Silicon Laboratories BRD4257A Manuale utente

EFR32FG14 2400/915 MHz Dual Band

19 dBm Radio Board

BRD4257A Reference Manual

The BRD4257A Flex Gecko Radio Board enables developers to develop proprietary

wireless applications. The board contains a dual-band Flex Gecko Wireless System-on-

Chip and it is optimized for operating at 19 dBm output power. For the 2.4 GHz band

with the on-board printed antenna and UFL connector, radiated and conducted testing is

supported. For the 915 MHz band, the on-board SMA connector enables conducted

testing and attachment of external whip antenna for radiated tests.

The BRD4257A Flex Gecko Radio Board plugs into the Wireless Starter Kit Mainboard,

which is included with the Flex Gecko Starter Kit and gives access to display, buttons

and additional features from Expansion Boards. With the supporting Simplicity Studio

suite of tools, developers can take advantage of graphical wireless application develop-

ment and visual energy profiling and optimization. The board also serves as an RF ref-

erence design for applications targeting 2.4 GHz and 915 MHz dual band wireless oper-

ation with 19 dBm output power.

RADIO BOARD FEATURES

• Wireless SoC:

EFR32FG14P233F256GM48

•CPU core: ARM Cortex®-M4 with FPU

• Flash memory: 256 kB

• RAM: 32 kB

• Operation frequency: 2.4 GHz + 915 MHz

• Transmit power: 19 dBm

• 2.4 GHz: Integrated PCB antenna, UFL

connector (optional)

• 915 MHz: Single SMA connector both for

transmit and receive

• Crystals for LFXO and HFXO: 32.768 kHz

and 38.4 MHz

• 8 Mbit low-power serial flash for over-the-

air updates

This document contains a brief introduction and description of the BRD4257A Radio

Board features, focusing on the RF sections and performance.

