SILICON LABS BRD4188B 2.4 GHz 20 dBm Antenna Diversity Radio Board Instruction Manual

SILICON LABS BRD4188B 2.4 GHz 20 dBm Antenna Diversity Radio Board

Product Information

The BRD4188B Radio Board is a development platform designed for developers to create smart homes, lighting, building automation, andAI/ML applications. The board contains a 2.4 GHz Wireless Gecko Wireless System-on-Chip that operates in the 2400-2483.5 MHz band. The RF matching network is optimized for operating at 20 dBm output power. Radiated and conducted testing is supported with the onboard printed antenna and UFL connector.

Product Usage Instructions

To develop and evaluate the EFR32 Wireless Gecko, connect the BRD4188B Radio Board to the Wireless Starter Kit Mainboard. This provides access to the debug interface, Virtual COM port, packet trace, display, buttons, LEDs, and additional features from expansion boards. It also allows for the evaluation of the performance of the RF interface. The Radio Board Connector Pin Associations are described in section 2.2 of the manual. The Mechanical Details of the board are described in section 5. The RF Performance of the board is described in section 7. Conducted Power Measurements with Unmodulated Carrier and Conducted Power Measurements with Modulated Carrier are described in section 7.1.1 and section 7.1.2 respectively. Maximum Radiated Power Measurements are described in section 7.2. For EMC Compliance Recommendations, refer to section 8.1 for 2.4 GHz ETSI EN 300-328 Compliance and section 8.2 for 2.4 GHz FCC 15.247 Compliance. Refer to section 10 for Errata and section 11 for Document Revision History.

The BRD4188B Radio Board enables developers to develop smart homes, lighting, building automation, and AI/ML applications. The board contains a 2.4 GHz Wireless Gecko Wireless System-on-Chip and is optimized for operating at 20 dBm output power. Radiated and conducted testing is supported with the onboard printed antenna and UFL connector. The BRD4188B Radio Board plugs into the Wireless Starter Kit Mainboard, which is included with the Wireless Gecko Starter Kit and gives access to the debug interface, Virtual COM port, packet trace, display, buttons, LEDs, and additional features from expansion boards. With the supporting Simplicity Studio suite of tools, developers can take advantage of graphical wireless application development and visual energy profiling and optimization. The board also serves as an RF reference design for applications targeting 2.4 GHz wireless operation with 20 dBm output power. This document contains a brief introduction and description of the BRD4188B Radio Board features, focusing on the RF sections and performance.

RADIO BOARD FEATURES

• Wireless SoC: EFR32MG24B220F1536IM48
• CPU core: ARM® Cortex®-M33
• Flash memory: 1536 kB
• RAM: 256 kB
• Operation frequency: 2.4 GHz
• Transmit power: 20 dBm
• Two SMA connectors for antenna diversity
• Crystals for LFXO and HFXO: 32.768 kHz and 39 MHz
• 8 Mbit low-power serial flash for over-the-air updates

Introduction

The EFR32 Wireless Gecko Radio Boards provide a development platform (together with the Wireless Starter Kit Mainboard) for the Silicon Labs EFR32 Wireless Gecko Wireless System-on-Chips and serve as reference designs for the matching network of the RF interface. The BRD4188B Radio Board is designed to operate in the 2400-2483.5 MHz band with the RF matching network optimized for operat- ing at 20 dBm output power. To develop and/or evaluate the EFR32 Wireless Gecko, the BRD4188B Radio Board can be connected to the Wireless Starter Kit Mainboard to get access to the debug interface, Virtual COM port, packet trace, display, buttons, LEDs, and additional features from expansion boards, and also to evaluate the performance of the RF interface.

Radio Board Connector

Introduction
The board-to-board connector scheme allows access to all EFR32MG24 GPIO pins as well as the RESETn signal. For more informa-tion on the functions of the available pins, see the EFR32MG24 data sheet.

Radio Board Connector Pin Associations
The figure below shows the mapping between the connector and the EFR32MG24 pins and their function on the Wireless Starter Kit Mainboard.

Radio Board Block Summary

Introduction
This section introduces the blocks of the BRD4188B Radio Board.

Radio Board Block Diagram
The BRD4188B Radio Board block diagram is shown in the figure below.

Radio Board Block Description

Wireless MCU
The BRD4188B Radio Board incorporates an EFR32MG24B220F1536IM48 Wireless System-on-Chip featuring 32-bit Cortex®-M33 core, 1536 kB of flash memory, 256 kB of RAM, and a 2.4 GHz band transceiver with output power up to 20 dBm. For additional infor-mation on the EFR32MG24B220F1536IM48, refer to the EFR32MG24 data sheet.

