AN4103

Application circuit

Doc ID 023130 Rev 1

3/20

1

Application circuit

Figure 1 shows the SPIRIT1 application board photo. The application consists of two

boards: a daughterboard and a motherboard. The daughterboard holds SPIRIT1 with the

circuits necessary for its operation. In order to function correctly, the daughterboard must be

plugged into the motherboard (see Figure 2) using two header 5x2 connectors (J6 and J7).

The motherboard is provided with a STM32L152VBT6 microcontroller to correctly program

the transceiver. The microcontroller is programmed with firmware developed for the

SPIRIT1 application. A graphical user interface (GUI) has been developed to correctly

program SPIRIT1.

The daughterboard is provided with a 25 MHz crystal to provide the correct oscillator to

SPIRIT1. The W-MBUS N-mode application, built expressly for the 169 MHz band, needs a

frequency tolerance that cannot be achieved with a quartz oscillator. A dedicated W-MBUS

application at 169 MHz with a range extender to +27 dBm has been developed and it is

described in a dedicated application note for general-purpose applications that work in the

169.400 - 169.475 MHz bandwidth.

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

SPIRIT1 the best-in-class for applications in this bandwidth. The SMPS is fed from the

battery (1.8 V to 3.6 V) and provides a programmable voltage (1.4 V usually) to the device.

An SMA connector is present to connect the board to an antenna or to instruments to verify

the correct functionality and verify the ETSI standard request.

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

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

To reduce the application cost SPIRIT1 has been designed to work without an external

antenna switch. This daughterboard has been designed to show the SPIRIT1 functionality in

this condition. Clearly, an application with an antenna switch can exist, but this case is not

described in this document.