STMicroelectronicsS R3911BD1 User Manual

UM2042

User manual

Discovery kit for the ST25R3911B

high performance HF reader / NFC initiator

Introduction

The ST25R3911 B-DISCO is a ready-to-use development kit to evaluate the functions of the
high performance HF reader / NFC initiator ST25R3911B in Reader mode for contactless
applications.

The ST25R3911B-DISCO kit supports

• ISO 18092 (NFCIP-1) active P2P

• ISO 14443A and ISO14443B

• ISO 15693

• FeliCa™

• VHBR, with 6.8 Mbit/s PCD to PICC framing and 3.4 Mbit/s PICC to PCD framing

• Up to 1.4 W output power with differential antenna

• Possibility of driving two antennas in single ended mode, with automatic antenna tuning

(AAT) system

• Inductive and capacitive Wake-up

• User selectable and automatic gain control

®

• Transparent and Stream modes to implement MIFARE
custom protocols

The evaluation kit includes

• the STM32L476RET6, a 32-bit microcontroller with 512 KB of Flash memory

• a 105 mm x 52 mm, two turns antenna etched on the PCB, and its VHBR tuning circuit

• a Micro-USB connector for communication with the host PC and board powering

• six LEDs indicating the presence of the RF field and of the protocol used to communicate.

Classic compliant or other

Figure 1. ST25R3911B-DISCO PCB (top view)

July 2017 DocID029132 Rev 2 1/25

www.st.com

1

Contents UM2042

Contents

1 Quick start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

1.1 Getting started . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

1.2 System requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2 Hardware . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2.1 Block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2.2 Schematics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2.2.1 USB connectivity and power supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.2.2 STM32L4 MCU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.2.3 ST25R3911B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.2.4 Antenna and matching network components . . . . . . . . . . . . . . . . . . . . . . 8

2.3 PCB layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

2.3.1 PCB overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

2.3.2 PCB layers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

3 Antenna matching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

4 Federal Communications Commission (FCC)

and Industry Canada (IC) compliance statements . . . . . . . . . . . . . . . . 22

4.1 FCC Compliance Statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

4.1.1 Part 15.19 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

4.1.2 Part 15.21 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

4.1.3 Part 15.105 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

4.1.4 FCC ID . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

4.2 Formal notices required by the Industry Canada (“IC”) . . . . . . . . . . . . . . 22

4.2.1 Compliance Statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

4.2.2 Declaration de Conformité . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

4.2.3 IC ID . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

5 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

2/25 DocID029132 Rev 2

UM2042 List of tables

List of tables

Table 1. NFC Forum matching alternatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Table 2. Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

DocID029132 Rev 2 3/25

3

List of figures UM2042

List of figures

Figure 1. ST25R3911B-DISCO PCB (top view). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Figure 2. Functional block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Figure 3. Schematics overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Figure 4. USB interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Figure 5. STM32L476 schematics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Figure 6. ST25R3911B schematics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Figure 7. Antenna and matching network schematics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Figure 8. PCB overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Figure 9. PCB layout, top layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Figure 10. PCB layout, mid layer 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Figure 11. PCB layout, mid layer 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Figure 12. PCB layout, bottom layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Figure 13. VHBR matching with an AAT setting of 8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Figure 14. NFC Forum matching with an AAT setting of 11 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

4/25 DocID029132 Rev 2

UM2042 Quick start

1 Quick start

The ST25R3911B-DISCO is connected to a PC via USB to show the features of the
ST25R3911B chip. To do so, use the software STSW-ST25R001 to control all the functions
of the discovery kit.

1.1 Getting started

Connect the discovery kit to a PC using a micro USB cable. The USB port of the PC must be
capable of delivering at least 250 mA at 5 Volt supply.

To control the board, download the software STSW-ST25R001 from www.st.com and install
it. Further information on how to operate the software can be found in the user manual
UM2177 “PC software for the ST25R3911B-DISCO kit”, available on www.st.com.

1.2 System requirements

• Windows® PC (Windows 7 recommended)

• USB port, capable of delivering at least 250 mA at 5 V supply (1.25 W)

• Unit must be supplied by a Safety Extra Low Voltage (SELV) limited power source

through the USB port, the source should not exceed 60 Vdc / 8 A / 100 VA

• Micro-USB cable

DocID029132 Rev 2 5/25

24

Hardware UM2042

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2 Hardware

The PCB (Printed Circuit Board) is connected via USB to the PC. The STSW-ST25R001 PC
software controls the STM32 MCU located on the PCB. The STM32 MCU then operates the
ST25R3911B via SPI.

The ST25R3911B is connected directly to the 5 V supply of the USB bus. An LDO converts
this voltage down to 3.3 V, to supply the microcontroller.

A green LED close to the USB plug indicates if the board is powered. Six blue LEDs indicate
the mode of operation (transmit / receive) and which technologies are in use.

The antenna runs along the PCB perimeter.

2.1 Block diagram

Figure 2 shows the functional block diagram of the board.

Figure 2. Functional block diagram

2.2 Schematics

As indicated in Figure 3, the schematics can be split into four main parts

• USB connectivity and power supply (Figure 4)

• STM32 MCU (Figure 5)

• ST25R3911B (Figure 6)

• Antenna and matching network components (Figure 7)

6/25 DocID029132 Rev 2

UM2042 Hardware

2.2.1 USB connectivity and power supply

The ST25R3911B-DISCO board can be connected via USB to a host device.
Right behind the Micro-USB plug, an ECMF02 common mode filter with ESD protection for

USB 2.0 interface is placed. The common mode filter is connected to VBUS and to the
D+/D- data lines of the USB. All the USB terminals are ESD-protected by the built-in ESD
diodes of the ECMF02.

Additionally , the power supply filter for the 5 V supplies the 3.3 V LDO, that, in turn, supplies
the microcontroller.

A green LED is connected to the USB VBUS supply and shows the USB-power status.

2.2.2 STM32L4 MCU

This schematic includes the microcontroller needed to operate the NFC reader IC.
The MCU is clocked by a 32.768 kHz crystal. The MCU uses an internal PLL to generate the

48 MHz USB clock and the 80 MHz core clock from the provided 32.768 kHz.
Connector P201 is a JTAG/SWD interface to assist in software development. It can be

connected to an external ST-LINK/V2 device using a 9-pin Cortex
The six blue LEDs (LED201 to LED206) show the current mode of communication. If

multiple protocols are active at the same time, then all corresponding LEDs are turned on.
The five resistors (R218 to R222) can be used to disconnect the MCU from SPI interface

header P204. This SPI cross-connect mode can be used to operate th e ST25R3911B with a
different MCU PCB by cross connecting the ST25R3911B SPI to the second MCU PCB.

Connectors P202 and P203 can be used to connect an external UART or I2C host device to
the MCU.

®

-M adapter.

2.2.3 ST25R3911B

The ST25R3911B is directly connected to the filtered 5 V USB supply, and there are
additional supply filtering components placed close to it. The jumper JP301 can be used to
measure the supply current of the chip. If this measurement is performed, the ferrite bead
L301 has to be removed.

Capacitors C301 to C304 provide additional filtering. All decoupling capacitors have been
placed as close as possible to the ST25R3911B. Special care has been taken for C310,
C302, C314 and C301, as they are the decoupling capacitors for the high power driver
stage.

In order to demonstrate the capacitive wake-up feature, two capacitive electrodes are
placed on the PCB. Additional electrodes can b e connected using UFL connectors o n P301
and P302.

For SPI cross-connecting to another reader PCB, the resistors R301 to R305 can be
removed. Then the STM32L4 MCU SPI can be connected to the ST25R3911B on any
customer PCB via header P204.

Thanks to J303 it is possible to bypass the internal VSP_RF regulator, this is required in
case output currents higher than 200 mA need to be supplied.

DocID029132 Rev 2 7/25

24

Hardware UM2042

2.2.4 Antenna and matching network components

This schematic contains the matching network and the automatic antenna tunin g capacitors,
as well as the alternative NFC Forum matching components. In the default configuration,
the ST25R3911B-DISCO is populated with a VHBR matching, with communication speeds
up to 3.4 Mbps.

To support VHBR, the antenna is matched to a system Q-Factor of 8. By switching to the
NFC Forum matching components the system Q-Factor is increased to 16. This can
increase the read range up to 20%, depending on the used communication technology, but
limits the maximum supported communication bit rate to 848 kbps. Additional details about
antenna matching can be found on www.st.com/st25r.

8/25 DocID029132 Rev 2

UM2042 Hardware

Figure 3. Schematics overview

4

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A A

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B B

C C

D D

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DocID029132 Rev 2 9/25

Hardware UM2042

ST25

G103

Logo_ST25

ST Microelectronics

G104

GND

Logo_STM

PM/USB_con

V_RF

3V3

PM/USB_con

V_RF

3_3V

USBD_N

USBD_N

USBD_P

USBD_P

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ESD

G101

Logo_ESD

RoHS

G102

Logo_RoHS

4

LED101

3

V_RF

R101

C103

C102

C_1μ_0603_X5R

Figure 4. USB interface

2

1

L101

FB_0603

USBD_N

5

6

D-

GND

D-2D+3ID

VBUS

U101

1

2

1

D-

PWR

P101

USB Interface

C101

C_10μ_0603_X5R

USBD_P

7

D+

3

D+

C_10μ_0603_X5R

8

GND

ECMF02-4CMX8

4

4

5

ID

GND

Shield

J101

6

μUSB

closed 0R

L103

FB_0603_0R

L102

FB_0603_0R

GNDGND

3V3

3

U102 LD39050PU33R

6

V_RF

3V3 LDO

PG

VI

C106

C105

4

VO

EN

1

C104

C_2μ2_0402_X5R

C_10n_0402_X7R

5

NC

GND

0

GND

2

C_1μ_0603_X5R

2

GND

GND

1

A A

B B

10/25 DocID029132 Rev 2

C C

D D

UM2042 Hardware

6

V

5

4

3

Figure 5. STM32L476 schematics

2

1

LED6

LED5

LED4

LED3

R206

LED2

R205

LED1

R203

R202

LED201

Interface

T_JTMS

T_JTCK

R207

R201

R204

3V3

123456789

P201

SWD

T_SWO

AVDD

LED3

LED4

26

28

27

PB0

PB2

PB355PB456PB557PB658PB759PB861PB9

PB1/VREF+

PA014PA115PA216PA3/SAR_VREF+

PA420PA521PA622PA7

U201A

17

497-15872-ND

Microcontroller

IRQ_MCU

LED1

LED2

R209

R208

LED205

LED204

LED203

LED202

T_JTDI

T_SWO

R210

R211

SDA

SCL

/SS_MCU

LED5

62

PA841PA942PA1043PA1144PA1245PA1346PA1449PA15

23

SCLK_MCU

MISO_MCU

MOSI_MCU

UART_TX

LED6

LED206

T_NRST

10

30

29

PB10/PE8

MCU_D_N

UART_RX

PM/USB_con

V_RF

Header 10

AVDD

33

35

36

PB13/PB1434PB14/PB15

PB11/VCAP1

PB12/SD_VREF+

50

T_JTMS

T_JTCK

T_JTDI

MCU_D_P

V_RF

3_3V

3V3

MCU_D_P

R212

USBD_P

USBD_N MCU_D_N

40

PC839PC9

PB15/PD8

PC08PC19PC210PC3

LP_UART_RX

LP_UART_TX

PM/USB_con

USBD_N

USBD_P

USBD_N

USBD_P

R213

C202

C201

PC1051PC1152PC12

11

P202

C_56p_0402

C_56p_0402

C203

2

53

3

PC13

PC14 - OSC32_IN

PC424PC5

PC637PC7

25

V_RF

3_3V

SPI/Power_Con

V_RF

3V3

3V3

LP_UART_RX

LP_UART_TX

R214

R215

123

4

d.n.p.

C204

C_4p3_0402

X201

32.768 kHz

4

PC15 - OSC32_OUT

STM32L476RE

38

SPI/Power_Con

SEN

INTR

MISO

MOSI

SCLK

INTR

MISO

MOSI

SCLK

SEN

3V3

SDA

SCL

R216

123

P203

C_4p3_0402

C205

MCU_CLK

R217

4

d.n.p.

d.n.p.

Y201

SCLKSCLK_MCU

R218

R219

S201

T_NRST

7

NRST

PF0/PD0/PH0 - OSC_IN

U201B

5

d.n.p.

C206

LP_UART_RX

LP_UART_TXUART_TX

J201

open

J202

open

UART_RX

MOSI

MOSI_MCU

Case

60

BOOT0

PF1/PD1/PH1 - OSC_OUT

6

d.n.p.

3V3

INTR

R220

R221

IRQ_MCU

C207

12

VSSA

VBAT/VLCD

1

L201

GND

SEN

MISO

R222

MISO_MCU

/SS_MCU

C_100n_0402_X7R

63

31

54

PD2

VSS/VCAP1

VDDA/VREF+

VDD

13

32

64

AVDD

FB_0603

8
7

V_RF

6
5

3V3

4
3
2
1

3V3

Case

S202

C208

18

47

VSS

VSS/PF4/PA3

VSS/VCAP2/PF6

VDD/PF5

VDD/VUSB/VSA/PF7

VDD

STM32L476RE

19

48

P204 d.n.p.

C_100n_0402_X7R

R223

DD

C216

C21

in 12+

A

AVDD

C215

Pin 1

C214

4 Pin 31+

C213

in 63+

C212

C211

Pin 47+

C210

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5R

C_100n_0402_X7R

C_1μ_0402_X5R

C_100n_0402_X7R

C_100n_0402_X7R

C_100n_0402_X7R

1

C_4μ7_0402_X5R

3V3

A A

B B

C C

C_4μ7_0402_X5R

D D

C_100n_0402_X7R

C209

Pin 18+19 Pin 47+48 Pin 63+64 Pin 12+13Pin 31+32 Pin 1

Pin 18+

DocID029132 Rev 2 11/25

Hardware UM2042

SPI/Power_Con

4

Controller Interface

V_RF

SPI/Power_Con

V_RF

3V3

3_3V

INTR

R301

INTR_11

MISO

MOSI

R303

R302

MISO_11

MOSI_11

SEN

SCLK

R305

R304

SCLK_11

SEN_11

MCU_CLK

Antenna_Con

RFI1

RFI2

RFO1

RFO2

TRIM1_0

RFO1

RFO2

TRIM1_1

TRIM1_0

TRIM1_1

TRIM1_2

Antenna_Con

RFI2

RFI1

Antenna Connection

TRIM1_2

TRIM1_3

TRIM2_0

TRIM2_0

TRIM1_3

TRIM2_1

TRIM2_2

TRIM2_1

TRIM2_2

TRIM2_3

TRIM2_3

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Figure 6. ST25R391 1B schematics

3

TRIM1_0

TRIM1_1

TRIM1_2

U301

ST25R3911B

V_RF

d.n.p.

GND

C301

V_RF_3911

L301

C_1μ_0402_X5R

3V3

FB_0603

JP301

GND

C_100n_0402_X7R

C302

C304

C_100n_0402_X7R

C303

d.n.p.

d.n.p.

TRIM1_019TRIM2_0

TRIM1_117TRIM2_1

VDD

8

1

MISO29MOSI30SCLK

/SS

GND

32

SEN_11

MISO_11

MOSI_11

J302

J301

2

1

ST25R3911 NFC Initiator / HF Reader

TRIM1_3

TRIM2_0

TRIM2_1

TRIM2_2

TRIM2_3

14

20

16

18

TRIM1_313TRIM2_3

TRIM1_215TRIM2_2

VDD_IO

ST25R3911

NFC Initiator / HF Reader IC

CSO

IRQ27MCU_CLK

CSI

2

28

31

SCLK_11

INTR_11

P301

R306

CSO_out

2

CSO

25

CSI

R307

RFO1

RFO2

11

RFO110RFO2

5

CSI_out

GND

GND

GND

1

3

XTO4XTI

RFI1

RFI122RFI2

C306

C305

RFI2

23

EP VSUB
VSS
AGD

VSN_D
VSP_D

VSN_RF
VSP_RF

VSN_A
VSP_A

C307

C_8p2_0402

Y301

C_12p_0402

GND GND

d.n.p.

33
21
24

6
3

12

9

26

7

GND

C308

GND

C_12p_0402

P302

VSP_RF

J303

V_RF_3911

C_8p2_0402

2

open

GND

GND

AGD

VSP_D

VSP_RF

VSP_A

1

3

C312

C311

C310

C309

d.n.p.

C_1μ_0402_X5R

C_10n_0402_X7R

C316

C315

C_2μ2_0402_X5R

C_10n_0402_X7R

C314

C_10n_0402_X7R

C313

C_10n_0402_X7R

C_2μ2_0402_X5R

GNDGND

GND

GNDGND

C_2μ2_0402_X5R

GND

3

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D D

UM2042 Hardware

Figure 7. Antenna and matching network schematics

4

4

MDG NFC & Reader Competence Center

Antenna Loop

J404

closed 0R

J401

closed 0R

123

J405

GND

C408

C_120p_0603

d.n.p.

