ST25R3920B datasheet(17/158 Pages) STMICROELECTRONICS

17 / 158 page

DS13890 Rev 4

17/158

ST25R3920B

Description

157

2.2.7

Quartz crystal oscillator

The quartz crystal oscillator operates with 27.12 MHz crystals. At start-up the

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

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

observed and an interrupt is generated 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 IO configuration register 1.

2.2.8

Power supply regulators

The integrated power supply regulators ensures a high power supply rejection ratio (PSRR)

for the complete system.

Three voltage regulators, one for the analog block, one for the digital block, and one for the

RF output drivers, are available to decouple noise sources from the ST25R3920B. A fourth

voltage regulator generates the reference voltage for the analog receivers (AGDC, analog

ground).

The RF output driver voltage regulator is configured automatically by the ST25R3920B

based on the systems power supply stability and RF output power (see Section 4.4.10:

Adjust regulators for more details).

2.2.9

POR and bias

This block provides bias currents and reference voltages to all other blocks. It also

incorporates a Power on Reset (POR) circuit that provides a reset at power-up and at low

supply levels.

2.2.10

RC oscillator and Wake-up timer

The ST25R3920B includes several possibilities for low power detection of a card presence

(phase measurement, amplitude measurement). The RC oscillator and the register

configurable Wake-up timer are used to periodically trigger the card presence detection in

the low power card detection modes.

2.2.11

TX encoding

This block encodes the transmit frames according to the selected RF mode and bit rate. The

SOF (start of frame), EOF (end of frame), CRC and parity bits are generated automatically.

The data to transmit are taken from the FIFO.

In Stream mode the framing is bypassed. The FIFO data directly defines the modulation

data sent to the transmitter.

In Transparent mode, the framing and FIFO are bypassed, and the MOSI pin directly drives

the modulation of the transmitter.

2.2.12

RX decoding

This block decodes received frames according to the selected RF mode and bitrate. The

received data is written to the FIFO.

In Stream mode the framing is bypassed. The digitized subcarrier signal is directly stored in

the FIFO.

ST25R3920B Datasheet(PDF) 17 Page - STMicroelectronics

ST25R3920B Datasheet(HTML) 17 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL