PA/LNA module

The nRF5 SDK for Mesh provides a PA/LNA module with APIs for interfacing the external Front End Modules (FEMs) to increase the range of Bluetooth Low Energy communication.

The FEMs are controlled by the enable signals that turn on a power amplifier (PA) or a low noise amplifier (LNA) (see the following figure). To ensure sufficient ramp-up time, these signals must be activated some time before the start of the radio transmission or reception.

Interfacing PA/LNA with an nRF52 device

The Mesh PA/LNA module enables users to control such external components using GPIOs that are synchronized to the radio operation. The PA/LNA module drives the chosen GPIO pins according to the chosen polarity (Active High/Active Low).

See the following section for an example of how to use the PA/LNA module. You can find more information about the available APIs in the PA/LNA API documentation.

The Mesh PA/LNA module works with all the fully compatible configurations based on nRF52 devices.

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Adding PA/LNA support to the application

This section describes how to add PA/LNA support to the light_switch/server example. For more information about this example, see Light switch example and Light switch server details and Mesh APIs.

To add the PA/LNA support, complete the steps in the following subsections:

• Selecting GPIO pins and PPI channels
• Editing the main.c file
• Running the example and observing the results

Selecting GPIO pins and PPI channels

Complete the following steps:

1. Select the unused GPIO pins that can be used by the PA/LNA module.
   • For this example, use GPIO 25 for controlling the LNA and GPIO 24 for controlling the PA.
   • Also, assume that the control signals required by the external hardware module are Active High. The Mesh PA/LNA module uses the PPI and GPIOTE hardware modules to generate these signals. To read more about these modules in nRF52832, see the following documents: nRF52832 PPI and nRF52832 GPIOTE .
2. Select the unused PPI channels 0 and 1, and the GPIOTE channel 0.

Editing the main.c file

Make the following changes in light_switch/server/src/main.c:

1. Include the required module header file: mesh_pa_lna.h
2. Create a static global variable of type mesh_pa_lna_gpiote_params_t and initialize it with the selected values:

   static mesh_pa_lna_gpiote_params_t m_pa_lna_params = {
    .lna_cfg = {
    .enable = 1,
    .active_high = 1,
    .gpio_pin = 25
    },
    .pa_cfg = {
    .enable = 1,
    .active_high = 1,
    .gpio_pin = 24
    },
    .ppi_ch_id_set = 0,
    .ppi_ch_id_clr = 1,
    .gpiote_ch_id = 0
    };

3. Enable the PA/LNA module by calling mesh_pa_lna_gpiote_enable() after the call to mesh_init():

   mesh_pa_lna_gpiote_enable(&m_pa_lna_params);
   

4. Enable the PA/LNA module in the BLE stack by completing the following steps:
   1. Create a static global variable of type ble_opt_t. You can use the same GPIO pins and the same PPI and GPIO channels as for Mesh PA/LNA configuration:

      static ble_opt_t ble_pa_lna_opts = {
       .common_opt = {
       .pa_lna = {
       .pa_cfg = {
       .enable = 1,
       .active_high = 1,
       .gpio_pin = 24
       },
       .lna_cfg = {
       .enable = 1,
       .active_high = 1,
       .gpio_pin = 25
       },
       .ppi_ch_id_set = 0,
       .ppi_ch_id_clr = 1,
       .gpiote_ch_id = 0
       }
       }
      };

   2. Call sd_ble_opt_set function before the call to mesh_init():

      err_code = sd_ble_opt_set(BLE_COMMON_OPT_PA_LNA, &ble_pa_lna_opts);
      APP_ERROR_CHECK(err_code);

   3. If Mesh examples provisionee support module is used, implement mesh_provisionee_start_params_t::prov_sd_ble_opt_set_cb callback and call sd_ble_opt_set in the callback:

      static void provisioning_sd_ble_opt_cb()
      {
       err_code = sd_ble_opt_set(BLE_COMMON_OPT_PA_LNA, &ble_pa_lna_opts);
       APP_ERROR_CHECK(err_code);
      }
      
      ...
      
      static void start(void)
      {
       rtt_input_enable(app_rtt_input_handler, RTT_INPUT_POLL_PERIOD_MS);
      
       if (!m_device_provisioned)
       {
       static const uint8_t static_auth_data[NRF_MESH_KEY_SIZE] = STATIC_AUTH_DATA;
       mesh_provisionee_start_params_t prov_start_params =
       {
       .p_static_data = static_auth_data,
       .prov_sd_ble_opt_set_cb = provisioning_sd_ble_opt_cb,
       .prov_complete_cb = provisioning_complete_cb,
       .prov_device_identification_start_cb = device_identification_start_cb,
       .prov_device_identification_stop_cb = NULL,
       .prov_abort_cb = provisioning_aborted_cb,
       .p_device_uri = EX_URI_LS_SERVER
       };
       ERROR_CHECK(mesh_provisionee_prov_start(&prov_start_params));
       }
      
       ...
      }

      This is required to restore the PA/LNA configuration in the BLE stack after it is restarted during the provisioning when PB GATT feature is enabled.

Running the example and observing the results

Complete the following steps:

1. Build the example by following the instructions in Building the mesh stack and examples.
2. Run the example by following the instructions in Building the mesh stack and examples for commands required to program a device using `nrfjprog`.

If you connect a logic analyzer to the GPIO pins 25 and 24, you will see them toggling.

The unprovisioned device sends the unprovisioned node beacons every two seconds (NRF_MESH_PROV_BEARER_ADV_UNPROV_BEACON_INTERVAL_MS) and scans for the incoming provisioning invite for the rest of the time.

GPIO waveforms after enabling PA/LNA module

You will see brief Active High pulses on the GPIO pin 24, which is used for the PA control. Similarly, the GPIO pin 25 (used for the LNA control) is almost always ON, except for the time when the radio switches to the next advertising channel for scanning or for sending advertisements.