1. Chapter 31 Applications of Op-Amps

2. 2 Comparators Op-amp as a Comparator –No negative feedback –Output saturates with very small + or – input

3. 3 Comparators Comparator –Non-linear device –v out has two discrete values, ±V SAT –v out = +V SAT if + input is greater than – input –v out = –V SAT if – input is greater than + input

4. 4 Comparators A comparator circuit: Sine wave in, square wave out

5. 5 Comparators Input sine wave Output square wave V out = ±V SAT +V SAT (determined by V CC ) when sinusoid is + –V SAT (determined by V EE ) when sinusoid is – __ _ - __ _ - +-+- v out 741 V CC V EE

6. 6 Comparators Compare input waveform to reference Reference can be ground or dc source Can compare two waveforms Specialized comparator IC’s also available Detects when waveform reaches given level

7. 7 Comparators Zero-Crossing Detector

8. 8 Voltage Summing Amplifier Circuit

9. 9 Voltage Summing Amplifier Inverse sum

10. 10 Voltage Summing Amplifier Multiplies each input by

11. 11 Integrators and Differentiators In general Using resistors and capacitors –Integrators –Differentiators -+-+ __ _ - v out v in ZFZF Z1Z1

12. 12 Integrators and Differentiators Voltage across capacitor Current through capacitor

13. 13 Integrators and Differentiators Op-amp Integrator -+-+ __ _ - v out C R1R1 v in 0 V i i = 0

14. 14 + - Integrators and Differentiators Op-amp differentiator Circuit inherently unstable -+-+ __ _ - v out C in RFRF v in i i

15. 15 Integrators and Differentiators Stable op-amp differentiator

16. 16 Instrumentation Amplifiers Op-amp in differential amplifier configuration Noise suppression High CMRR Reasonable gain IC instrumentation amps

17. 17 Instrumentation Amplifiers An op-amp instrumentation amp circuit

18. 18 Instrumentation Amplifiers Measurement of very small voltages Transducer –Converts a physical change into an electrical change

19. 19 Instrumentation Amplifiers Strain gage –Converts force into ∆R –∆R is milliohms –Use bridge circuit

20. 20 Instrumentation Amplifiers Strain gage example –Thin metal foil (resistor) on plastic backing –Glued to metal bar –Bar subjected to tension and compression

21. 21 Instrumentation Amplifiers Strain gage example –Tension Resistance of strain gage is R + ∆R –Compression Resistance of strain gage is R – ∆R

22. 22 Active Filters Basic filter types –Passive elements, gain < 1 –Low-pass –High-pass –Bandpass –Band reject

23. 23 Active Filters With op-amps/active filters –Gain can be ≥ 1 –Filter response closer to ideal

24. 24 Active Filters Low-pass (R F = R 1 ) Add resistor for gain > 1 -+-+ __ _ - v out C R F = R 1 I = 0 0 V R1R1 v in

25. 25 Active Filters High-pass (R F = R 1 ) Add resistor for gain > 1 -+-+ __ _ - v out R F = R 1 I = 0 0 V R1R1 v in C

26. 26 Active Filters dc gain –Easily achieved –Not used much due to gain-bandwidth product Example –GBWP = 10 6, Gain = 10 –Cutoff for filter (HP or LP) only 10 5

27. 27 Active Filters Bandpass Wideband –Cascade HP and LP active filters –LP must have higher cutoff frequency –HP and LP cutoff frequencies far apart Narrowband –Can use single op-amp

28. 28 Active Filters Narrowband BP circuit -+-+ __ _ - v out 2R R1R1 C C __ _ - vinvin R

29. 29 Active Filters Active notch filter –Cascade narrowband BP filter –Adder circuit –Result is 1 – (frequency response of BP filter) –Frequency at resonant frequency of BP filter will be eliminated

30. 30 Voltage Regulation Voltage regulator –Constant voltage to load –Specified current range –Specified input voltage range –Zener diode regulator Inefficient Dissipates power

31. 31 Voltage Regulation Types of regulators –Fixed voltage regulator –Variable voltage regulator –Switching regulator Specialized IC regulators –For different voltages, e.g. +5 V, –5 V, +12 V, –12 V, +15 V, –15 V, etc.

32. 32 Voltage Regulation Line Regulation –Small output change with change in input RLRL __ _ - Regulated output Voltage regulator Unregulated input

33. 33 Voltage Regulation Load regulation –Small output voltage change with smaller R L –V NL = no-load voltage (open-circuit load) –V FL = full-load voltage (specified by manufacturer)

34. 34 Voltage Regulation Circuit to increase efficiency of Zener regulator with an op-amp +-+- Q1Q1 Unregulated input RDRD R1R1 R2R2 v out + - __ _ - v in + -

35. 35 Voltage Regulation Three-terminal IC regulators –7800 series, positive voltage –7900 series, negative voltage

36. 36 Voltage Regulation 5 V output, 7805 12 V output, 7812 –5 V output, 7905 –12 V output, 7912 RLRL __ _ - V out =12 V μA7812 Unregulated input + - + - __ _ - INOUT COM

37. 37 Voltage Regulation Ripple Greatly reduced by IC regulator V r(in) = input ripple voltage V r(out) = output ripple voltage