SILABS LABS BRD4188B EFR32xG24 2.4 GHz 20 dBm Antenna Diversity Radio Board User Manual
- June 3, 2024
- SILABS LABS
Table of Contents
- BRD4188B EFR32xG24 2.4 GHz 20 dBm Antenna Diversity Radio Board
- Introduction
- Radio Board Connector
- Radio Board Block Summary
- RF Section
- Mechanical Details
- EMC Compliance
- RF Performance
- EMC Compliance Recommendations
- Board Revision History
- Errata
- Document Revision History
- References
- Read User Manual Online (PDF format)
- Download This Manual (PDF format)
EFR32xG24 2.4 GHz 20 dBm Antenna
Diversity Radio Board
BRD4188B Reference Manual
BRD4188B EFR32xG24 2.4 GHz 20 dBm Antenna Diversity Radio Board
The BRD4188B Radio Board enables developers to develop smart home, 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 on-
board 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® -M33
- Flash memory: 1536 kB
- RAM: 256 kB® Cortex
- 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-theair 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 operating 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
2.1 Introduction
The board-to-board connector scheme allows access to all EFR32MG24 GPIO pins
as well as the RESETn signal. For more information on the functions of the
available pins, see the EFR32MG24 data sheet.
2.2 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
3.1 Introduction
This section introduces the blocks of the BRD4188B Radio Board.
3.2 Radio Board Block Diagram
The BRD4188B Radio Board block diagram is shown in the figure below.
3.3 Radio Board Block Description
3.3.1 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 information on the EFR32MG24B220F1536IM48, refer to the EFR32MG24
data sheet.
3.3.2 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.
3.3.3 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.
3.3.4 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.
3.3.5 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 design verification or testing.
3.3.6 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.
3.3.7 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.
3.3.8 Serial EEPROM
The BRD4188B Radio Board is equipped with a serial IC EEPROM for board
identification and to store additional, board-related information.
RF Section
4.1 Introduction
This section gives a short introduction to the RF section of the BRD4188B
Radio Board.
4.2 RF Section Schematic
BRD4188B Radio Board RF section schematic is shown in the following figure.
4.2.1 2.4 GHz RF Matching Description
The 2.4 GHz RF matching connects the 2G4RF1 pin to the on-board, 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 on-board SMA connectors.
4.3 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
| Component Name | Value | Manufacturer | Part Number |
|---|---|---|---|
| L1 | 2.9 nH | Murata | LQP03HQ2N9B02D |
| L2 | 1.2 nH | Murata | LQP03HQ1N2W02D |
| C1 | 2.3 pF | Murata | GRM0335C1H2R3WA01D |
| C2 | 1.6 pF | Murata | GRM0335C1H1R6WA01D |
| C3 | 0.3 pF | Murata | GRM0335C1HR30WA01D |
| CC1 | 18 pF | Murata | GJM0335C1E180GB01D |
Mechanical Details
The BRD4188B Radio Board is illustrated in the figures below.
EMC Compliance
6.1 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
6.2 EMC Regulations for 2.4 GHz
6.2.1 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.
6.2.2 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 specified 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.
6.2.3 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 spectrum.
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. Forthe 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
| Harmonic | Frequency | Limit |
|---|---|---|
| 2nd | 4800~4967 MHz | -41.2 dBm |
| 3rd | 7200~7450.5 MHz | -41.2 dBm |
| 4th | 9600~9934 MHz | -30.0 dBm |
| 5th | 12000~12417.5 MHz | -41.2 dBm |
RF Performance
7.1 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.
7.1.1 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 on-board
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.
7.1.2 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 unmodulated carrier. These
differences are measured and used as relaxation factors on the results of the
radiated measurement performed with 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 the 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 relaxarion factors for
the radiated measurements.
7.2 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 testhouse.
7.2.1 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 power 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 measurement. 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 correction 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 Factor [dB]| Calculated
Modulated EIRP
[dBm]| Modulated Mar-
gin [dB]
Fund| 23.| XZ/H| NA (0 is used)| 23.| 8.| 30.0
2nd| -47.| XZN| -3.| -50.| -8.| -41.
3rd| -41.| YZ/H| -5.| -46.| -5.| -41.
4th| -54.| XZN| -6.| -60.| -30.| –30.0
5th| -40.| XZN| -6.| -46.| –5.0| -41.
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 the 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
8.1 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.
8.2 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.
| Board Revision | Description |
|---|---|
| A01 | U1 with new factory calibrations, C3 mounted. |
| A00 | Initial release |
Errata
Table 10.1. BRD4188B Radio Board Errata
| Board Revision | Problem | Description |
|---|---|---|
| A00-A01 | Slightly reduced fundamental | |
| power. | The SMA connector pin has a small keep-out to the ground planes, which |
introduces impedance mismatch, so the output power measured at the SMA connector is reduced by approx. 0.5 dB.
Document Revision History
Revision 1.0
May, 2022
• Initial document release.
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References
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