Application circuit

AN4117

4/22

Doc ID 023222 Rev 1

1

Application circuit

Figure 1 shows an image of the SPIRIT1 application daughterboard. The application is

made up of two boards: a daughterboard and a motherboard. The daughterboard includes

the SPIRIT1 with the circuits necessary for its functioning. For correct functionality, the

daughterboard must be plugged into a motherboard (see Figure 2) by two header 5x2

connectors (J6 and J7).

The motherboard is provided with an STM32L152VBT6 micro to correctly program the

transceiver. The micro is programmed with a firmware developed for the SPIRIT1

application. A graphical user interface (GUI) has been developed to correctly program the

SPIRIT1.

The daughterboard is provided with a 52 MHz XTAL to provide the correct oscillator to the

SPIRIT1.

The SPIRIT1 has an internal SMPS that drastically reduces power consumption, making it

the best in class for applications on this bandwidth. The SMPS is fed from the battery (1.8 V

to 3.6 V) and provides a programmable voltage (1.4 V typ.) to the device. An SMA connector

is present to connect the board at the antenna or at the instrumentation to verify the correct

functionality and the ETSI standard request.

A few passive parts (inductors and capacitors) are used as matching/filtering for the power

amplifier (PA) and a balun network for the receiver.

To reduce application costs, the SPIRIT1 is designed to work without an external antenna

switch. This daughterboard is designed to show the SPIRIT1 functions in this condition. An

application with an antenna switch can certainly be realized but is not described in this

document.

Figure 1.

SPIRIT1 application daughterboard