SLAA475A October   2010  – March 2019 MSP430L092

 

  1.   MSP430x09x Analog Pool: Feature Set and Advanced Use
    1.     Trademarks
    2. 1 MSP430x09x Overview
    3. 2 Analog Pool (A-Pool)
      1. 2.1  Input Dividers
      2. 2.2  Internal Reference
      3. 2.3  Starting and Stopping the A-Pool
      4. 2.4  Comparator Function
      5. 2.5  8-Bit DAC Function
      6. 2.6  8-Bit ADC Function
        1. 2.6.1 ADC Conversion Using Ramp
          1. 2.6.1.1 ADC Conversion Without Error Compensation
          2. 2.6.1.2 ADC Conversions With Overdrive Compensation
          3. 2.6.1.3 ADC Conversions With Offset Compensation
          4. 2.6.1.4 ADC Conversions With Overall Compensation
          5. 2.6.1.5 Windowed ADC Conversion
        2. 2.6.2 ADC Conversion Using SAR
        3. 2.6.3 Multiple ADC Conversions
        4. 2.6.4 Comparison Between Different Measurement Methods
        5. 2.6.5 Error Dependencies
      7. 2.7  SVM Function
      8. 2.8  Use of Multiple Features
      9. 2.9  Temperature Measurements With the A-Pool
      10. 2.10 Fractional and Integer Number Use
      11. 2.11 APINTB and APFRACTB Use With ATBU and EOCBU
      12. 2.12 A-Pool Trigger Sources
      13. 2.13 Filtering ADC Conversions With Digital Filters
    4. 3 Summary
    5. 4 References
  2.   Revision History

2.6.4 Comparison Between Different Measurement Methods

To compare the different methods regarding accuracy and speed, a few basic conditions must be taken into account. The parameters for the following comparisons are:

  • Because both program execution time and measurement time are relevant for the comparison, the program and ADC are supplied with the same clock speed.
  • The input value that is measured with the different methods is in the middle of the measurement range. This means the correct value is 0x80 in integer mode.
  • The internal reference is used. One count step equals 1 mV.
  • The Program Execution Clock Cycles column in Table 2 shows all clock cycles that are necessary to execute the measurement. No interrupt service routines or additional overhead, such as clock module settings, are included. The program execution cycle counter was determined by the cycle counter of the IDE.
  • The compared programs are not using filters.
  • All observations and measurement are done at room temperature.
  • The treated errors are only errors that can occur because of the design structure. In addition, the ADC values can be changed by noise.

Table 2 shows comparison of the conversion methods regarding execution speed and measurement accuracy.

Table 2. Comparison Between Different Measurement Methods

Measurement Method Maximum Error Program Execution Clock Cycles Measurement Only Clock Cycles ± Error Overall Clock Cycles Needed
Ramp without compensation ±3 44 (70) 128 ± 3 169 to 175
Ramp with offset compensation ±1 68 (150) 2 × (128 ± 1) 322 to 326
Ramp with overdrive compensation ±2 68 (142) 2 × (128 ± 2) 320 to 328
Ramp with overall compensation ±0 138 (288) (2 × (128 ± 2)) + (2 × (128 ± 1)) 692 to 704
Windowed ramp without compensation
(starting point 0x70)		 ±3 44 (71) 16 ± 3 57 to 63
Windowed ramp with overall compensation
(starting points 0x70 and 0x90)		 ±0 152 (288) (2 × (16 ± 2)) + (2 × (16 ± 1)) 210 to 222
SAR logic ±1 39 8 47