SILICON LABS EFR32BG Wireless Software Adds Bluetooth Connectivity User Guide
- June 3, 2024
- SILICON LABS
Table of Contents
EFR32BG Wireless Software Adds Bluetooth Connectivity
User Guide
Adds Bluetooth Connectivity
The EFR32BG 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 Blue Gecko, the EFR32BG Radio Board can be connected to the
Wireless Starter Kit Mainboard to get access to display, buttons and
additional features from Expansion Boards.
RADIO BOARD FEATURES
- Wireless SoC: EFR32BG1P232F256GM48
- CPU core: ARM Cortex-M4 with FPU
- Flash memory: 256 kB
- RAM: 32 kB
- Operation frequency: 2.4 GHz
- Transmit power: 10.5 dBm
- Integrated PCB antenna, UFL connector (optional).
- Crystals for LFXO and HFXO: 32.768 kHz and 38.4 MHz.
Introduction
The EFR32 Blue Gecko Radio Boards provide a development platform (together
with the Wireless Starter Kit Mainboard) for the Silicon Labs EFR32 Blue Gecko
Wireless System on Chips and serve as reference designs for the matching
network of the RF interface.
The BRD4100A Radio Board is designed to operate in the 2400-2483.5 MHz band
with the RF matching network optimized to operate with 10.5 dBm output power.
To develop and/or evaluate the EFR32 Blue Gecko, the BRD4100A 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.
Radio Board Connector
2.1 Introduction
The board-to-board connector scheme allows access to all EFR32BG1 GPIO pins as
well as the RESETn signal. For more information on the functions of the
available pin functions, see the EFR32BG1 data sheet.
2.2 Radio Board Connector Pin Associations
The figure below shows the pin mapping on the connector to the radio pins and
their function on the Wireless Starter Kit Mainboard.
Radio Board Block Summary
3.1 Introduction
This section gives a short introduction to the blocks of the BRD4100A Radio
Board.
3.2 Radio Board Block Diagram
The block diagram of the EFR32BG Radio Board is shown in the figure below.
3.3 Radio Board Block Description
3.3.1 Wireless MCU
The BRD4100A EFR32 Blue Gecko Radio Board incorporates an EFR32BG1P232F256GM48
Wireless System on Chip featuring 32-bit Cortex-M4 with FPU core, 256 kB f
flash memory and 32 kB of RAM and a 2.4 GHz band transceiver with output power
up to 10.5 dBm. For additional information on the EFR32BG1P232F256GM48, refer
to the EFR32BG1 Data Sheet.
3.3.2 LF Crystal Oscillator (LFXO)
The BRD4100A Radio Board has a 32.768 kHz crystal mounted.
3.3.3 HF Crystal Oscillator (HFXO)
The BRD4100A Radio Board has a 38.4 MHz crystal mounted.
3.3.4 Matching Network for 2.4 GHz
The BRD4100A Radio Board incorporates a 2.4 GHz matching network which
connects the 2.4 GHz TRX pin of the EFR32BG1 to the one on-board printed
Inverted-F ntenna. The component values were optimized for the 2.4 GHz band
RF performace and current consumption with 10.5 dBm output power. For detailed
description of the atching network, see Chapter 4.2.1 Description of the 2.4
GHz RF Matching.
3.3.5 Inverted-F Antenna
The BRD4100A 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 onnected 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. t an 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 EFR32BG Radio Board
interface to the Wireless Starter Kit Mainboard.
For more information on the pin mapping between the EFR32BG1P232F256GM48 and
the Radio Board Connector, refer to Chapter 2.2 Radio Board Connector Pin
ssociations.
RF Section
4.1 Introduction
This section gives a short introduction to the RF section of the BRD4100A.
4.2 Schematic of the RF Matching Network
The schematic of the RF section of the BRD4100A Radio Board is shown in the
following figure.
4.2.1 Description of the 2.4 GHz RF Matching
The 2.4 GHz matching connects the RFIO_P pin to the on-board printed
Inverted-F Antenna. The RFIO_N pin is connected to ground. For lower output
powers (under 13 Bm) additional harmonic filtering is not required as the
harmonic levels are below the regulation limits (see Chapter 7.1.1 Conducted
Measurements in the 2.4 GHz band). herefore, the matching network comprises
only a two-element impedance matching circuitry. The targeted output power is
10.5 dBm. For or conducted easurements he output of the matching network can
also be connected to the UFL connector by removing the series L2 inductor
between the antenna and the output of the matching and adding a 0 Ohm resistor
to the R2 resistor position between the output of the matching and the UFL
connector.
4.3 RF Section Power Supply
On the BRD4100A Radio Board the power supply pins of the RF section (RFVDD,
PAVDD) are directly connected to the output of the on-chip DC-DC converter.
This ay, y default, the DC-DC converter provides 1.8 V for the entire RF
section (for details, see the schematic of the BRD4100A).
4.4 Bill of Materials for the 2.4 GHz Matching
The Bill of Materials of the 2.4 GHz matching network of the BRD4100A Radio
Board is shown in the following table.
Table 4.1. Bill of Materials for the BRD4100A 2.4 GHz 10.5 dBm RF Matching
Network
| Component name | Value | Manufacturer | Part Number |
|---|---|---|---|
| C1 | 1.5 pF | Murata | GRM1555C1H1R05WA01 |
| L1 | 1.9 nH | Murata | LQP15MN1N9W02 |
4.5 Inverted-F Antenna
The BRD4100A 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. As a result, a 50 Ohm transmission line
was necessary to connect them. With the actual line length the impedance of
the antenna at the double-harmonic frequency is transformed closer to a
“critical load impedance range” resulting in the radiated level of the
harmonic increases.