LF Crystal Oscillator (LFXO)
The BRD4188B Radio Board has a 32.768 kHz crystal mounted. For details regarding the crystal configuration, refer to application note AN0016.2: Oscillator Design Considerations.

HF Crystal Oscillator (HFXO)
The BRD4188B Radio Board has a 39 MHz crystal mounted. For details regarding the crystal configuration, refer to application note AN0016.2: Oscillator Design Considerations.

Matching Network for 2.4 GHz
The BRD4188B Radio Board incorporates a 2.4 GHz matching network which connects the 2.4 GHz RF input/output of the EFR32MG24 to the one on-board printed Inverted-F antenna. The component values were optimized for the 2.4 GHz band RF performance and current consumption with 20 dBm output power. For a detailed description of the matching network, see section 4.2.1 2.4 GHz RF Matching Description.

SMA Connector
To be able to perform conducted measurements or mount external antenna for radiated measurements, range tests, etc., Silicon Labs added two SMA connectors to the radio board. The connector allows external 50 Ohm cables or antennas to be connected during de-sign verification or testing.

Radio Board Connectors
Two dual-row, 0.05” pitch polarized connectors make up the BRD4188B Radio Board interface to the Wireless Starter Kit Mainboard.
For more information on the pin mapping between the EFR32MG24B220F1536IM48 and the connectors, refer to section 2.2 Radio Board Connector Pin Associations.

Serial Flash
The BRD4188B Radio Board is equipped with an 8-Mbit Macronix MX25R SPI flash that is connected directly to the EFR32MG24 to support over-the-air (OTA) updates. For additional information on the pin mapping, see the BRD4188B schematic.

Serial EEPROM
The BRD4188B Radio Board is equipped with a serial I2C EEPROM for board identification and to store additional, board-related information.

RF Section

Introduction
This section gives a short introduction to the RF section of the BRD4188B Radio Board.

RF Section Schematic
BRD4188B Radio Board RF section schematic is shown in the following figure.

GHz RF Matching Description
The 2.4 GHz RF matching connects the 2G4RF1 pin to the onboard, Single-Pole- Double-Through RF switch. The component values were optimized for the 2.4 GHz band RF performance and current consumption with the targeted 20 dBm output power.
The matching network consists of a five-element impedance matching and harmonic filter circuitry and a DC blocking capacitor (not required for the 20 dBm part, but required for the RF switch).
By the RF switch, the matching network output can be connected to either of the two onboard SMA connectors.

Bill of Materials for the 2.4 GHz Matching Network
The bill of materials for the BRD4188B Radio Board 2.4 GHz matching network is shown in the following table.

Table 4.1. Bill of Materials for the BRD4188B 2.4 GHz RF Matching Network

Mechanical Details

The BRD4188B Radio Board is illustrated in the figures below.

EMC Compliance

Introduction
BRD4188B Radio Board fundamental and harmonic levels compliance is tested against the following standards:

• 2.4 GHz:
• ETSI EN 300-328
• FCC 15.247

EMC Regulations for 2.4 GHz

ETSI EN 300-328 Emission Limits for the 2400-2483.5 MHz Band
Based on ETSI EN 300-328, the allowed maximum fundamental power for the 2400-2483.5 MHz band is 20 dBm EIRP. For the unwanted emissions in the 1 GHz to 12.75 GHz domain, the specific limit is -30 dBm EIRP.

FCC15.247 Emission Limits for the 2400-2483.5 MHz Band
FCC 15.247 allows conducted output power up to 1 W (30 dBm) in the 2400-2483.5 MHz band. For spurious emissions, the limit is -20 dBc based on either conducted or radiated measurement, if the emission is not in a restricted band. The restricted bands are speci-fied in FCC 15.205. In these bands, the spurious emission levels must meet the levels set out in FCC 15.209. In the range from 960 MHz to the frequency of the 5th harmonic, it is defined as 0.5 mV/m at 3 m distance, which equals to -41.2 dBm in EIRP.
If operating in the 2400-2483.5 MHz band, the 2nd, 3rd, and 5th harmonics can fall into restricted bands. As a result, for those harmonics the -41.2 dBm limit should be applied. For the 4th harmonic, the -20 dBc limit should be applied.

