SBOA597 November   2024 OPA928

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Architecture of Small Current Measurement
    1. 2.1 Coulombmeter
    2. 2.2 Using the Coulombmeter to Determine IB
    3. 2.3 Leakage of Integration Capacitor
  6. 3Benchmarking
    1. 3.1 Point to Point Wiring
    2. 3.2 Shielding
    3. 3.3 PCB Cleaning
    4. 3.4 Temperature Stability
  7. 4Calibration Using a Coulombmeter for Application Circuits
    1. 4.1 Calibration of Common Application Circuits
    2. 4.2 Calibration of Inverting Input
    3. 4.3 Calibration of Non-Inverting Input
    4. 4.4 Determine Resistance of the Capacitor Using Zero-Cross Method
    5. 4.5 Dielectric Absorption and Relaxation
    6. 4.6 Calibration at 85°C
    7. 4.7 Calibration at 25C
  8. 5Summary
  9. 6References

4.3 Calibration of Non-Inverting Input

Convert application circuits into the calibration mode

The second case is for the high-impedance node, which is the non-inverting input terminal of the op-amp, such as high-impedance sensor application.

Application Circuits for High-Impedance Non-Inverting Input Terminal Figure 4-5 Application Circuits for High-Impedance Non-Inverting Input Terminal

As shown in the drawing, disconnect the sensor and transform the circuit into a feedback loop with a buffer amplifier with gain. Short the inverting input to the ground.

Configuration for Non-Inverting Input Terminal Calibration Figure 4-6 Configuration for Non-Inverting Input Terminal Calibration

Insert an integration capacitor between the non-inverting input and Vcal. So that the circuit is in the calibration mode.

Non-Inverting Input Terminal Calibration Using a Coulombmeter Figure 4-7 Non-Inverting Input Terminal Calibration Using a Coulombmeter