EFR32xG24 2.4 GHz 20 dBm Antenna Diversity Radio Board BRD4188B Reference Manual
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 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
1. 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.
2. 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.
P200 Upper Row: 3V3, JOYSTICK* / PD02* / P36, NC / P38, NC / P40, DBG_TDO_SWO / TRACED0 / PA03 / P42, TRACED2 / PA06 / P44, DBG_TMS_SWDIO / PA02 / F0, DBG_TDO_SWO / TRACED0 / PA03 / F2, DBG_RESET / RESETn / F4, VCOM_TX / PA08 / F6, VCOM_CTS / PB05 / F8, UIF_BUTTON1 / UIF_LED1 / PB02 / F10, UIF_BUTTON0 / UIF_LED0 / PB01 / F12, DISP_ENABLE / PC09 / F14, DISP_SI / PC01 / F16, DISP_EXTCOMIN / PC06 / F18, PTI_DATA / PD04 / F20, USB_VBUS, 5V, Board ID SCL, GND.
P200 Lower Row: P37 / NC, P39 / NC, P41 / PA04 / DBG_TDI / TRACECLK, P43 / PA05 / TRACED1, P45 / PA07 / TRACED3, F1 / PA01 / DBG_TCK_SWCLK, F3 / PA04 / DBG_TDI / TRACECLK, F5 / PB00 / VCOM_ENABLE, F7 / PA09 / VCOM_RX, F9 / PA00 / VCOM_RTS, F11 / PB02 / UIF_BUTTON1 / UIF_LED1, F13 / PB01 / UIF_BUTTON0 / UIF_LED0, F15 / PC03 / DISP_SCLK, F17 / PC08 / DISP_SCS, F19 / PD05 / PTI_SYNC, F21 / NC, USB_VREG, GND, Board ID SDA.
P201 Lower Row: GND, VMCU_IN, P1 / PC01 / DISP_SI, P3 / PC02, P5 / PC03 / DISP_SCLK, P7 / PC00, P9 / PA08 / VCOM_TX, P11 / PA09 / VCOM_RX, P13 / PC07, P15 / PB00 / VCOM_ENABLE, P17 / PB01 / UIF_BUTTON0 / UIF_LED0, P19 / PB02 / UIF_BUTTON1 / UIF_LED1, P21 / NC, P23 / NC, P25 / PD04 / PTI_DATA, P27 / NC, P29 / PC09 / DISP_ENABLE, P31 / PC08 / DISP_SCS, P33 / PC06 / DISP_EXTCOMIN, P35 / PC04, VRF_IN.
P201 Upper Row: VCOM_CTS / PB05 / P0, VCOM_RTS / PA00 / P2, TRACED1 / PA05 / P4, JOYSTICK* / PD02* / P6, TRACED2 / PA06 / P8, TRACED3 / PA07 / P10, PC05 / P12, DBG_TDI / TRACECLK / PA04 / P14, DBG_TDO_SWO / TRACED0 / PA03 / P16, DBG_TMS_SWDIO / PA02 / P18, DBG_TCK_SWCLK / PA01 / P20, NC / P22, PTI_SYNC / PD05 / P24, NC / P26, NC / P28, NC / P30, NC / P32, NC / P34, GND.
*Mutually exclusive connections. Default: PD02 to P6.
The image shows the BRD4188B Radio Board Connector Pin Mapping, detailing the pin assignments for the P200 and P201 connectors.
3. 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 illustrates the interconnected components: Radio Board Connectors, EFR32 Wireless SoC, 2.4 GHz Matching Network, RF Switch, Serial Flash, Serial EEPROM, LF Crystal, HF Crystal, and SMA Connectors. It also shows various interfaces like I2C, GPIO, UART, Debug, AEM, Packet Trace, and SPI connecting to the SoC.
3.3 Radio Board Block Description
3.3.1 Wireless MCU
The BRD4188B Radio Board incorporates an EFR32MG24B220F1536IM48 Wireless System-on-Chip featuring a 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, 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 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 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 that connects the 2.4 GHz RF input/output of the EFR32MG24 to the 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, see section 4.2.1 2.4 GHz RF Matching Description.
3.3.5 SMA Connector
Silicon Labs added two SMA connectors to the radio board to enable conducted measurements or mounting external antennas for radiated measurements, range tests, etc. These connectors allow 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 interface the BRD4188B Radio Board to the Wireless Starter Kit Mainboard. For pin mapping information, 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 connected directly to the EFR32MG24 to support over-the-air (OTA) updates. For pin mapping information, see the BRD4188B schematic.
3.3.8 Serial EEPROM
The BRD4188B Radio Board is equipped with a serial I2C EEPROM for board identification and storing additional, board-related information.
4. 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
The BRD4188B Radio Board RF section schematic is shown in the figure. It depicts the High Frequency Crystal connected to the EFR32MG24's HFXTAL pins. The EFR32MG24's 2G4RF0 pin connects to a 2.4 GHz Matching Network (composed of inductors L1, L2 and capacitors C1, C2, C3, CC1) which then connects to an RF Switch. The RF Switch output is routed to two SMA connectors via CC11 and CC21. Power supply filtering components are also shown.
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.
| 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 |
5. Mechanical Details
The BRD4188B Radio Board is illustrated in the figures below.
Top View: The top view shows the physical layout of components on the board, including the EFR32xG24, DCDC Inductor, DCDC & Supply Filter Caps, LFXTAL, HFXTAL, OTA Flash, RFVDD Supply Filtering, 2.4 GHz Matching Network, and two SMA Connectors. Dimensions are approximately 45mm width and 30mm height, with space for an optional shielding can.