Applied Emission Limits for the 2.4 GHz Band
The above ETSI limits are applied both for conducted and radiated measurements. The FCC restricted band limits are radiated limits only. In addition, Silicon Labs applies the same restrictions to the conducted spec- trum. By doing so, compliance with the radiated limits can be estimated based on the conducted measurement by assuming the use of an antenna with 0 dB gain at the fundamental and the harmonic frequencies. The overall applied limits are shown in the table below. For the harmonics that fall into the FCC restricted bands, the FCC 15.209 limit is applied. ETSI EN 300-328 limit is applied for the rest.

Table 6.1. Applied Limits for Spurious Emissions for the 2.4 GHz Band

RF Performance

Conducted Power Measurements
During measurements, the BRD4188B Radio Board was attached to a Wireless Starter Kit Mainboard, which was supplied by USB. The voltage supply for the radio board (VMCU) and the power amlifier (PAVDD) was 3.3 V.

Conducted Power Measurements with Unmodulated Carrier
The transceiver was operated in unmodulated carrier transmission mode. The output power of the radio was set to 20 dBm. The typical output spectrum is shown in the following figure.

As shown in the figure, the fundamental is a bit lower than 20 dBm and all of the unwanted emissions are under the -41.2 dBm limit.

Note: The conducted measurement is performed by connecting the onboard UFL connector to a spectrum analyzer through an SMA conversion adapter (P/N: HRMJ-U.FLP(40)). This connection itself introduces approximately 0.3 dB insertion loss.

Conducted Power Measurements with Modulated Carrier
Depending on the applied modulation scheme and the spectrum analyzer settings specified by the relevant EMC regulations, the measured power levels are usually lower compared to the results with an unmodulated carrier. These differences are measured and used as relaxation factors on the results of the radiated measurement performed with an unmodulated carrier. This way, the radiated compliance with modulated transmission can be evaluated. In this case, both the ETSI EN 300-328 and the FCC 15.247 regulations define the following spectrum analyzer settings for measuring unwanted emissions above 1 GHz:

• Detector: Average
• RBW: 1 MHz

The table below shows the measured differences for the supported modulation schemes.

Table 7.1. Measured Relaxation Factors for the Supported Modulation Schemes

Applied Modulation (Packet Length: 255 bytes)| BLE Coded PHY: 125 Kb/s (PRBS9) [dB]| BLE Coded PHY: 500 Kb/s (PRBS9) [dB]| BLE 1M PHY: 1 Mb/s (PRBS9) [dB]| BLE 2M PHY: 2 Mb/s (PRBS9) [dB]
---|---|---|---|---
2nd harmonic| -2.7| -3.1| -3.3| -9.1
3rd harmonic| -4.8| -5.2| -5.2| -10.7
4th harmonic| -5.5| -6.5| -6.7| -11.9
5th harmonic| -6.3| -6.5| -6.7| -11.4

As shown, the BLE 125 Kb/s coded modulation scheme has the lowest relaxation factors. These values will be used as the worst-case relaxation factors for the radiated measurements.

Radiated Power Measurements
During measurements, the BRD4188B Radio Board was attached to a Wireless Starter Kit Mainboard which was supplied by USB. The voltage supply for the radio board was 3.3 V. The radiated power was measured in an antenna chamber by rotating the board 360 degrees with horizontal and vertical reference antenna polarizations in the XY, XZ, and YZ cuts. The measurement planes are illustrated in the figure below.

Note: The radiated measurement results presented in this document were recorded in an unlicensed antenna chamber. Also, the radiated power levels may change depending on the actual application (PCB size, antenna used, and so on). Therefore, the absolute levels and margins of the final application are recommended to be verified in a licensed EMC test house.

Maximum Radiated Power Measurements
During the measurement, bendable whip antennas (P/N: KLS1-WIFI-2.4G-04-MS) were attached to both of the BRD4188B Radio Board SMA connectors. The on-chip DC-DC converter provided 1.8 V power supply for the RF section (RFVDD). For the 2.4 GHz pow-er amplifier (PAVDD), 3.3 V supply was provided by the VMCU line. For details, see the BRD4188B schematic. The transceiver was operated in unmodulated carrier transmission mode. The output power of the radio was set to 20 dBm based on the conducted meas-urement. The orientation of the whip antennas is shown in the figure below. The antenna connected to the right side SMA connector was used as the transmitter antenna.

