difference between RFOx pins and RFIx pins is used to check and

optimize antenna tuning and inductive wakeup via the MCU

•

Amplitude of signal present on RFI1 and RFI2 pins is used to check and optimize

antenna tuning

1.1.4

A/D converter

The ST25R3910 contains a built in Analog to Digital (A/D) converter. Its input can be

multiplexed from different sources and is used in several applications (measurement of RF

amplitude and phase, calibration of modulation depth…). The result of the A/D conversion is

stored in a register and can be read via SPI.

1.1.5

External field detector

The External field detector is a low power block switched on in NFCIP target mode to detect

the presence of the initiator field, and also used during the NFCIP Collision Avoidance

procedure.

1.1.6

Quartz crystal oscillator

The quartz crystal oscillator can operate with 13.56 MHz and 27.12 MHz crystals. At start-up

the transconductance of the oscillator is increased to achieve a fast start-up. The start-up

time varies with crystal type, temperature and other parameters, hence the oscillator

amplitude is observed and an interrupt is sent when stable oscillator operation is reached.

The oscillator block also provides a clock signal to the external microcontroller (MCU_CLK),

according to the settings in the control register.

ST25R3910 Datasheet(PDF) 8 Page - STMicroelectronics

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