Decimation of Delta-Sigma-Modulated Signals Using a Low-Cost Microcontroller

ΔΣ analog-to-digital converters (ADCs) are largely used in sensor acquisition applications. In the last few years, standalone ΔΣ modulators have become increasingly available as off-the-shelf parts. To build a complete ADC, a standalone modulator has to be paired with some advanced elaboration unit, such as a field programmable gate array (FPGA) or a digital signal processor (DSP), which is needed for the implementation of the decimation filter. This work investigates the use of low-cost, general-purpose microcontrollers for the decimation of ΔΣ-modulated signals. The main challenge is given by the clock frequency of the modulator, which can be in the range of a few MHz. The proposed technique deals with this limitation by employing two serial peripheral interface (SPI) modules in a time-interleaved configuration. This approach allows for continuous acquisition and elaboration of relatively high-speed, digital signals. The technique has been applied to a case study, and a data conversion system has been practically realized. The performance of the proposed filter is compared to that of a digital filter, present on board a commercial microcontroller, and the results of experimental tests are provided.