silabs.com | Building a more connected world. Rev. 1.00

Table of Contents

1. Introduction ................................

2. Radio Board Connector ...........................5

2.1 Introduction...............................5

2.2 Radio Board Connector Pin Associations.....................5

3. Radio Board Block Summary .........................6

3.1 Introduction...............................6

3.2 Radio Board Block Diagram .........................6

3.3 Radio Board Block Description ........................6

3.3.1 Wireless MCU............................6

3.3.2 LF Crystal Oscillator (LFXO) .......................6

3.3.3 HF Crystal Oscillator (HFXO).......................6

3.3.4 Matching Network for Sub-GHz ......................6

3.3.5 Matching Network for 2.4 GHz ......................7

3.3.6 SMA Connector ...........................7

3.3.7 UFL Connector ...........................7

3.3.8 Radio Board Connectors ........................7

3.3.9 Inverted-F Antenna ..........................7

3.3.10 Serial Flash ............................7

3.3.11 Serial EEPROM...........................7

4. RF Section ................................8

4.1 Introduction...............................8

4.2 Schematic of the RF Matching Network .....................8

4.2.1 Description of the Sub-GHz RF Matching ..................8

4.2.2 Description of the 2.4 GHz RF Matching ...................8

4.3 RF Section Power Supply ..........................8

4.4 Bill of Materials for the sub-GHz Matching ....................8

4.5 Bill of Materials for the 2.4 GHz Matching ....................9

4.6 Inverted-F Antenna ............................9

5. Mechanical Details .............................11

6. EMC Compliance ............................. 12

6.1 Introduction...............................12

6.2 EMC Regulations for 915 MHz ........................12

6.2.1 FCC15.247 Emission Limits for the 902-928 MHz Band ..............12

6.3 ETSI EN 300-328 Emission Limits for the 2400-2483.5 MHz Band ............12

6.4 FCC15.247 Emission Limits for the 2400-2483.5 MHz Band ..............12

6.5 Applied Emission Limits for the 2.4 GHz Band ...................12

7. RF Performance ............................. 13

7.1 Conducted Power Measurements .......................13

silabs.com | Building a more connected world. Rev. 1.00 | 2

7.1.1 Conducted Measurements in the 915 MHz Band ................13

7.1.2 Conducted Measurements in the 2.4 GHz Band ................14

7.2 Radiated Power Measurements ........................15

7.2.1 Radiated Measurements in the 915 MHz Band .................16

7.2.2 Radiated Measurements in the 2.4 GHz Band .................16

8. EMC Compliance Recommendations ..................... 17

8.1 Recommendations for 915 MHz FCC 15.247 Compliance ...............17

8.2 Recommendations for 2.4 GHz ETSI EN 300-328 Compliance .............17

8.3 Recommendations for 2.4 GHz FCC 15.247 Compliance ...............17

9. Board Revision History .......................... 18

10. Errata................................. 19

11. Document Revision History ........................ 20

silabs.com | Building a more connected world. Rev. 1.00 | 3

1. Introduction

The EFR32 Flex Gecko Radio Boards provide a development platform (together with the Wireless Starter Kit Mainboard) for the Silicon

Labs EFR32 Flex Gecko Wireless System-on-Chips and serve as reference designs for the matching networks of the RF interfaces.

The BRD4257A Radio Board supports dual-band operation with its integrated sub-GHz ISM band and 2.4 GHz band transceivers. The

sub-GHz section is designed to operate in the US FCC 902-928 MHz band with an external whip antenna, the 2.4 GHz section is de-

signed to operate at the 2400-2483.5 MHz band with the on-board printed antenna. The matching networks are optimized for operating

at 19 dBm output power.

To develop and/or evaluate the EFR32 Flex Gecko, the BRD4257A Radio Board can be connected to the Wireless Starter Kit Main-

board to get access to display, buttons and additional features from Expansion Boards and also to evaluate the performance of the RF

interfaces.

BRD4257A Reference Manual

Introduction

silabs.com | Building a more connected world. Rev. 1.00 | 4

2. Radio Board Connector

2.1 Introduction

The board-to-board connector scheme allows access to all EFR32FG14 GPIO pins as well as the RESETn signal. For more information

on the functions of the available pins, see the EFR32FG14 data sheet.

2.2 Radio Board Connector Pin Associations

The figure below shows the mapping between the connector and the EFR32FG14 pins and their function on the Wireless Starter Kit

Mainboard.

