EFR32MG 2.4 GHz 19.5 dBm Radio Board
BRD4154A Reference Manual
The EFR32MG family of Wireless SoCs deliver a high performance, low energy wireless solution integrated into a small form
factor package.
By combining a high performance 2.4 GHz RF transceiver with an energy efficient 32-bit
MCU, the family provides designers the ultimate in flexibility with a family of pin-compatible devices that scale from 128/256 kB of flash and 16/32 kB of RAM. The ultra-low
power operating modes and fast wake-up times of the Silicon Labs energy friendly 32bit MCUs, combined with the low transmit and receive power consumption of the 2.4
GHz radio, result in a solution optimized for battery powered applications.
To develop and/or evaluate the EFR32 Mighty Gecko the BRD4154A Radio Board can
be connected to the Wireless Starter Kit Mainboard to get access to display, buttons and
additional features from Expansion Boards.
The EFR32 Mighty Gecko Radio Boards provide a development platform (together with the Wireless Starter Kit Mainboard) for the
Silicon Labs EFR32 Mighty Gecko Wireless System on Chips and serve as reference designs for the matching network of the RF interface.
The BRD4154A Radio Board is designed to the operate in the 2400-2483.5 MHz band with the RF matching network optimized to operate with 19.5 dBm output power.
To develop and/or evaluate the EFR32 Mighty Gecko the BRD4154A Radio Board can be connected to the Wireless Starter Kit Mainboard to get access to display, buttons and additional features from Expansion Boards and also to evaluate the performance of the RF
interface.
* Connection is not available by default.
Can be enabled through solderable jumpers. See the schematic of the Radio Board.
** Connection is only available through the on-board I/O expander. The associated I/O expander ports are shown in brackets.
BRD4154A Reference Manual
Radio Board Connector
2. Radio Board Connector
2.1 Introduction
The board-to-board connector scheme allows access to all EFR32MG1 GPIO pins as well as the RESETn signal. For more information
on the functions of the available pin functions, we refer you to the EFR32MG1 Datasheet.
2.2 Radio Board Connector Pin Associations
The figure below shows the pin mapping on the connector to the radio pins, to the I/O Expander pins (shown in brackets) and their
function on the Wireless Starter Kit Mainboard.
Figure 2.1. BRD4154A Radio Board Connector Pin Mapping
3. Radio Board Block Summary
Inverted-F
PCB
Antenna
2.4 GHz RF
UFL
Connector
LF
Crystal
32.768k
HF
Crystal
38.4M
Radio
Board
Connectors
8 Mbit
MX25R
Serial Flash
I2C
24AA0024
Serial EEPROM
Matching
Network &
Path
Selection
GPIO
UART
Debug
Packet Trace
AEM
I2C
SPI
SPI
2.4 GHz RF
2.4 GHz RF
EFM8
I/O Expander
I2C
Debug
GPIO
EFR32
EFR32
Wireless SoC
3.1 Introduction
This section gives a short introduction to the blocks of the BRD4154A Radio Board.
3.2 Radio Board Block Diagram
The block diagram of the BRD4154A Radio Board is shown in the figure below.
BRD4154A Reference Manual
Radio Board Block Summary
Figure 3.1. BRD4154A Block Diagram
3.3 Radio Board Block Description
3.3.1 Wireless MCU
The BRD4154A EFR32 Mighty Gecko Radio Board incorporates an EFR32MG1P732F256GM32 Wireless System on Chip featuring
32-bit Cortex-M4 with FPU core, 256 kB + 512 kB of flash memory and 32 kB of RAM and a 2.4 GHz band transceiver with output
power up to 19.5 dBm. For additional information on the EFR32MG1P732F256GM32, refer to the EFR32MG1 Data Sheet.
3.3.2 LF Crystal Oscillator (LFXO)
The BRD4154A Radio Board has a 32.768 kHz crystal mounted.
3.3.3 HF Crystal Oscillator (HFXO)
The BRD4154A Radio Board has a 38.4 MHz crystal mounted.
