Active GNSS Antenna Supply on EVK-1110-STM

Hardware application note on how to use active GNSS antenna with EVK-1110-STM (DEV-FMLR-STEVK6)

Abstract

Miromico’s Evaluation Kit EVK-1110-STM is using an FMLR-1110-U-STL0Z module that integrates a Semtech LoRa Edge^™ LR1110 chipset featuring passive Wi-Fi AP MAC address scanning and a GNSS (GPS/BeiDou) low-power scanning.

This application note shows the required hardware and firmware steps for GNSS scanning with an active GNSS antenna.

Active vs passive antenna

The LR1110 GNSS scanning can be implemented with both active and passive GNSS antennas. While passive antennas contain only the radiating element, active antennas are additionally equipped with a Low-Noise Amplifier (LNA), which is beneficial for the GPS performance, but adds to the overall power consumption. Compared to passive antennas, active antennas require a power supply on the antenna path.

Note

The use of an active antenna in conjunction with the LR1110 chipset is recommended.

Hardware implementation

As the evaluation kit is shipped with an active GNSS antenna, it provides hardware infrastructure to switch on the required supply for the active antenna using an MCU GPIO in conjunction with a high-side power switch device.

Firmware implementation

The code snippet below shows how to initialize and switch on the supply for the active antenna using the pin PB0 and the STM32L0 HAL library driver:

void gnss_supply_init() {
    // Configure power switch pin
    GPIO_InitTypeDef GPIO_InitStruct = { 0 };

    GPIO_InitStruct.Pin = GPIO_PIN0;
    GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_PP;
    GPIO_InitStruct.Pull = GPIO_NOPULL;
    GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_VERY_HIGH;
    HAL_GPIO_Init(GPIOB, &GPIO_InitStruct);    
}

void gnss_supply_switch(uint8_t enable) {
    HAL_GPIO_WritePin(GPIOB, GPIO_PIN0, enable);
}

Using a passive antenna

If a passive antenna should be used with the EVK-1110-STM where active antenna supply is assembled, it is sufficient to ensure active antenna supply is disabled all the time.