GND

F9 / PA3 / VCOM.#RTS_#CS

3v3

NC / P36

P200

Upper Row

NC / P38

NC / P40

NC / P42

NC / P44

DEBUG.TMS_SWDIO / PF1 / F0

DISP_ENABLE / SENSOR_ENABLE / PD15 / F14

UIF_BUTTON0 / PF6 / F12

UIF_LED0 / PF4 / F10

VCOM.#CTS_SCLK / PA2 / F8

UIF_BUTTON0 / PF6 / P4

DEBUG.TDO_SWO / PF2 / F2

DISP_SI / PC6 / F16

VCOM.TX_MOSI / PA0 / F6

PTI.DATA / PB12 / F20

DISP_EXTCOMIN / PD13 / F18

USB_VBUS

Board ID SCL

GND

Board ID SDA

USB_VREG

F7 / PA1 / VCOM.RX_MISO

F5 / PA5 / VCOM_ENABLE

F3 / PF3 / DEBUG.TDI

F1 / PF0 / DEBUG.TCK_SWCLK

P45 / NC

P43 / NC

P41 / NC

P39 / NC

P37 / PD15 / DISP_ENABLE / SENSOR_ENABLE

F11 / PF5 / UIF_LED1

F13 / PF7 / UIF_BUTTON1

F15 / PC8 / DISP_SCLK

F17 / PD14 / DISP_SCS

F19 / PB13 / PTI.SYNC

F21 / PB11 / PTI.CLK

GND VMCU_IN

VCOM.#CTS_SCLK / PA2 / P0

P201

Lower Row

VCOM.#RTS_#CS / PA3 / P2

UIF_BUTTON0 / PF6 / P4

UIF_BUTTON1 / PF7 / P6

GND VRF_IN

P35 / PD15 / DISP_ENABLE / SENSOR_ENABLE

P7 / PC9

P5 / PC8 / DISP_SCLK

P3 / PC7

P1 / PC6 / DISP_SI

P33 / PD14 / DISP_SCS

P31 / PD13 / DISP_EXTCOMIN

P29 / NC

P27 / NC

P25 / NC

P23 / NC

P21 / NC

P19 / NC

P17 / NC

P15 / NC

P13 / PC11

P11 / PA1 / VCOM.RX_MISO

P9 / PA0 / VCOM.TX_MOSI

NC / P34

UIF_LED1 / PF5 / P32

NC / P30

DEBUG.TDO_SWO / PF2 / P28

DEBUG.TMS_SWDIO / PF1 / P26

DEBUG.TCK_SWCLK / PF0 / P24

PTI.SYNC / PB13 / P22

PTI.DATA / PB12 / P20

PTI.CLK / PB11 / P18

VCOM_ENABLE / PA5 / P16

PA4 / P14

PC10 / P12

DEBUG.TDI / PF3 / P10

UIF_LED0 / PF4 / P8

Figure 2.1. BRD4257A Radio Board Connector Pin Mapping

BRD4257A Reference Manual

Radio Board Connector

silabs.com | Building a more connected world. Rev. 1.00 | 5

3. Radio Board Block Summary

3.1 Introduction

This section gives a short introduction to the blocks of the BRD4257A Radio Board.

3.2 Radio Board Block Diagram

The block diagram of the BRD4257A Radio Board is shown in the figure below.

EFR32

Inverted-F

PCB

Antenna

2.4 GHz RF

UFL

Connector

Crystal

32.768k

Crystal

38.4M

Radio

Board

Connectors

8 Mbit

MX25R

Serial Flash

I2C

24AA024

Serial EEPROM

Matching

Network &

Output

Selection

GPIO

UART

Debug

Packet Trace

AEM

I2C

SPI

2.4 GHz RF

SubGHz RF

Matching

Network &

DC Bias

SubGHz RF SMA

Connector

EFR32

Wireless SoC

Figure 3.1. BRD4257A Block Diagram

3.3 Radio Board Block Description

3.3.1 Wireless MCU

The BRD4257A Flex Gecko Radio Board incorporates an EFR32FG14P233F256GM48 Wireless System-on-Chip featuring 32-bit Cor-

tex®-M4 with FPU core, 256 kB of flash memory, 32 kB of RAM, an integrated 2.4 GHz band and an integrated sub-GHz ISM band

transceiver with output power up to 19 dBm. For additional information on the EFR32FG14P233F256GM48, refer to the EFR32FG14

Data Sheet.

3.3.2 LF Crystal Oscillator (LFXO)

The BRD4257A Radio Board has a 32.768 kHz crystal mounted. For details regarding the crystal configuration, refer to Application

Note "AN0016: Oscillator Design Considerations".

3.3.3 HF Crystal Oscillator (HFXO)

The BRD4257A Radio Board has a 38.4 MHz crystal mounted. For details regarding the crystal configuration, refer to Application Note

"AN0016: Oscillator Design Considerations".

3.3.4 Matching Network for Sub-GHz

The BRD4257A Radio Board incorporates a sub-GHz matching network which connects both the sub-GHz TX and RX pins of the

EFR32FG14 to the SMA connector to be able to transmit and receive with one antenna. The component values have been optimized

for the 915 MHz band RF performance and current consumption with 19 dBm output power.

For a detailed description of the matching network see Chapter 4.2.1 Description of the Sub-GHz RF Matching.

BRD4257A Reference Manual

Radio Board Block Summary

silabs.com | Building a more connected world. Rev. 1.00 | 6

3.3.5 Matching Network for 2.4 GHz

The BRD4257A Radio Board incorporates a 2.4 GHz matching network which connects the 2.4 GHz TRX pin of the EFR32FG14 to the

one on-board printed inverted-F antenna. The component values have been optimized for the 2.4 GHz band RF performance and cur-

rent consumption with 19 dBm output power.

