SLAA957 September   2020 MSP430AFE221 , MSP430AFE222 , MSP430AFE223 , MSP430AFE231 , MSP430AFE232 , MSP430AFE233 , MSP430AFE251 , MSP430AFE252 , MSP430AFE253 , MSP430F2003 , MSP430F2013 , MSP430F2013-EP , MSP430F423A , MSP430F4250 , MSP430F425A , MSP430F4260 , MSP430F4270 , MSP430F427A , MSP430F47126 , MSP430F47127 , MSP430F47163 , MSP430F47166 , MSP430F47167 , MSP430F47173 , MSP430F47176 , MSP430F47177 , MSP430F47183 , MSP430F47186 , MSP430F47187 , MSP430F47193 , MSP430F47196 , MSP430F47197 , MSP430F477 , MSP430F478 , MSP430F4783 , MSP430F4784 , MSP430F479 , MSP430F4793 , MSP430F4794 , MSP430F6720 , MSP430F6720A , MSP430F6721 , MSP430F6721A , MSP430F6723 , MSP430F6723A , MSP430F6724 , MSP430F6724A , MSP430F6725 , MSP430F6725A , MSP430F6726 , MSP430F6726A , MSP430F6730 , MSP430F6730A , MSP430F6731 , MSP430F6731A , MSP430F6733 , MSP430F6733A , MSP430F6734 , MSP430F6734A , MSP430F6735 , MSP430F6735A , MSP430F6736 , MSP430F6736A , MSP430F6745 , MSP430F67451 , MSP430F67451A , MSP430F6745A , MSP430F6746 , MSP430F67461 , MSP430F67461A , MSP430F6746A , MSP430F6747 , MSP430F67471 , MSP430F67471A , MSP430F6747A , MSP430F6748 , MSP430F67481 , MSP430F67481A , MSP430F6748A , MSP430F6749 , MSP430F67491 , MSP430F67491A , MSP430F6749A , MSP430F67621 , MSP430F67621A , MSP430F67641 , MSP430F67641A , MSP430F6765 , MSP430F67651 , MSP430F67651A , MSP430F6765A , MSP430F6766 , MSP430F67661 , MSP430F67661A , MSP430F6766A , MSP430F6767 , MSP430F67671 , MSP430F67671A , MSP430F6767A , MSP430F6768 , MSP430F67681 , MSP430F67681A , MSP430F6768A , MSP430F6769 , MSP430F67691 , MSP430F67691A , MSP430F6769A , MSP430F6775 , MSP430F67751 , MSP430F67751A , MSP430F6775A , MSP430F6776 , MSP430F67761 , MSP430F67761A , MSP430F6776A , MSP430F6777 , MSP430F67771 , MSP430F67771A , MSP430F6777A , MSP430F6778 , MSP430F67781 , MSP430F67781A , MSP430F6778A , MSP430F6779 , MSP430F67791 , MSP430F67791A , MSP430F6779A , MSP430FE423 , MSP430FE4232 , MSP430FE423A , MSP430FE4242 , MSP430FE425 , MSP430FE4252 , MSP430FE425A , MSP430FE427 , MSP430FE4272 , MSP430FE427A , MSP430FG4250 , MSP430FG4260 , MSP430FG4270 , MSP430FG477 , MSP430FG478 , MSP430FG479 , MSP430FG6425 , MSP430FG6426 , MSP430FG6625 , MSP430FG6626 , MSP430FR5041 , MSP430FR5043 , MSP430FR50431 , MSP430FR6005 , MSP430FR6007 , MSP430FR6041 , MSP430FR6043 , MSP430FR60431 , MSP430FR6045 , MSP430FR6047 , MSP430FR60471 , MSP430I2020 , MSP430I2021 , MSP430I2030 , MSP430I2031 , MSP430I2040 , MSP430I2041

 

  1.   Abstract
  2.   Trademarks
  3. 1Introduction: MSP Sigma-Delta ADCs and Common Applications
  4. 2MSP Sigma-Delta ADC Portfolio
  5. 3Sigma-Delta ADC Overview
  6. 4MSP Sigma-Delta ADC Features
    1. 4.1  ADC Inputs: Differential or Single-Ended
    2. 4.2  Input Channels: Independent or Multiplexed
    3. 4.3  Integrated Buffers
    4. 4.4  Integrated PGAs
    5. 4.5  Offset Calibration: Internal or External
    6. 4.6  Voltage Reference: Internal or External
    7. 4.7  ADC Modulator Clock Frequency: Fixed or Adjustable
    8. 4.8  Sampling Rate versus Data Rate
    9. 4.9  Conversion Mode: Single or Continuous
    10. 4.10 Groups of ADC Channels
    11. 4.11 Preload
    12. 4.12 Output Format: Unipolar or Bipolar Data
    13. 4.13 Module Synchronization
    14. 4.14 Architecture: Discrete-Time versus Continuous-Time
  7. 5Solutions to Common MSP Sigma-Delta ADC Configuration Issues
    1. 5.1 ADC Input Configuration
      1. 5.1.1 Settling Time Exceeds Recommended Minimum
      2. 5.1.2 Amplitude of the Input Signal Exceeds FSR
      3. 5.1.3 Missing Anti-Aliasing Filters
    2. 5.2 ADC Clocking Configuration
      1. 5.2.1 Incorrect Sampling Frequency
    3. 5.3 ADC Results
      1. 5.3.1 Unexpected Output Data Format
      2. 5.3.2 Low Resolution
      3. 5.3.3 Data Interpretation
    4. 5.4 Reference Module (REF) Configuration
      1. 5.4.1 Choosing Between an Internal or External Reference
      2. 5.4.2 Connecting the Recommended Capacitors
      3. 5.4.3 Delaying Conversions Until the Reference Settles
    5. 5.5 Hardware Recommendations
  8. 6Frequently Asked Questions
  9. 7References

5.1.3 Missing Anti-Aliasing Filters

The frequency content of the input signal can repeat itself around multiples of the ADC sampling rate - the duplicates are aliases of the original signal. If the anti-aliasing filters are missing, these aliases can increase noise in the digital output because their frequency exceeds the Nyquist rate. Remember that the sampling rate is actually the modulation frequency, so the recommended cut-off frequency of the anti-aliasing filters is typically 100 times less than the modulation frequency. Typically, the anti-aliasing filters are implemented using external first- or second-order resistor-capacitor (RC) filters that are connected to each differential input. Figure 5-2 shows how anti-aliasing filters are connected to the differential ADC inputs in a PIR motion detector design. To learn more, watch the Aliasing and Anti-Aliasing Filters training video.

GUID-20200922-CA0I-RVXK-LT64-VZJTJ4QCVVW8-low.gif Figure 5-2 Anti-Aliasing Filters Example