1. ABE425 Engineering Measurement Systems Operational Amplifiers (OpAmps) Dr. Tony E. Grift Dept. of Agricultural & Biological Engineering University of Illinois

2. Agenda Packaging OpAmp as a near-ideal Voltage Amplifier Non-inverting OpAmp Virtual ground derivation Inverting OpAmp Virtual ground derivation Differentiating OpAmp Integrating OpAmp Voltage follower (buffer)

3. Dual-in-line (DIP) and Surface Mount Device (SMD) packaging

4. Typical OpAmp pin assignment (741)

5. OpAmp as a near-ideal Voltage amplifier Open loop amplification A very large Input impedance very high Output impedance very low OpAmp has a Voltage source output

6. Non-inverting OpAmp

7. Non-inverting OpAmp : Virtual ‘ground’ principle Since no current is flowing into the OpAmp: What is the input resistance for the source ?

8. Inverting OpAmp

9. Inverting OpAmp: Virtual ground principle Since no current is flowing into the OpAmp: What is the input resistance for the source ?

10. Capacitor equation Charge across Capacitor (Coulomb) Capacitance value (Farad) Voltage across Capacitor (Volt) Current through Capacitor (Ampere)

11. Integrating Inverting OpAmp : Virtual ground

12. Differentiating Inverting OpAmp: Virtual ground

13. Integrating Inverting OpAmp : Virtual ground

14. Differentiating Inverting OpAmp: Virtual ground

15. Unity gain OpAmp (Voltage follower, buffer) This circuit has no amplification, but provides a very high impedance input and low impedance output Use it after any sensor configuration to prevent loading errors You will need a symmetric power supply

16. Comparator function

17. OpAmp as comparator I What could this circuit be used for if Vref can be varied? Slope is termed ‘slew rate’

18. Voltage range detector When does the LED come on? Why do we need the diodes? How would you limit the current through the LED? When Vin > Vref_high OR Vin < Vref, low

19. Comparator with hysteresis (Schmitt Trigger)

20. Schmitt trigger as debouncer in noisy signals Regular comparatorSchmitt trigger with hysteresis

21. Subtracting OpAmp Use superposition!! Use virtual ground principle!! First consider

22. Subtracting OpAmp Use superposition!! Use virtual ground principle!! Next consider

23. Subtracting OpAmp Add influences of both sources

24. Current to voltage converter

25. Application current to voltage converter

26. Active filters combine amplification and filtering in one circuit! What is the input impedance the source ‘sees’?

27. Active Low-Pass filter analysis (1 st order) Without CIn general with impedances

28. Active High-Pass filter with OpAmp and Capacitor / Resistor pair (1 st order) What is the input impedance the source ‘sees’?

29. Active High-Pass filter analysis Without C In general with impedances

30. High-pass and low-pass section separated by OpAmp

31. ABE425 Engineering Measurement Systems Operational Amplifiers (OpAmps) The End Dept. of Agricultural & Biological Engineering University of Illinois