For a detailed description of the matching network, see Chapter 4.2.2 Description of the 2.4 GHz RF Matching.

3.3.6 SMA Connector

To be able to perform conducted measurements or mount external antenna for radiated measurements, range tests etc., Silicon Labs

added an SMA connector to the Radio Board. The connector allows an external 50 Ohm cable or antenna to be connected during de-

sign verification or testing.

3.3.7 UFL Connector

To be able to perform conducted measurements, Silicon Labs added a UFL connector to the Radio Board. The connector allows an

external 50 Ohm cable or antenna to be connected during design verification or testing.

Note: By default, the output of the matching network is connected to the printed inverted-F antenna by a series component. It can be

connected to the UFL connector as well through a series 0 Ohm resistor, which is not mounted by default. For conducted measure-

ments through the UFL connector, the series component to the antenna should be removed and the 0 Ohm resistor should be mounted

(see Chapter 4.2.2 Description of the 2.4 GHz RF Matching for further details).

3.3.8 Radio Board Connectors

Two dual-row, 0.05” pitch polarized connectors make up the BRD4257A Radio Board interface to the Wireless Starter Kit Mainboard.

For more information on the pin mapping between the EFR32FG14P233F256GM48 and the Radio Board Connector, refer to Chapter

2.2 Radio Board Connector Pin Associations.

3.3.9 Inverted-F Antenna

The BRD4257A Radio Board includes a printed inverted-F antenna (IFA) tuned to have close to 50 Ohm impedance at the 2.4 GHz

band.

For detailed description of the antenna, see Chapter 4.6 Inverted-F Antenna.

3.3.10 Serial Flash

The BRD4257A Radio Board is equipped with an 8 Mbit Macronix MX25R SPI flash that is connected directly to the EFR32FG14 to

support over-the-air (OTA) updates. For additional information on the pin mapping see the schematic of the BRD4257A.

3.3.11 Serial EEPROM

The BRD4257A Radio Board is equipped with a serial I2C EEPROM for board identification and to store additional board related infor-

mation.

BRD4257A Reference Manual

Radio Board Block Summary

silabs.com | Building a more connected world. Rev. 1.00 | 7

4. RF Section

4.1 Introduction

This section gives a short introduction to the RF section of the BRD4257A Radio Board.

4.2 Schematic of the RF Matching Network

The schematic of the RF section of the BRD4257A Radio Board is shown in the following figure.

GND

VBIAS

GND

C10

U.FL

Ground

RF I/ORF Crystal

RF Analog Power

PA Power

U1B

EFR32

2G4RF_IOP 20

2G4RF_ION 19

RFVDD

HFXI

HFXO

PAVDD

RFVSS

PAVSS

SUBGRF_OP 13

SUBGRF_ON 14

SUBGRF_IP 15

SUBGRF_IN 16

TP1

BAL1

0900BL15C050

SE 1

BAL2

BAL1

BIAS 2

GND 5

N/C

AT1

INVERTED_F

SMA

L5 C5

Sub-GHz Matching Network

TRX Matching &

Filter

Inverted-F

Antenna

UFL

Connector

TRX Matching

Discrete Balun

GND

VDCDC

PAVDD

GND

VBIAS

38.400 MHz

C107

10P

L102

BLM18AG601SN1

1 2

L103

BLM18AG601SN1

1 2

C102

100P

C103

10P

C106

220N

Supply Filtering

High Frequency

Crystal

2.4 GHz Matching

Network

2.4 GHz Path

Selection

SMA

Connector

Sub-GHz PA

Power Supply

Figure 4.1. Schematic of the RF Section of the BRD4257A

4.2.1 Description of the Sub-GHz RF Matching

The sub-GHz matching network connects the differential TX outputs and RX inputs of the sub-GHz RF port to the SMA connector while

transforming the impedances to 50 Ohm. Careful design procedure was followed to ensure that the RX input circuitry does not load

down the TX output path while in TX mode and that the TX output circuitry does not degrade receive performance while in RX mode.

