AN4110

Application circuit

Doc ID 023182 Rev 1

3/18

1

Application circuit

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

made up of 2 boards: a daughterboard and a motherboard. The daughterboard includes the

SPIRIT1 with all the required external components. For correct functioning, the

daughterboard must be plugged into a motherboard (see Figure 2) through 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 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 50 MHz Xtal to provide the correct oscillator to the

SPIRIT. The W-MBUS S-mode, T-mode and R-mode applications, expressly used for the

868 MHz band, can be supported by the SPIRIT. A dedicated W-MBUS application

(firmware) at 868 MHz has been developed. This document is for general purpose

applications that work in the 863.000 - 870.000 MHz bandwidth.

The SPIRIT has an internal SMPS that drastically reduces power consumption, making the

SPIRIT1 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 typically) 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 verify the ETSI standard request.

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

amplifier (PA) and balun network for the receiver.

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

switch. This daughterboard is designed to show the SPIRIT 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