3.3.4 Matching Network for 2.4 GHz
The BRD4154A Radio Board incorporates a 2.4 GHz matching network which connects the 2.4 GHz TRX pin of the EFR32MG1 to the
one on-board printed Inverted-F antenna. The component values were optimized for the 2.4 GHz band RF performace and current consumption with 19.5 dBm output power.
For detailed description of the matching network see Chapter 4.2.1 Description of the 2.4 GHz RF Matching.
3.3.5 Inverted-F Antenna
The BRD4154A 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 4.5 Inverted-F Antenna.
3.3.6 UFL Connector
To be able to perform conducted measurements Silicon Labs added an 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 measurements
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 Schematic of the RF Matching Network for further details).
3.3.7 Radio Board Connectors
Two dual-row, 0.05” pitch polarized connectors make up the BRD4154A Radio Board interface to the Wireless Starter Kit Mainboard.
For more information on the pin mapping between the EFR32MG1P732F256GM32 and the Radio Board Connector refer to Chapter
2.2 Radio Board Connector Pin Associations.
3.3.8 I/O Expander
Due to the I/O port constraint of the EFR32MG1P732F256GM32 the BRD4154A Radio Board has an EFM8 family MCU mounted as an
I/O port expander to be able to utilize additional Wireless Starter Kit Mainboard features (LEDs, display etc.).
For more information on the pin mapping between the I/O Expander and the Radio Board Connector refer to Chapter 2.2 Radio Board
This section gives a short introduction to the RF section of the BRD4154A.
4.2 Schematic of the RF Matching Network
The schematic of the RF section of the BRD4154A Radio Board is shown in the following figure.
BRD4154A Reference Manual
RF Section
Figure 4.1. Schematic of the RF Section of the BRD4154A
4.2.1 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 BRD4154A board is 19.5 dBm thus 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 (0 Ohm) to the R2 resistor position between the output of the matching and the UFL connector.
4.3 RF Section Power Supply
On the BRD4154A Radio Board the supply pin of the RF Analog Power (RFVDD) is connected directly ot the output of the on-chip DCDC converter while the supply for the 2.4 GHz PA (PAVDD) is provided directly by the mainboard. This way, by default, the DC-DC
converter provides 1.8 V for the RF analog section, the mainboard provides 3.3 V for the PA (for details, see the schematic of the
BRD4154A).
4.4 Bill of Materials for the 2.4 GHz Matching
The Bill of Materials of the 2.4 GHz matching network of the BRD4154A Radio Board is shown in the following table.
Table 4.1. Bill of Materials for the BRD4154A 2.4 GHz 19.5 dBm RF Matching Network
The BRD4154A Radio Board includes an on-board printed Inverted-F Antenna tuned for the 2.4 GHz band. Due to the design restrictions 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 thus
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 better than
-10 dB) for the entire 2.4 GHz band.
Figure 4.2. Impedance and Reflection of the Inverted-F Antenna of the BRD4154A
Compliance of the fundamental and harmonic levels 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 specified 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 Watt (30 dBm) in the 2400-2483.5 MHz band. For spurious emmissions 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 (equals to -41.2 dBm in EIRP).
Additionally, for spurious frequencies above 1 GHz FCC 15.35 allows duty-cycle relaxation to the regulatory limits. For the EmberZNet
PRO the relaxation is 3.6 dB. So practically the -41.2 dBm limit can be modified to -37.6 dBm.
In case of operating in the 2400-2483.5 MHz band the 2nd, 3rd and 5th harmonics can fall into restricted bands so for those the
-37.6 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. Besides that, Silicon Labs applies those to the conducted spectrum i.e. it is assumed that in case of a custom board an antenna is used which has 0 dB gain at the fundamental and the harmonic frequencies. In that
theoretical case, based on the conducted measurement, the compliance with the radiated limits can be estimated.
The overall applied limits are shown in the table below.
Table 6.1. Applied Limits for Spurious Emissions for the 2.4 GHz Band
During measurements the BRD4154A 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.
