Introduction - ST STM32L4x6 Reference Manual

RM0351
21 Digital filter for sigma delta modulators (DFSDM)
21.1

Introduction

Digital filter for sigma delta modulators (DFSDM) is a high-performance module dedicated to
interface external Σ∆ modulators to a microcontroller. It is featuring up to 8 external digital
serial interfaces (channels) and up to 4 digital filters with flexible Sigma Delta stream digital
processing options to offer up to 24-bit final ADC resolution. DFSDM also features optional
parallel data stream input from microcontrollers memory.
An external Σ∆ modulator provides digital data stream of converted analog values from the
external Σ∆ modulator analog input. This digital data stream is sent into a DFSDM input
channel through a serial interface. DFSDM supports several standards to connect various
Σ∆ modulator outputs: SPI interface and Manchester coded 1-wire interface (both with
adjustable parameters). DFSDM module supports the connection of up to 8 multiplexed
input digital serial channels which are shared with up to 4 DFSDM modules. DFSDM
module also supports alternative parallel data inputs from up to 8 internal 16-bit data
channels (from microcontrollers memory).
DFSDM is converting an input data stream into a final digital data word which represents an
analog input value on a Σ∆ modulator analog input. The conversion is based on a
configurable digital process: the digital filtering and decimation of the input serial data
stream.
The conversion speed and resolution are adjustable according to configurable parameters
for digital processing: filter type, filter order, length of filter, integrator length. The maximum
output data resolution is up to 24 bits. There are two conversion modes: single conversion
mode and continuous mode. The data can be automatically stored in a system RAM buffer
through DMA, thus reducing the software overhead.
A flexible timer triggering system can be used to control the start of conversion of DFSDM.
This timing control is capable of triggering simultaneous conversions or inserting a
programmable delay between conversions.
DFSDM features an analog watchdog function. Analog watchdog can be assigned to any of
the input channel data stream or to final output data. Analog watchdog has its own digital
filtering of input data stream to reach the required speed and resolution of watched data.
To detect short-circuit in control applications, there is a short-circuit detector. This block
watches each input channel data stream for occurrence of stable data for a defined time
duration (several 0's or 1's in an input data stream).
An extremes detector block watches final output data and stores maximum and minimum
values from the output data values. The extremes values stored can be restarted by
software.
Two power modes are supported: normal mode and stop mode.
Digital filter for sigma delta modulators (DFSDM)
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