Application circuit

AN4133

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Doc ID 023362 Rev 1

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Application circuit

Figure 1 shows the SPIRIT1 application board. The application is composed of two boards:

a daughterboard and a motherboard. The daughterboard holds the SPIRIT1 with the circuits

necessary for operation. In order to function properly the daughterboard has to be plugged

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

The motherboard is provided with an 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 the

SPIRIT1.

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

SPIRIT1.

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

SPIRIT1 the best in class for the application 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 the antenna or to the instrumentation

to verify the correct functionality and verify the ETSI standard request.

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

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

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

switch. This daughterboard is designed to show the functionality of the SPIRIT1 in this

condition. Of course an application with antenna switch can be implemented, but this isn't

described in this document.

Figure 1.

SPIRIT1 application daughterboard