7.1.1 Conducted Measurements in the 2.4 GHz band
The BRD4154A board was connected directly to a Spectrum Analyzer through its UFL connector (the R1 resistor (0 Ohm) was removed
and a 0 Ohm resistor was soldered to the R2 resistor position). The supply for the radio (RFVDD) was 1.8 V provided by the on-chip
DC-DC converter, the supply for the power amplifier (PAVDD) was 3.3 V provided by the Motherboard (for details, see the schematic of
the BRD4154A). The transceiver was operated in continuous carrier transmission mode. The output power of the radio was set to 19.5
dBm.
The typical output spectrum is shown in the following figure.
Figure 7.1. Typical Output Spectrum of the BRD4154A
As it can be observed the fundamental is slightly lower than 19.5 dBm and the strongest unwanted emission is the double-frequency
harmonic but with its -56.45 dBm level it is under the -37.6 dBm applied limit with large margin.
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 approx. 0.3 dB insertion loss.
During measurements the BRD4154A 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 DUT in 360
degree with horizontal and vertical reference antenna polarizations in the XY, XZ and YZ cuts. The measurement axes are as shown in
the figure below.
Figure 7.2. DUT: Radio Board with the Wireless Starter Kit Mainboard (Illustration)
Note: The radiated measurement results presented in this document were recorded in an unlicensed antenna chamber. Also the radi-
ated power levels may change depending on the actual application (PCB size, used antenna etc.) therefore the absolute levels and
margins of the final application is recommended to be verified in a licensed EMC testhouse!
7.2.1 Radiated Measurements in the 2.4 GHz band
For the transmitter antenna the on-board printed Inverted-F antenna of the BRD4154A board was used (the R1 resistor (0 Ohm) was
mounted). The supply for the radio (RFVDD) was 1.8 V provided by the on-chip DC-DC converter, the supply for the power amplifier
(PAVDD) was 3.3 V provided by the Motherboard (for details, see the schematic of the BRD4154A). The transceiver was operated in
continuous carrier transmission mode. The output power of the radio was set to 19.5 dBm.
The results are shown in the table below.
Table 7.1. Maximums of the Measured Radiated Powers of BRD4154A
2.4 GHzEIRP [dBm]OrientationMargin [dB]Limit in EIRP [dBm]
Fund21.9XZ/H8.830
2nd-42.9XZ/H5.3-37.6
3rd-56.0YZ/H18.4-37.6
4th-50.7YZ/V20.7-30
5th
Noise
*
-/->10-37.6
* Signal level is below the Spectrum Analyzer noise floor.
As it can be observed, thanks to the high gain of the Inverted-F antenna, the level of the fundamental is higher than 19.5 dBm. The
strongest harmonic is the double-frequency one but its level is only -42.9 dBm which is under the -37.6 dBm applied limit by approx. 5
dB.
8.1 Recommendations for 2.4 GHz ETSI EN 300-328 compliance
As it was shown in the previous chapter the radiated power of the fundamental of the BRD4154A EFR32 Mighty Gecko Radio Board
complies with the 20 dBm limit of the ETSI EN 300-328 in case of the conducted measurement but due to the high antenna gain the
radiated power is higher than the limit by approx. 2 dB. In order to comply the output power should be reduced (with different antennas,
depending on the gain of the used antenna, the necessary reduction can be different). The harmonic emissions are under the -30 dBm
limit with margin. Although the BRD4154A Radio Board has an option for mounting a shielding can, that is not required for the compliance.
8.2 Recommendations for 2.4 GHz FCC 15.247 compliance
As it was shown in the previous chapter the radiated power of the fundamental of the BRD4154A EFR32 Mighty Gecko Radio Board
complies with the 30 dBm limit of the FCC 15.247. The harmonic emissions are under the -37.6 dBm applied limit both in case of the
conducted and the radiated measurements. Although the BRD4154A Radio Board has an option for mounting a shielding can, that is
not required for the compliance.
A01Added solder jumpers and pulled buttons in to IO-expander. Updated EFR32 part number.
Note: The silkscreen marking on the board (e.g. PCBxxxx A00) denotes the revision of the PCB. The revision of the actual Radio Board
can be read from the on-board EEPROM.
Table of Contents .............................. 14
Table of Contents15
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