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

3.4 Temperature Stability

Temperature stability is required for the circuit, or the offset voltage drift over temperature is added as error to the output voltage. This phenomenon can appear even when the temperature in the room is changed by a few degrees; The graph indicates steep voltage change periodically that sync with the air conditioner is on. Not only IB drift but also input offset voltage (Vos) drift of the op amp appears as a dent of the output voltage. The circuit needs to be in the oven to maintain temperature during the measurement.

Vout Over Time in the Condition of Room Temperature Figure 3-14 Vout Over Time in the Condition of Room Temperature