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

4.4.2 Absolute Angle Noise Measurement

For this test, the mechanical angle is fixed at 5.1 degrees. The angle is read at a 16kHz sample rate. For the analysis, 2000 samples are taken. Figure 4-14 and Figure 4-15 show the time domain noise and the histogram, respectively.

TIDA-010961 Static Angle at 5.1 Degrees Over 2000 Samples at 16kHz Sample RateFigure 4-14 Static Angle at 5.1 Degrees Over 2000 Samples at 16kHz Sample Rate
TIDA-010961 Histogram of the Angle at 5.1 DegreesFigure 4-15 Histogram of the Angle at 5.1 Degrees

Table 4-5 shows the corresponding standard deviation and ENOB versus full-scale position measurement range.

Table 4-5 Standard Deviation, SNR and ENOB at Static Mechanical Angle of 5.1 Degrees
PARAMETER ABSOLUTE ANGLE COMMENT
Standard deviation (degree)0.0015RMS
SNR (dB)101.6SNR = 20×log10 (±180 deg/STDEV)
ENOB (bit)16.6ENOB = (SNR – 1.76) / 6.02

For the following test the angle is changed at a 22.5 degrees interval to validate the noise floor over all 16 electrical periods, which equals one turn. There is no significant difference in each of the eight electrical periods. The peak-to-peak static angle noise is around 0.02 degrees and a maximum value occurs at 225 degrees.

TIDA-010961 Static Angle Noise Over One Revolution Figure 4-16 Static Angle Noise Over One Revolution

The following test is conducted to validate the static noise versus the air gap.

With the air gap increasing, the eddy current generated in the target board decreases and the output signal amplitude in the receiver coils also decreases, so the angle noise also becomes higher which means the encoder resolution is lower. When the air gap is increased to 1.5mm, the LDC5072 device on the inner coil runs into fault mode because the signal of the receiver coil is very small. Therefore, the absolute position cannot be calculated, keep the air gap smaller than 1.5mm.

Table 4-6 Angle Noise of Outer Coil versus Air Gap
Air Gap (mm)(1)0.5 (Default)0.81.21.5
Static Angle Noise (1 Sigma) (deg)0.00150.00230.00250.0048
(1) The air gap is the distance between top of target board and bottom of coil board.