C407

C409

closed 0R

R402

C410

C_180p_0603

C_680p_0603

L402

270n

C411

C_10p_0603

C412

C_82p_0603

GND

J402

3

C401

C_82p_0603

GND

2

C402

C_10p_0603

C403

R401

L401

C406

C404

C_180p_0603

C405

C_680p_0603

270n

C_120p_0603

d.n.p.

GND

R401_NFCF

R402_NFCF

C410_NFCF

C_120p_0603

C_120p_0603

GND GND

C403_NFCF

NFC Forum matching

TRIM1TRIM2

closed 0R

J407

C_5p6_0402

C_12p_0402

C_27p_0402

C416

TRIM1_0

C_5p6_0402

C415

C418

C_12p_0402

C417

C420

TRIM1_1

J406

C419

C_56p_0402

C422

TRIM1_2

closed 0R

C_56p_0402

C_27p_0402

C421

TRIM1_3

77

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J403

RFI1

TRIM1

Antenna Circuit incl. EMI Filter and Matching

1

A A

RFO1

RFO2

B B

DocID029132 Rev 2 13/25

TRIM2

RFI2

TRIM2_0

TRIM2_1

TRIM2_2

RFO1

RFO1

RFO2

RFO2

TRIM2_3

TRIM1_0

TRIM1_1

TRIM1_2

TRIM1_0

TRIM1_1

TRIM1_2

Antenna_Con

TRIM1_3

TRIM1_3

Trim Capacitor Banks

RFI2

RFI1

RFI1

RFI2

Antenna_Con

Antenna Connection

C C

TRIM2_1

TRIM2_0

TRIM2_0

TRIM2_1

TRIM2_3

TRIM2_2

TRIM2_2

TRIM2_3

D D

1

Hardware UM2042

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2.3 PCB layout

2.3.1 PCB overview

The PCB (see Figure 8) is organized in two halves

• Left side: the SPI header P204 and the digital / MCU sections

• Right side: the analog parts and the ST25R3911B.

The whole PCB is surrounded by a two turns NFC antenna.

Figure 8. PCB overview

The boot button can be found right above the I2C header. If this button is pressed during the
powering or the resetting of the board, the STM32L4 will enter the boot loader mode. The
reset button is positioned between the JTAG/SWD header and the I2C header.

2.3.2 PCB layers

The PCB layout is designed considering that the ST25R3911B is a high power RF
transmitter, hence the decoupling cap acitors are located as close as possible to the positive
and negative power supply pins, for example VSP_RF and VSN_RF.

Since the chip is using a differential output driver stage, the antenna matching network is
treated as a differential network. The space between the components is kept as small as
possible and the whole network is routed in a completely symmetrical way.

Via stitching and via shielding is used to maintain a low impedance and prevent short return
current loops. The RF traces are protected by via stitching in combination with guard rings
to create a via wall. This keeps the PCB electromagnetically “quiet”.

A via shield is used to create a vertical copper barrier th rough the PCB. This help s to reduce
crosstalk and electromagnetic interference in any route carrying an RF signal. The RFI
traces and AAT lanes are routed as close as possible to each other.

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UM2042 Hardware

Top layer

The top layer (Figure 9) contains most of the components and PCB traces. The unused
areas around the ICs are filled with GND planes, guarded using via stitching. Furthermore,
important analog traces are surrounded by GND vias.

Mid layer 1

This layer (Figure 10) is a pure GND plane, providing a low ohmic DC path for the GND
connection.

Mid layer 2

Mid layer 2 (Figure 11) is used for the power distribution. It contains the power planes for the
5 V supply of the ST25R3911B and the 3.3 V supply of the microcontroller.

Bottom layer

The bottom layer (Figure 12) is mainly a GND plane, but some traces are routed through it.

DocID029132 Rev 2 15/25

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Hardware UM2042

Figure 9. PCB layout, top layer

16/25 DocID029132 Rev 2

UM2042 Hardware

Figure 10. PCB layout, mid layer 1

DocID029132 Rev 2 17/25

Hardware UM2042

Figure 11. PCB layout, mid layer 2

18/25 DocID029132 Rev 2

UM2042 Hardware

Figure 12. PCB layout, bottom layer

DocID029132 Rev 2 19/25

Antenna matching UM2042

3 Antenna matching

The default matching network assembled enables VHBR operation up to 3.4 Mbps.
Components for an optional NFC Forum matching are placed on the board. Exchan ging the

components as indicated in Table 1 will increase the Q factor of the antenna system. VHBR
communication at 3.4 Mbps and 1.7 Mbps bit rate will not be supported anymore, but the
read range for lower data rate applications will increase, up to 20%.

