TIDUFG0 November   2025

 

  1.   1
  2.   Description
  3.   Resources
  4.   Features
  5.   Applications
  6.   6
  7. 1System Description
  8. 2System Overview
    1. 2.1 Block Diagram
      1. 2.1.1 PCB Rogowski Coils
      2. 2.1.2 Integrator Stage
      3. 2.1.3 Input Stage
      4. 2.1.4 Differential Amplifier Stage
      5. 2.1.5 High-Bandwidth, Low-Noise Amplifier Stage
        1. 2.1.5.1 Hybrid Integrator
        2. 2.1.5.2 Band Pass Filter
        3. 2.1.5.3 Logarithmic Amplifier
    2. 2.2 Design Considerations
      1. 2.2.1 Component Selection
      2. 2.2.2 RC Component Selection
      3. 2.2.3 Gain Setting
    3. 2.3 Highlighted Products
      1. 2.3.1 INA333
      2. 2.3.2 TLV9002
      3. 2.3.3 LM2664
      4. 2.3.4 TLV2387
      5. 2.3.5 LOG300
      6. 2.3.6 TL081H
  9. 3Hardware, Software, Testing Requirements, and Test Results
    1. 3.1 Hardware Requirements
    2. 3.2 Test Setup
      1. 3.2.1 Metering Setup
        1. 3.2.1.1 Accurate Current Source
        2. 3.2.1.2 TIDA-010987
        3. 3.2.1.3 ADS131M08 Metrology Evaluation Module
        4. 3.2.1.4 GUI
      2. 3.2.2 5kHz to 50kHz Band Pass and Logarithmic Amplifier Test Setup
        1. 3.2.2.1 Oscilloscope
        2. 3.2.2.2 Function Generator
    3. 3.3 Test Results
      1. 3.3.1 No Load Conditions
        1. 3.3.1.1 Objective
        2. 3.3.1.2 Setup
        3. 3.3.1.3 Requirements
        4. 3.3.1.4 Results
      2. 3.3.2 Starting Load Test
        1. 3.3.2.1 Objective
        2. 3.3.2.2 Setup
        3. 3.3.2.3 Requirements
        4. 3.3.2.4 Results
      3. 3.3.3 Active Power Measurements
        1. 3.3.3.1 Objective
        2. 3.3.3.2 Setup
        3. 3.3.3.3 Requirements
        4. 3.3.3.4 Results
      4. 3.3.4 Variation of Power factor
        1. 3.3.4.1 Objective
        2. 3.3.4.2 Setup
        3. 3.3.4.3 Requirements
        4. 3.3.4.4 Results
      5. 3.3.5 Variation of Voltage Test
        1. 3.3.5.1 Objective
        2. 3.3.5.2 Setup
        3. 3.3.5.3 Requirements
        4. 3.3.5.4 Results
      6. 3.3.6 Variation of Frequency
        1. 3.3.6.1 Objective
        2. 3.3.6.2 Setup
        3. 3.3.6.3 Requirements
        4. 3.3.6.4 Results
      7. 3.3.7 Band Pass
        1. 3.3.7.1 Objective
        2. 3.3.7.2 Setup
        3. 3.3.7.3 Requirements
        4. 3.3.7.4 Results
      8. 3.3.8 Logarithmic Amplifier
        1. 3.3.8.1 Objective
        2. 3.3.8.2 Setup
        3. 3.3.8.3 Requirements
        4. 3.3.8.4 Results
  10. 4Design and Documentation Support
    1. 4.1 Design Files
      1. 4.1.1 Schematics
      2. 4.1.2 BOM
      3. 4.1.3 PCB Layout Recommendations
        1. 4.1.3.1 Layout Prints
    2. 4.2 Tools
    3. 4.3 Documentation Support
    4. 4.4 Support Resources
    5. 4.5 Trademarks
  11. 5About the Author

2.1.2 Integrator Stage

The voltage (VS) induced at the output of a Rogowski coil is proportional to the time rate of change of current flowing in the primary conductor (IP). The output voltage has a 90° phase shift and lags input for a sinusoidal input current. Because the output of the Rogowski coil is proportional to the derivative of the instantaneous primary current, an integrator is required to retrieve the original current signal. The output voltage is linear, which can be used without integration in applications requiring only current measurement. For applications requiring measurement of power, the phase difference between current and voltage is important and requires phase shifting of the Rogowski current sensor output. Phase shifting is accomplished using an integrator. A Rogowski integrator can be implemented in two ways:

  • Digital (software) integration: Integration in the frequency domain results in –20dB/decade attenuation and a constant 90-degree phase shift. Phase angle correction accuracy improves significantly when accomplished digitally, due to precise phase and magnitude response control. Accurate digital integration requires high-performance microcontrollers (MCUs) and analog-to-digital converters (ADC) with digital filter implementation. Delayed processing occurs during start-up, attributed to the complexity of digital filter implementation. Digital filters are executed by MCUs and ADCs in the system.
  • Hardware integration: A hardware integrator can also be used for correcting the Rogowski current sensor phase shift. Phase correction can be achieved using a passive integrator (resistors, capacitors) or an active integrator (combination of active (op amp) and passive elements). The reference design implements a stable op amp-based active integrator that can be used over the useful temperature range. A well-designed hardware integrator introduces a 90° phase shift; however, practical limitations can result in phase errors and inaccuracies. Carefully choosing components minimizes the phase error variations.

Rogowski coil output, especially PCB Rogowski coil output, is very low (10μV/A–100μV/A). The low output becomes an issue at lower currents, for example 100mA, where the signal needs to be amplified by (100V/V–500V/V) depending on the coil sensitivity. The active integrator circuitry acts as an attenuator while shifting the current waveforms by 90 degrees. Attenuating the low input signal decreases the accuracy because the signal becomes very low where the signal hits the noise floor of the ADC. The gain of the integrator must be set to unity gain to cancel the integration attenuation at the frequency of interest (50Hz–60Hz). To achieve 90 degrees phase shift and gain of one, passive components must be calculated correctly and the component type must be the right type for math operation. For a discrete approach, thin film resistors and C0G and NP0 capacitors are recommended for high precision applications.