The results are shown in the tables below. The correction factors are applied based on the BLE 125 Kb/s coded modulation, shown in section 7.1.2 Conducted Power Measurements with Modulated Carrier. For the rest of the supported modulation schemes, the correlation factors are larger, thus the related calculated margins would be higher compared to the ones shown in the table below. Thus, the margins below can be considered as worst-case margins.

Table 7.2. Maximums of the Measured Radiated Powers in EIRP [dBm] and the Calculated Modulated Margins in [dB] with the Wireless Starter Kit Mainboard; PAVDD = 3.3 V

Frequency (2440 MHz)

| ****

Measured Un- modulated EIRP [dBm]

| ****

Orientation

| BLE 125 Kb/s Coded Modulation| ****

Limit in EIRP [dBm]

---|---|---|---|---
Correction Fac- tor [dB]| Calculated Modulated EIRP [dBm]| Modulated Mar- gin [dB]
Fund| 22.5| XZ/H| NA (0 is used)| 22.5| 7.5| 30.0
2nd| -46.7| XZ/V| -2.7| -49.7| -8.2| -41.2
3rd| -40.9| YZ/H| -4.8| -45.7| -4.5| -41.2
4th| -54.3| XZ/V| -5.5| -59.8| -29.8| -30.0
5th| -39.9| XZ/V| -6.3| -46.2| -5.0| -41.2

As shown in the table, with 20 dBm output power, the radiated power of the fundamental is higher than 20 dBm due to the high antenna gain. The 3rd and the 5th harmonics are above the limit with the Wireless Starter Kit Mainboard in case of unmodulated carrier transmission. But with the relaxation of the supported modulation schemes, the margins are 4.5 dB and 5.0 dB, respectively.

EMC Compliance Recommendations

Recommendations for 2.4 GHz ETSI EN 300-328 Compliance
As shown in section 7.2 Radiated Power Measurements, the power of the BRD4188B fundamental with 20 dBm output exceeds the 20 dBm limit of the ETSI EN 300-328 regulation during the radiated power measurement due to the high antenna gain. To be compliant, the fundamental power must be reduced by approximately 2.5 dB. The harmonics are compliant with the relevant limits even with the maximum output power. Although the BRD4188B Radio Board has an option for mounting a shielding can, it is not required for compliance.

Recommendations for 2.4 GHz FCC 15.247 Compliance
As shown in section 7.2 Radiated Power Measurements, the power of the BRD4188B fundamental with 20 dBm output is compliant with the 20 dBm limit of the ETSI EN 300-328 regulation. With the supported modulation schemes, the harmonics are also compliant with the relevant limits. Although the BRD4188B Radio Board has an option for mounting a shielding can, it is not required for compliance.

Board Revision History

The board revision is laser engraved in the Board Info field on the bottom side of the PCB, as outlined in the figure below. The revision printed on the silkscreen is the PCB revision.

Errata

Table 10.1. BRD4188B Radio Board Errata

small keep-out to the ground planes, which intro- duces impedance mismatch, so the output power measured at the SMA con- nector is reduced by approx. 0.5 dB.

Document Revision History

Revision 1.0

May, 2022

• Initial document release.

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Disclaimer
Silicon Labs intends to provide customers with the latest, accurate, and in- depth documentation of all peripherals and modules available for system and software implementers using or intending to use Silicon Labs products. Characterization data, available modules and peripherals, memory sizes and memory addresses refer to each specific device, and “Typical” parameters provided can and do vary in different applications. Application examples described herein are for illustrative purposes only. Silicon Labs reserves the right to make changes without further notice to the product information, specifications, and descriptions herein, and does not give warranties as to the accuracy or completeness of the included information. Without prior notification, Silicon Labs may update product firmware during the manufacturing process for security or reliability reasons. Such changes will not alter the specifications or the performance of the product. Silicon Labs shall have no liability for the consequences of use of the information supplied in this document. This document does not imply or expressly grant any license to design or fabricate any integrated circuits. The products are not designed or authorized to be used within any FDA Class III devices, applications for which FDA premarket approval is required, or Life Support Systems without the specific written consent of Silicon Labs. A “Life Support System” is any product or system intended to support or sustain life and/or health, which, if it fails, can be reasonably expected to result in significant personal injury or death. Silicon Labs products are not designed or authorized for military applications. Silicon Labs products shall under no circumstances be used in weapons of mass destruction including (but not limited to) nuclear, biological, or chemical weapons, or missiles capable of delivering such weapons. Silicon Labs disclaims all express and implied warranties and shall not be responsible or liable for any injuries or damages related to use of a Silicon Labs product in such unauthorized applications.

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References

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