The matching impedance will remain the same when switching between the two matchings.

VHBR matching

The VHBR matching is designed with a target Q-Factor of 8. The matching impedance is
around 12.8 + j5 . The HW based AAT algorithm will typically adjust to an AAT value of 8
(see Figure 13).

Figure 13. VHBR matching with an AAT setting of 8

NFC Forum matching

The NFC Forum matching is designed with a target Q-Factor of 16.
To switch to the NFC Forum matching the user needs to change the components listed in

Table 1.

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UM2042 Antenna matching

Table 1. NFC Forum matching alternatives

Default assembly Value NFC Forum replacement Value

C403 80 pF C403_NFCF 120 pF
C410 180 pF C410_NFCF 120 pF
R401 3R9 R401_NFCF 1R96
R402 3R9 R402_NFCF 1R96

With the new assembled values, the matching impedance looks as in Figure 14, with a
value close to 11 + j6 .

Figure 14. NFC Forum matching with an AAT setting of 11

The HW based AAT algorithm will typically adjust to an AAT value of 11. Due to the higher
Q-Factor the voltage on the antenna is also increasing. To have the receiver in an optimum
signal level range, the capacitors C401 and C412 can be increased to 100 pF.

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Federal Communications Commission (FCC) and Industry Canada (IC) compliance statements

4 Federal Communications Commission (FCC)

and Industry Canada (IC) compliance statements

4.1 FCC Compliance Statement

4.1.1 Part 15.19

This device complies with Part 15 of the FCC Rules. Operation is subject to the following
two conditions: (1) this device may not cause harmful interference, and (2) this device must
accept any interference received, including interference that may cause undesired
operation.

4.1.2 Part 15.21

Any changes or modifications to this equipment not expressly approved by
STMicroelectronics may cause harmful interference and void the user’s authority to operate
this equipment.

4.1.3 Part 15.105

This equipment has been tested and found to comply with the limits for a Class B digital
device, pursuant to part 15 of the FCC Rules. These limits are designed to provide
reasonable protection against harmful interference in a residential installation. This
equipment generates, uses and can radiate radio frequency energy and, if not installed an d
used in accordance with the instructions, may cause harmful interference to radio
communications. However, there is no guarantee that interference will not occur in a
particular installation. If this equipment does cause harmful interference to radio or
television reception, which can be determined by turning the equipment off and on, the user
is encouraged to try to correct the interference by one or more of the following measures:

• Reorient or relocate the receiving antenna.

• Increase the separation between the equipment and receiver.

• Connect the equipment into an outlet on a circuit different from that to which the

receiver is connected.

• Consult the dealer or an experienced radio/ TV technician for help.

4.1.4 FCC ID

FCC ID: YCPR3911BD1

4.2 Formal notices required by the Industry Canada (“IC”)

4.2.1 Compliance Statement

This device complies with Industry Canada license-exempt RSS standard(s). Operation is
subject to the following two conditions: (1) this device may not cause interference, and (2)
this device must accept any interference, including interference that may cause undesired
operation.

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UM2042Federal Communications Commission (FCC) and Industry Canada (IC) compliance state-

4.2.2 Declaration de Conformité

Le présent appareil est conforme aux CNR d’Industrie Canada applicables aux appareils
radio exempts de licence. L’exploitation est autorisée aux deux conditions suivantes: (1)
l’appareil ne doit pas produire de brouillage, et (2) l’utilisateur de l’appareil doit accepter tout
brouillage radioélectrique subi, même si le brouillage est susceptible d’en compromettre le
fonctionnement.

4.2.3 IC ID

IC ID: 8976B-R3911BD1

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Revision history UM2042

5 Revision history

Table 2. Document revision history

Date Revision Changes

23-Jun-2017 1 Initial release.

Added Section 4.1.3: Part 15.105.

25-Jul-2017 2

Updated Section 4.1.4: FCC ID and Section 4.2.3: IC ID.
Updated Figure 8: PCB overview, Figure 9: PCB layout, top layer and

Figure 12: PCB layout, bottom layer.

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UM2042

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