Bottom View: The bottom view shows the interface connectors (P200, P201), Board Identification area, PD02 to Exp Header or Joystick Selection, and PAVDD Supply Selection. Dimensions are approximately 24mm width and 28.6mm height.
6. 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 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 (if not in a restricted band) or -41.2 dBm in EIRP for emissions in restricted bands (e.g., 960 MHz to the 5th harmonic). For the 4th harmonic, the -20 dBc limit applies.
6.2.3 Applied Emission Limits for the 2.4 GHz Band
The ETSI limits are applied for both conducted and radiated measurements. FCC restricted band limits are radiated limits, but Silicon Labs applies them to the conducted spectrum as well. This allows estimating radiated compliance from conducted measurements by assuming 0 dB antenna gain.
The overall applied limits for spurious emissions are shown in the table below. For harmonics in FCC restricted bands, the FCC 15.209 limit is applied; otherwise, the ETSI EN 300-328 limit is applied.
| 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 |
7. RF Performance
7.1 Conducted Power Measurements
7.1.1 Conducted Power Measurements with Unmodulated Carrier
During measurements, the BRD4188B Radio Board was attached to a Wireless Starter Kit Mainboard, supplied by USB. The voltage supply for the radio board (VMCU) and the power amplifier (PAVDD) was 3.3 V. The transceiver was operated in unmodulated carrier transmission mode with the output power set to 20 dBm. The typical output spectrum is shown in the figure. The fundamental is slightly lower than 20 dBm, and all unwanted emissions are under the -41.2 dBm limit.
Note: The conducted measurement uses an SMA conversion adapter, which introduces approximately 0.3 dB insertion loss.
7.1.2 Conducted Power Measurements with Modulated Carrier
Measured power levels are typically lower with modulated carriers compared to unmodulated carriers. These differences serve as relaxation factors for radiated measurement compliance evaluation. Spectrum analyzer settings for measuring unwanted emissions above 1 GHz include Detector: Average and RBW: 1 MHz.
The table shows measured differences (relaxation factors) for 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 |
The BLE 125 Kb/s coded modulation scheme has the lowest relaxation factors, used as worst-case values for radiated measurements.
7.2 Radiated Power Measurements
During measurements, the BRD4188B Radio Board was attached to a Wireless Starter Kit Mainboard (3.3 V supply). Radiated power was measured in an antenna chamber by rotating the board 360 degrees with horizontal and vertical antenna polarizations in XY, XZ, and YZ cuts. The measurement planes are illustrated in the figure.
The figure illustrates the X, Y, and Z axes relative to the radio board for measurement purposes.
Note: Results were recorded in an unlicensed antenna chamber. Radiated power levels may vary with the application (PCB size, antenna). Verification in a licensed EMC testhouse is recommended for final applications.
7.2.1 Maximum Radiated Power Measurements
Bendable whip antennas were attached to the BRD4188B SMA connectors. The on-chip DC-DC converter supplied 1.8 V for RFVDD, and the VMCU line supplied 3.3 V for PAVDD. The transceiver operated in unmodulated carrier mode at 20 dBm output power.
The figure shows the orientation of the whip antennas, with the right-side SMA connector antenna used as the transmitter antenna.
The results are presented in the tables below. Correction factors are based on BLE 125 Kb/s coded modulation. The table shows measured radiated powers and calculated modulated margins.
| Frequency (2440 MHz) | Measured Unmodulated EIRP [dBm] | Orientation | Correction Factor [dB] | Calculated Modulated EIRP [dBm] | Modulated Margin [dB] | Limit in EIRP [dBm] |
|---|---|---|---|---|---|---|
| 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 |
With 20 dBm output power, the fundamental radiated power is higher than 20 dBm due to antenna gain. The 3rd and 5th harmonics are above the limit with unmodulated carrier transmission, but with modulation scheme relaxation, margins are 4.5 dB and 5.0 dB, respectively.
8. 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 fundamental power of the BRD4188B with 20 dBm output exceeds the ETSI EN 300-328 20 dBm limit due to high antenna gain. To be compliant, the fundamental power must be reduced by approximately 2.5 dB. Harmonics are compliant with relevant limits even at maximum output power. A shielding can is optional and 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 fundamental power of the BRD4188B with 20 dBm output is compliant with the 20 dBm limit. With supported modulation schemes, harmonics are also compliant. A shielding can is optional and not required for compliance.
9. Board Revision History
The board revision is laser engraved in the Board Info field on the bottom side of the PCB. The figure shows the location of the revision engraving.
| Board Revision | Description |
|---|---|
| A01 | U1 with new factory calibrations, C3 mounted. |
| A00 | Initial release |
10. Errata
The following errata have been identified for the BRD4188B Radio Board.
| 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, reducing the output power measured at the SMA connector by approximately 0.5 dB. |
11. Document Revision History
Revision 1.0
May, 2022
Initial document release.
Disclaimer and Trademark Information
Silicon Labs provides documentation for system and software implementers. Characterization data and parameters may vary. Application examples are for illustration only. Silicon Labs reserves the right to make changes without notice and does not warrant accuracy or completeness. Silicon Labs may update product firmware without altering specifications. Silicon Labs is not liable for consequences of using this information. This document does not grant licenses for integrated circuits. Products are not authorized for FDA Class III devices, applications requiring FDA premarket approval, or Life Support Systems without written consent. Silicon Labs products are not authorized for military applications or weapons of mass destruction. Silicon Labs disclaims all warranties and liability for damages related to unauthorized applications.
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