TIDUFF8 September   2025

 

  1.   1
  2.   Description
  3.   Resources
  4.   Features
  5.   Applications
  6.   6
  7. 1System Description
    1. 1.1 Key System Specifications
  8. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Considerations
    3. 2.3 Highlighted Products
      1. 2.3.1 LDC5072-Q1
      2. 2.3.2 MSPM0G3507
      3. 2.3.3 TPSM365R3
      4. 2.3.4 TLV9062
  9. 3System Design Theory
    1. 3.1 Hardware Design
      1. 3.1.1 Target PCB
      2. 3.1.2 Coil PCB
      3. 3.1.3 Signal Chain PCB
        1. 3.1.3.1 Inductive Angle Position Sensor Front-End Schematic
        2. 3.1.3.2 Differential to Single-Ended Signal Conversion
      4. 3.1.4 MSPM0G3507 Schematic Design
      5. 3.1.5 Power Supply Design
    2. 3.2 Absolute Position Calculation
    3. 3.3 Software Design
      1. 3.3.1 Angle Calculation Timing
      2. 3.3.2 Rotary Angle Error Sources and Compensation
  10. 4Hardware, Software, Testing Requirements, and Test Results
    1. 4.1 Hardware Requirements
      1. 4.1.1 PCB Overview
      2. 4.1.2 Encoder Interface
    2. 4.2 Software
    3. 4.3 Test Setup
    4. 4.4 Test Results
      1. 4.4.1 Inductive Sensor Sine and Cosine Noise Measurement
      2. 4.4.2 Absolute Angle Noise Measurement
      3. 4.4.3 Rotary Angle Accuracy Measurement
      4. 4.4.4 Impact of Air Gap on Noise, 4th Electrical Harmonics and Total Angle Accuracy
      5. 4.4.5 Power Consumption Measurement
  11. 5Design and Documentation Support
    1. 5.1 Design Files
      1. 5.1.1 Schematics
      2. 5.1.2 BOM
      3. 5.1.3 PCB Layout
      4. 5.1.4 Altium Project Files
      5. 5.1.5 Gerber Files
      6. 5.1.6 Assembly Drawings
    2. 5.2 Tools and Software
    3. 5.3 Documentation Support
    4. 5.4 Support Resources
    5.     Trademarks
  12. 6About the Author

4.4.1 Inductive Sensor Sine and Cosine Noise Measurement

Figure 4-4 and Figure 4-5 show the measured sine and cosine signals of the outer coil with 16 periods at the 7th sector over one electrical period. This corresponds to a mechanical angle from 135 degrees to 157.5 degrees. The maximum and minimum voltage of the sine is 3.036V and 0.123V. The cosine signal range is 3.176V and 0.232V. There is gain and an offset mismatch between the sine and cosine signals, which causes 1st harmonic electrical angle error. Minimize this error with calibration.

TIDA-010961 Sine Over One Electrical CycleFigure 4-4 Sine Over One Electrical Cycle
TIDA-010961 Cosine Over One Electrical CycleFigure 4-5 Cosine Over One Electrical Cycle

The following figures show the sine and cosine signal noise and histogram plots at a fixed 0.5 degrees mechanical angle. For the analysis, 2000 samples of the sine and cosine signals of the outer and inner loop where conducted at a sample rate of 32kHz with 8 × oversampling.

Table 4-4 shows the standard deviation, signal-to-noise ratio (SNR), and effective number of bits (ENOB) versus full-scale range. The absolute angle position data is calculated by the outer coil after the absolute angle is detected at start-up, the inner coil noise does not influence the final accuracy.

TIDA-010961 Outer Coil Sine Signal at 0.5 DegreesFigure 4-6 Outer Coil Sine Signal at 0.5 Degrees
TIDA-010961 Inner Coil Sine Signal at 0.5 DegreesFigure 4-8 Inner Coil Sine Signal at 0.5 Degrees
TIDA-010961 Histogram Outer Coil SineFigure 4-10 Histogram Outer Coil Sine
TIDA-010961 Histogram Inner Coil SineFigure 4-12 Histogram Inner Coil Sine
TIDA-010961 Outer Coil Cosine Signal at 0.5 DegreesFigure 4-7 Outer Coil Cosine Signal at 0.5 Degrees
TIDA-010961 Inner Coil Cosine Signal at 0.5 DegreesFigure 4-9 Inner Coil Cosine Signal at 0.5 Degrees
TIDA-010961 Histogram Outer Coil CosineFigure 4-11 Histogram Outer Coil Cosine
TIDA-010961 Histogram Inner Coil CosineFigure 4-13 Histogram Inner Coil Cosine
Table 4-4 Standard Deviation, SNR and ENOB versus MSPM0 ADC Full-Scale Range
PARAMETEROUTER COIL SINEOUTER COIL COSINEINNER COIL SINEINNER COIL COSINE
Sine/Cosine amplitude (V)1.45
Standard deviation (mV)0.732.002.132.24
SNR (dB)66.057.256.756.2
ENOB (bit)10.669.219.129.05