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

1 System Description

Single or multi-turn absolute rotary angle encoders support numerous applications including servo drives, industrial robots, and collaborative humanoid robots where precision mechanical angle positioning is required. The predominant types of position sensors are optical, magnetic, and inductive or capacitive. Large currents in nearby wiring necessitate advanced sensor technologies. One example is inductive sensors, which operate effectively in magnetic environments. Inductive sensors are immune to external stray fields and provide reliable measurements.

Figure 1-1 shows how this reference design demonstrates an absolute single-turn inductive rotary angle encoder. This inductive encoder is composed of three printed circuit boards (PCBs), the rotating target PCB, which is connected to the rotating motor shaft, and the stationary coil and signal chain PCBs.

TIDA-010961 Inductive Angle Sensing PrincipleFigure 1-1 Inductive Angle Sensing Principle

The coil PCB contains two sets of exciter coils and receiver coils. The two sets of receiver coils implement 16 and 15 periods per turn to detect the absolute position at start-up, and offer a higher resolution compared to less periods per turn. The coil PCB connects to the signal chain PCB, which employs the dual LDC5072 inductive front ends and the MSPM0G3507 microcontroller. Figure 1-2 shows the rotating target PCB is a passive disc with conductive dual pattern printed on the PCB and a 58mm diameter.

TIDA-010961 Target and Sense Coil PCBFigure 1-2 Target and Sense Coil PCB

Two LDC5072 inductive front-end ICs each produce high-frequency excitation signals. These signals are injected directly into corresponding exciter coils. The excitation coils generate a secondary voltage on the receiver coils depending on the rotary angle position of the target relative to the receiver coils. A signal representation of the position is obtained by reading in the voltages from the receiver coils. Each of the two LDC5072 devices process the signal, filter out the high-frequency excitation frequency, and provide an amplitude-modulated differential analog sine and cosine signal which tracks the electrical angle. The internal ADC of the MSM0G3507 samples LDC5072 output signals at a 32kHz rate. The sensor performs initial gain and offset calibration on two signal tracks: one with 16 periods and the other with 15 periods. The sensor then detects rotary position start-up and calculates high-resolution absolute angles continuously.