Ideally, it is assumed that the source (generator) and load has 50Ω impedance, thus to transmit a signal from source to load without any losses, the transmission medium also must have 50Ω impedance.

Practically, the source / load impedance solely cannot be guaranteed to be 50Ω, hence additional impedance matching network is required in the circuit. Matching the impedance of complete RF path will make sure that there is minimum reflection loss and thus the antenna will resonate all of the incoming energy at its resonant frequency.

The RF path of EFR32 Series 1 can be divided into 3 parts as follows:

a) EFR32 Matching Network:

After performing load pull experiments, the optimum termination impedance of power amplifier was found as:

Case A: [Tx power level < +10dBm] ----> 20+j10Ω

Case B: [+20dBm > Tx power level > +10dBm] ----> 23+j11.5Ω

This impedance at the power amplifier should be matched to 50Ω to achieve the maximum power transfer from EFR to antenna. A low pass filter is used to transform this impedance and reject unwanted signals.

For case A, 2 element ladder LC low pass filter is enough to transform the impedance from 20+j10Ω to 50Ω. As max Tx power is limited to +10dBm, additional filtering is not required.
For case B, At higher Tx power, 2nd and 3rd order harmonics go beyond the allowable limit by the regulatory bodies. Hence suppressing higher order harmonics becomes important. To suppress these harmonics, a 3 element Pi filter is combined with the 2 element LC match which then results in a 4 element LCLC ladder that acts as a matching network and a low pass filter.

(For component values, detailed analysis and other types of EFR matching networks, Please refer AN930 rev 0.4 or later).

Thus the impedance at the end of EFR matching network in either case has been successfully transformed to ~50Ω.

b) Pigtail connection (Optional):

Even though pigtail connection is optional, we always recommend everyone to keep a provision for a U.FL connector and a series zero Ω resistor in their prototype design, this will allow the engineer to perform some RF tests such as measuring reflection loss, perform conducted test and etc.

This section is divided into 2 subsections:

i) U.FL connector:

To perform RF conducted test, a provision for U.FL connector can be helpful in the circuit. For this the series zero Ω resistor (3 - Res) has to be removed and it has to be placed at branched path towards U.FL connector. This will help us to ensure that the signal sent by the EFR RFIC is equal to the received signal at U.FL connector. Conducted test helps the engineer to verify that there are no reflection losses in the RF path between EFR and pigtail connection.

ii) Pigtail connector:

To measure reflection loss between pigtail connection and antenna, a pigtail connector is used. This can be done by removing zero Ω resistor (3 – Res) and soldering a pigtail connector at the second pad of the removed component. Please make sure that the metal jacket of the pigtail connector is properly soldered to ground pour from the pad till the edge of the board. By measuring the reflection coefficient, the antenna can also be matched to 50 Ω impedance.

This pigtail connection does not include any kind of impedance transformation, thus the impedance at the end of this network and before antenna is ~50Ω.

c) Antenna Matching Network:

The impedance of the antenna also solely cannot be guaranteed to be 50Ω, hence an additional matching network is required. We usually recommend a 3 element pi structured filter irrespective of the antenna type. Using a pigtail connector would be the starting stage of the antenna matching exercise. More information on the antenna matching network can be found at this KBA.

Please note that detailed design procedure and antenna tuning information for inverted F PCB antenna is given in AN1088.

Within our EmberZNet and Silicon Labs Thread stacks we provide a number of pre-built NCP images.  However, with the customability EFR32 Mighty Gecko, these NCP images don't always meet every application.  This guide, along with reading AN1010: Building a Customized NCP Application, should give you the tools to build your own xNCP image.

1. Go to File -> New -> Project. This will bring up the New Project Wizard
2. Select “Silicon Labs AppBuilder Project”. Click Next.
3. Select “Customizable network coprocessor (NCP) application”. Click Next.
4. Select the Stack you want to use. Click Next.
5. Select xNCP LED. Click Next.
6. Give your project a name, leave it in the default location. Click Next.
7. On the Project Setup Window remove any boards that are selected in the top section.  In the bottom section select the chip you are using. Hit Finish.
8. Download the board header below for your particular stack and copy it into your project (you can drag and drop it into your Project in Studio, when prompted, make sure to Copy the file into your project).
   EmberZNet 5.9.2 and prior: xNCP_board.h
   EmberZNet 5.10.0 and later: xNCP_board_5.10.x.h
9. On the General Tab
   • Selected Architecture – verify the chip you selected is there
10. On the HAL Tab
    • Change Board Header from Default to Use Custom Board Header
    • Point the Custom Board Header to file you downloaded in step 8 (it should be in your Studio v4 Workspace)
11. On the Plugins Tab
    • In the Core section pick the Plug for either NCP-SPI or NCP-UART for the NCP version you are using
    • If you are building a Smart Energy NCP, you will need to enable the CBKE and ECC plugins required for your build.
12. On the Other Tab
    • • (EmberZNet 5.9.2 and prior only) In the Additional .c and .h files section Add the following directories:

    <PATH_TO_STACK_FOLDER_ROOT>\hardware\kit\EFR32MG1_BRD4151A\config
    <PATH_TO_STACK_FOLDER_ROOT>\hardware\kit\common\bsp

13. Open the board header file from step 8 and make these changes:
    • (EmberZNet 5.9.2 and prior)
      •  Find the #define statements for which build to use

        #define UART_XNCP_BUILD
        #define SPI_XNCP_BUILD

        Comment out the one you aren’t using and make sure the one you need is defined
      • Modify the section to match the interface you have selected.  For UART, setup the Tx, Rx, CTS and RTS pins.  For SPI, setup MOSI, MISO, CS and CLK as well as the nHOST, nWAKE and nSSEL (CS) pins.
        See below for where to find ROUTELOC definitions to match these pins.
    • (EmberZNet 5.10.x)
      • If you are building a UART NCP, edit the section titled /* USART0 */.  Setup Tx, Rx, CTS and RTS pins that you are using for your NCP.
        See below for where to find ROUTELOC definitions to match these pins.
      • If you are building a SPI NCP, edit the section titled /* USART1 */.  Setup the MOSI, MISO, CS and CLK pins.
        Additonally, edit the section titled /* SPINCP */.  You shouldn't have to change the USART port, but match the nHOST and nWAKE pins to your design.
        See below for where to find ROUTELOC definitions to match these pins.
    • You can get the ROUTELOC definitions from the Mighty Gecko datasheet corresponding to your model of Mighty Gecko (MG1, MG12 or MG13).  Links to the datasheets are below.
    • Once the modifications are made, save the file
14. Generate the files for your project
15. Build your project

 Use the following KBA for building a bootloader:

Make customized ZigBee bootloader for the EFR32MG1 QFN32 parts
 

 Additional Information:

AN1010: Building a Customized NCP Application

EFR32MG1 Mighty Gecko ZigBee & Thread SoC Family Data Sheet (Section 6.4)

EFR32MG12 Mighty Gecko Multi-Protocol Wireless SoC Family Data Sheet (Section 6.4)

EFR32MG13 Mighty Gecko Multi-Protocol Wireless SoC Family Data Sheet (Section 6.6)