To reduce the harmonic radiation a tuning component was used instead of a
series 0 Ohm resistor between the matching network output and the antenna
input. For the actual Radio Board design (with the actual transmission line
length) a small value inductor was used (L2 inductor with value of 1.9 nH) to
transform the impedance at the double-frequency harmonic away from the
critical region while keeping the impedance at the funamental close to 50 Ohm.
With this the suppression of the radiated double-frequency harmonic increases
by approximately 12 dB. The resulting impedance is shown in the following
figure.
Figure 4.2. Impedance and Reflection of the Inverted-F Antenna of the BRD4100A
Board Measured from the Matching Output
Note: The suppression of the double-frequency harmonic can be further
increased by using a sligthly higher inductor value but for the current board
the suppression chieved with 1.9 nH is sufficient (see Chapter 7.2.1 Radiated
Measurements in the 2.4 GHz band). Therefore, for BOM cost reduction the same
value and type of inductor as used as the one in the matching network.
Mechanical Details
The BRD4100A EFR32 Blue Gecko Radio Board is illustrated in the figures below:
EMC Compliance
6.1 Introduction
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.
herefore, the -41.2 dBm limit can be modified to -37.6 dBm. If operating in
the 2400-2483.5 MHz band the 2nd, 3rd and 5th harmonics can fall into
restricted bands. As a esult, 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, n ntenna 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 he 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
| Harmonic | Frequency | Limit |
|---|---|---|
| 2nd | 4800~4967 MHz | -37.6 dBm |
| 3rd | 7200~7450.5 MHz | -37.6 dBm |
| 4th | 9600~9934 MHz | -30 dBm |
| 5th | 12000~12417.5 MHz | -37.6 dBm |
RF Performance
7.1 Conducted Power Measurements
During measurements, the EFR32BG 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 BRD4100A board was connected directly to a Spectrum Analyzer through its
UFL connector (the L2 inductor was removed and a 0 Ohm resistor was soldered
to the 2 esistor position). During measurements, the voltage supply for the
board was 3.3 V provided by the mainboard. The supply for the RF section was
1.8 V provided by the n-chip DC-DC converter (for details, see the schematic
of the BRD4100A). The transceiver was operated in continuous carrier
transmission mode. The output power of the adio was set to 10.5 dBm. The
typical output spectrum is shown in the following figure.
As it can be observed, the fundamental is slightly lower than 10.5 dBm limit
and the strongest unwanted emission is the double-frequency harmonic and it is
under the -37.6 dBm applied 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.
7.2 Radiated Power Measurements
During measurements, the EFR32BG Radio Board was attached to a Wireless
Starter Kit Mainboard which was supplied by USB. The voltage supply for the
Radio Board was .3 V. The radiated power was measured in an antenna chamber
by rotating the DUT 360 degrees with horizontal and vertical reference antenna
polarizations in the XY, Z and YZ cuts. The measurement axes are shown 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, used antenna, 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 Radiated Measurements in the 2.4 GHz band
For the transmitter antenna the on-board printed Inverted-F antenna of the
BRD4100A board was used (the L2 inductor was mounted). During measurements,
the board was attached to a Wireless Starter Kit Mainboard (BRD4001 (Rev. A02)
) which was supplied through USB. During the measurements the voltage supply
for the board was 3.3 V provided by the mainboard. The supply for the RF
section was 1.8 V provided by the on-chip DC-DC converter (for details, see
the schematic of the BRD4100A). The transceiver was operated in continuous
carrier transmission mode. The output power of the radio was set to 10.5 dBm
based on the conducted measurement. The results are shown in the table below.
Table 7.1. Maximums of the Measured Radiated Powers of BRD4100A
2.4 GHz| EIRP [dBm]| Orientation| Margin [dB]| Limit in
EIRP [dBm]
---|---|---|---|---
Fund| 13.6| YZ/V| 9:36| 30
2nd| -51.5| XZ/H| 13.9| -37.6
3rd| Noise| -/-| >10| -37.6
4th| Noise| -/-| >20| -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 +10.5 dBm. The strongest harmonic is the double- requency one and thanks to the additional suppression provided by the L2 inductor its level is only around -50 dBm.
EMC Compliance Recommendations
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 BRD4100A EFR32 Blue Gecko Radio Board complies with the 20 dBm limit of
the TSI EN 300-328 both in case of the conducted and the radiated
measurements. The harmonic emissions are under the -30 dBm limit. Although the
BRD4100A Radio Board as an option for mounting a shielding can, that is
notrequired 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 BRD4100A EFR32 Blue Gecko Radio Board complies with the 30 dBm limit of
the CC 15.247. The harmonic emissions are under the -37.6 dBm applied limit
both in case of conducted and the radiated measurements. Although the BRD4100A
Radio Board as an option for mounting a shielding can, that not required for
the compliance.
Board Revisions
| Radio Board Revision | Description |
|---|---|
| B01 | Initial release. |
| B02 | Updated EFR32 to revision C0. |
Document Revision History
Revision 1.6
2016-11-20
Minor editorial updates. Fixed missing reference on page 4.
Revision 1.5
2016-10-31
Corrected error in radio board connector pinout diagram.
Revision 1.4
2016-05-24
Updating Board Revisions content.
Revision 1.3
2016-05-05
Adding Introduction chapter; moving SoC Description chapter (short ver.) to
Block Description chapter. Minor improvements.
Revision 1.2
2016-02-11
Adding RF Section Power Supply chapter. Minor improvements.
Revision 1.1
2016-01-28
Fixing image render problem. Replacing DUT refplanes image.
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References
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