nRF21540 FEM configuration with ESB protocol

[Yanis]

Hello all,

I am having issues with the configuration of the FEM nRF21540 on the costum board Fanstel BT840NE with the Enhanced ShockBurst (ESB) protocole.

We are not able to set the PA output TX to a maximum of 20 dBm.

Range tests show that performance decreased compared to our previous chip based on BT840XE (skyworks FEM) set at a TX power of 20 dBm.

We have been testing the esb_ptx and esb_prx examples with the Following configuration in GPIO mode.

prj.conf :

# Enable ESB radio module
CONFIG_ESB=y
CONFIG_ESB_MAX_PAYLOAD_LENGTH=68
CONFIG_ESB_RX_FIFO_SIZE=10
CONFIG_ESB_TX_FIFO_SIZE=50
CONFIG_ESB_NEVER_DISABLE_TX=y
# Enable FEM
CONFIG_MPSL=y
CONFIG_MPSL_FEM=y
CONFIG_MPSL_FEM_NRF21540_GPIO=y
CONFIG_MPSL_FEM_NRF21540_GPIO_SPI=n

We are following the instructions provided :
- "enable the MODE pin in devicetree."
- "The state of the remaining control pins should be set in other ways and according to nRF21540 Product Specification."
So we added the following lines to our main.c source code:

#define NRF21540_NODE DT_NODELABEL(nrf_radio_fem)
static const struct gpio_dt_spec ant_sel_pin = GPIO_DT_SPEC_GET(NRF21540_NODE, ant_sel_gpios);
static const struct gpio_dt_spec mode_pin = GPIO_DT_SPEC_GET(NRF21540_NODE, mode_gpios);
static const struct gpio_dt_spec pdn_pin = GPIO_DT_SPEC_GET(NRF21540_NODE, pdn_gpios);

/* Configure Antenna select pin */
if (!device_is_ready(ant_sel_pin.port))
{
LOG_ERR("Ant_sel init failed (err %d)\n", err);
return 0;
}
gpio_pin_configure_dt(&ant_sel_pin, GPIO_OUTPUT_INACTIVE);
gpio_pin_set_dt(&ant_sel_pin, 1); // Antenna 1

/* Configure Mode select pin */
if (!device_is_ready(mode_pin.port))
{
LOG_ERR("Mode_sel init failed (err %d)\n", err);
return 0;
}
gpio_pin_configure_dt(&mode_pin, GPIO_OUTPUT_INACTIVE);

/* Configure PDN pin */
if (!device_is_ready(pdn_pin.port))
{
LOG_ERR("PDN_sel init failed (err %d)\n", err);
return 0;
}
gpio_pin_configure_dt(&pdn_pin, GPIO_OUTPUT_INACTIVE);

gpio_pin_set_dt(&pdn_pin, 0);
k_msleep(50);
gpio_pin_set_dt(&mode_pin, 0); // POUTA Chip production
// default value used 20 dBm +/- 0.5 dB
k_msleep(50);
gpio_pin_set_dt(&pdn_pin, 1);
k_msleep(50);

Is this the correct way to get 20dB TX gain from the nRF21540 in GPIO mode ?

Thank you in advance for your response,

best regards,

Yanis

[Kenneth]

Hi,

It would help to know what difference you see, e.g. conducted or radiated. Also make sure you have followed the guidelines of the module manufacturer of placement of the module.

Looking at the answer here it should be straight forward:
How to control NRF21540 in ESB

Kenneth

[Yanis]

Hello,

Sorry for the late response, I took time to further investigate.

First of all, I am using SDK 2.7.0.

We are using an external antenna with a ufl connexion cable, so the placement of the module is not that important.

We've tested in radiated using a nRF52840 DK which measures the RSSI of the signal sent by the FEM nRF21540.

I also measured the current consumption of the nRF21540 using the ppk2.

It seems that when I set :

CONFIG_MPSL_FEM_NRF21540_TX_GAIN_DB=10

The RSSI is -26dBm and the current is 65 mA

and when I set :

CONFIG_MPSL_FEM_NRF21540_TX_GAIN_DB=20

The RSSI is -32 dBm and the current is 60 mA

 

The gain at 10 seems to give better performance and more consumption compared to the gain at 20. It is a little confusing.