69 Decimation Filter for Incremental and Regular Delta-Sigma Modulators

69 : Decimation Filter for Incremental and Regular Delta-Sigma Modulators

Design render
  • Author: Andrea Murillo Martinez & Jaeden Chang
  • Description: Decimation filter that efficiently reduces oversampled data from incremental and regular delta-sigma modulators, while preserving signal accuaracy.
  • GitHub repository
  • Open in 3D viewer
  • Clock: 50000000 Hz

Overview

The decimation filter efficiently reduces the sample frequency of Incremental and Regular Delta-Sigma Modulators (DSMs) by a factor of 16. This process minimizes high-frequency noise and downsamples data, supporting effective and accurate signal processing of oversampled ADC outputs.

Specifications

  • Inputs: 3 total
    • Input 1 (1 bit): ADC data input
    • Input 2 (1 bit): Decimation mode selection (0 = Incremental DSM, 1 = Regular DSM)
    • Input 3 (1 bit): Global reset
  • Output: 16 bits total
    • Most Significant 8 bits (MSBs): Routed to dedicated output pins
    • Least Significant 8 bits (LSBs): Routed to general-purpose IO pins
  • Clock Frequency: 50 MHz (standard operation)

Mode Selection

The decimation mode can be configured based on the DSM type:

  • Incremental DSM: Set Input 2 to low.
  • Regular DSM: Set Input 2 to high.

How It Works

  1. Noise Reduction and Downsampling: The decimation filter reduces high-frequency quantization noise from DSM oversampling, delivering a downsampled output with preserved signal quality.
  2. Adaptive Output Rate:
    • Incremental DSM (Input 2 Low): The output updates after accumulating 16 input samples.
    • Regular DSM (Input 2 High): The output updates based on an internal timing controlled by the reset signal.
  3. Output Simplification: The filter converts a high data rate from the oversampled ADC into a manageable downsampled rate, optimizing data processing.

Operation

The decimation filter requires an initialization pulse on the global reset input upon start-up.

  1. Incremental DSM Mode (Input 2 Low):

    • Use the ADC’s oversampling frequency as the input clock for the filter.
    • Set the main reset signal to match the desired decimation rate.
    • For example, with a 50 MHz ADC frequency, setting the reset signal to 25 MHz achieves a decimation factor of 2.
  2. Regular DSM Mode (Input 2 High):

    • The default decimation factor is set to 16.
    • For customized decimation factors, follow the configuration steps in Incremental DSM mode.

Testing Procedure

  1. Hardware Setup:
    • Connect a 1-bit ADC output to Input 1.
    • Set Input 2 to low for Incremental DSM or high for Regular DSM.
  2. Verification:
    • Incremental DSM: Set Input 2 low, connect a clock to the reset input, and observe decimated output changes.
    • Regular DSM: Set Input 2 high, then observe the decimated output, which updates at a rate of 16 samples.

Output Configuration

The decimation filter’s 16-bit output is divided as follows:

  • Most Significant 8 Bits (MSBs): Directed to dedicated output pins.
  • Least Significant 8 Bits (LSBs): Directed to general-purpose IO pins.

Compatibility

This filter is compatible with 1-bit output ADCs, either Incremental or Regular Delta-Sigma Modulator (DSM) types.

IO

#InputOutputBidirectional
0Xdecimation_output[8]decimation_output[0]
1type_decdecimation_output[9]decimation_output[1]
2global_resetdecimation_output[10]decimation_output[2]
3decimation_output[11]decimation_output[3]
4decimation_output[12]decimation_output[4]
5decimation_output[13]decimation_output[5]
6decimation_output[14]decimation_output[6]
7decimation_output[15]decimation_output[7]

Chip location

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