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

4.4.4 Impact of Air Gap on Noise, 4th Electrical Harmonics and Total Angle Accuracy

With the air gap increasing, the electromagnetic field generated by excitation coils reduces and leads to higher LDC5072 noise. This section analyzes the influence of the air gap on TIDA-010961. By using different motor shaft adapters, the air gap changes from 0.5mm to 1.2mm. Repeat the test procedure described in section. Figure 4-20 to Figure 4-25 show the test results.
TIDA-010961 Rotary Angle Accuracy Over One Mechanical Cycle at 0.5mm Air GapFigure 4-20 Rotary Angle Accuracy Over One Mechanical Cycle at 0.5mm Air Gap
TIDA-010961 Rotary Angle Accuracy Over One Mechanical Cycle at 0.8mm Air GapFigure 4-22 Rotary Angle Accuracy Over One Mechanical Cycle at 0.8mm Air Gap
TIDA-010961 Rotary Angle Accuracy Over One Mechanical Cycle at 1.2mm Air GapFigure 4-24 Rotary Angle Accuracy Over One Mechanical Cycle at 1.2mm Air Gap
TIDA-010961 Rotary Angle Accuracy Over One Electrical Cycle at 0.5mm Air GapFigure 4-21 Rotary Angle Accuracy Over One Electrical Cycle at 0.5mm Air Gap
TIDA-010961 Rotary Angle Accuracy Over One Electrical Cycle at 0.8mm Air GapFigure 4-23 Rotary Angle Accuracy Over One Electrical Cycle at 0.8mm Air Gap
TIDA-010961 Rotary Angle Accuracy Over One Electrical Cycle at 1.2mm Air GapFigure 4-25 Rotary Angle Accuracy Over One Electrical Cycle at 1.2mm Air Gap

Under different air gaps, the angle error are all below ±0.04 degrees. Besides, the rotary angle accuracy over one electrical cycle figure shows the harmonics vary with air gap changes.

FFT analysis is used to further analyze the air-gap influence on harmonics. TableTable 4-7 shows the results. At a lower air gap, the 4th harmonic is larger. But as air gap increases, the static noise goes higher and the 4th harmonic error decreases. There is a tradeoff between encoder resolution and encoder accuracy.

Table 4-7 Harmonic in Electrical Angle
AIR GAPSTATIC NOISE (DEG)(1)1ST HARMONIC (DEG)(2)2ND HARMONIC (DEG)(2)4TH HARMONIC (DEG)(2)
0.5mm0.00150.00680.00430.0110
0.8mm0.00230.00850.00420.0039
1.2mm0.00250.00800.00450.0038
(1) All data are 1-sigma RMS value
(2) The harmonic order is referred to electrical cycle