The matching includes a differential impedance matching circuitry, a discrete balanced-unbalanced transformer and a filter section. The

targeted output power is 19 dBm at 915 MHz.

4.2.2 Description of the 2.4 GHz RF Matching

The 2.4 GHz matching connects the 2G4RF_IOP pin to the on-board printed Inverted-F Antenna. The 2G4RF_ION pin is connected to

ground. For higher output powers (13 dBm and above) beside the impedance matching circuitry it is recommended to use additional

harmonic filtering as well at the RF output. The targeted output power of the BRD4257A board is 19 dBm. Therefore, the RF output of

the IC is connected to the antenna through a four-element impedance matching and harmonic filter circuitry.

For conducted measurements, the output of the matching network can also be connected to the UFL connector by relocating the series

R1 resistor to the R2 resistor position between the output of the matching and the UFL connector.

4.3 RF Section Power Supply

On the BRD4257A Radio Board the supply pin of the radio (RFVDD) is connected directly of the output of the on-chip DC-DC converter

while the supply for the sub-GHz and 2.4 GHz power amplifiers (SUBGRF_ON, SUBGRF_OP and PAVDD pins) is provided directly by

the Motherboard. This way, by default, the DC-DC converter provides 1.8 V for the RF analog section, the Motherboard provides 3.3 V

for the PAs (for details, see the schematic of the BRD4257A).

4.4 Bill of Materials for the sub-GHz Matching

The Bill of Materials of the sub-GHz matching network of the BRD4257A Radio Board is shown in the following table.

BRD4257A Reference Manual

RF Section

silabs.com | Building a more connected world. Rev. 1.00 | 8

Table 4.1. Bill of Materials for the BRD4257A Sub-GHz RF Matching Network

Component Name Value Manufacturer Part Number

L3 3.3 nH Murata LQW15AN3N3B80D

L4 3.3 nH Murata LQW15AN3N3B80D

L5 18 nH Murata LQW15AN18NG00D

L6 10 nH Murata LQW15AN10NJ00D

L7 10 nH Murata LQW15AN10NJ00D

C3 1.8 pF Murata GRM1555C1H1R8WA01D

C4 1.8 pF Murata GRM1555C1H1R8WA01D

C5 3.9 pF Murata GRM1555C1H3R9WA01D

C6 3.3 pF Murata GRM1555C1H3R3BA01D

C7 5.6 pF Murata GRM1555C1H5R6BA01D

C8 3.3 pF Murata GRM1555C1H3R3BA01D

C10 56 pF Murata GRM1555C1H560GA01D

4.5 Bill of Materials for the 2.4 GHz Matching

The Bill of Materials of the 2.4 GHz matching network of the BRD4257A Radio Board is shown in the following table.

Table 4.2. Bill of Materials for the BRD4257A 2.4GHz RF Matching Network

Component Name Value Manufacturer Part Number

L1 1.8 nH Murata LQP15MN1N8W02D

L2 3.0 nH Murata LQP15MN3N0W02D

C1 2.0 pF Murata GRM1555C1H2R0WA01D

C2 1.0 pF Murata GRM1555C1H1R0WA01D

4.6 Inverted-F Antenna

The BRD4257A Radio Board includes an on-board printed inverted-F antenna tuned for the 2.4 GHz band. Due to the design restric-

tions of the Radio Board, the input of the antenna and the output of the matching network can't be placed directly next to each other.

Therefore, a 50 Ohm transmission line was necessary to connect them. The resulting impedance and reflection measured at the output

of the matcing network are shown in the following figure. As it can be observed, the impedance is close to 50 Ohm (the reflection is

around or better than -10 dB) for the entire 2.4 GHz band.

BRD4257A Reference Manual

RF Section

silabs.com | Building a more connected world. Rev. 1.00 | 9

Figure 4.2. Impedance and Reflection of the Inverted-F Antenna of the BRD4257A Board Measured from the Matching Output

BRD4257A Reference Manual

RF Section

silabs.com | Building a more connected world. Rev. 1.00 | 10

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