SBOA571 august   2023 OPA2387 , OPA387 , OPA4387

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Example Considerations
  6. 3Introducing a Preconditioning Circuit
    1. 3.1 First Order Shelving Filter
    2. 3.2 Second Order Shelving Filter
    3. 3.3 Noise Contribution of the Second Order Shelving Filter
    4. 3.4 DC and AC Gain
  7. 4Design Procedure for the Second Order Shelving Filter
    1. 4.1 Definition of Boundary Conditions
    2. 4.2 Calculation of Component Values
  8. 5Influence of Component Tolerances
  9. 6Summary
  10. 7References

Calculation of Component Values

Start values:

Equation 14. DCgain; ACgain; fp1; Q0.5; R1; C1 
  1. Select f p 1 (for example, 1/4th of lowest AC frequency); example 50 Hz AC to 12.5 Hz
  2. Select Q = 0.65 for maximum gain flatness
  3. Select C 1 based on component restrictions (large C)
  4. Calculate R 1 based on the desired f p 1 and component restrictions (small R)
  5. Trade of large C versus small R for best noise
    Equation 15. R 1 = 2 2 π   f P 1 × C 1
  6. Calculate R2:
    Equation 16. R2=2R1
  7. Calculate R3:
    Equation 17. R3=DCgain×R1
  8. Calculate R4:
    Equation 18. R4=ACgain×2R1
  9. Calculate C2:
    Equation 19. C2=C14Q2
  10. Calculate C3:
    Equation 20. C3=C1ACgain×2×DCgainDCgain+ACgain2
  11. Calculate C4:
    Equation 21. C4=C1ACgain×4Q2