1. ELECTRIC CIRCUITS ECSE-2010 Spring 2003 Class 9

2. ASSIGNMENTS DUE Today (Monday): Tuesday/Wednesday: Thursday:
Homework #3 Due
Activity 9-1, Op-Amp ILM (In Class)
Tuesday/Wednesday:
Will do Experiment #4 in Class (EP-4)
Activity 10-2 (There is no 10-1)
Thursday:
Experiment #2 Report is Due
Will do Computer Project #1 in Class (CP-1)
Will spend second hour reviewing for Exam I
Exam I Monday, 2/10, 7-9, DCC 308

3. THEVENIN EQUIVALENT CIRCUIT
Define v, i using Active Convention

4. ACTIVITY 8-1

5. ACTIVITY 8-1

6. REVIEW Real Voltage Sources:
Model with Ideal Voltage Source, Vs, in Series with Resistor, Rs
Vs = Open Circuit Voltage
Rs = Source Resistance
Vs in Series with Rs can be viewed as the Model for a Real Voltage Source or as the Thevenin Equivalent Circuit for any Source Network

7. REAL SOURCES

8. REVIEW Power Transfer: For PMAX to RL:
Model Any Source or Source Network with Vs in Series with Rs
Model Any Load Network with Req
Rs is Usually Fixed
Want to Get Maximum Power to Load, RL
For PMAX to RL:
Choose Req = Rs
Best you can do

9. MAXIMUM POWER TRANSFER

10. END OF MATERIAL FOR EXAM I

11. VOLTAGE AMPLIFIER

12. AMPLIFIER CIRCUIT MODEL

13. AMPLIFIERS
An Amplifier is a Circuit that Multiplies a Voltage or Current by some Constant:
Vout = A x Vin
A is called the “Gain” of the Amplifier
Circuit Model for Voltage Amplifier:
Rin is called the Input Resistance
Could be Req of a complicated circuit
Rout is called the Output Resistance
Amplification Modeled with VCVS; A Vin
Gain = Vout / Vin = A

14. AMPLIFIER CIRCUIT

15. AMPLIFIERS Use Voltage Divider Rule at Input:
vin = [Rin / (Rin + Rs)] vs
Use Voltage Divider Rule at Output:
vout = [Req / (Req + Rout)] A vin
Overall Voltage Gain for Complete Circuit is vout / vs:
Gain = [Req / (Req + Rout)] A [Rin / (Rin + Rs)]
Choose Rout << Req; Rin >> Rs ; Design Challenge
Gain = vout / vs ~ A

16. AMPLIFIER CIRCUIT

17. OPERATIONAL AMPLIFIERS
Special Type of Amplifier:
Rin ~ 10 M; (Very Large)
Rout ~ 100 ohms; (Very Small)
Gain = A ~ 105; (Very Large)
Building Blocks for Electronic Circuits
Will Use Special Symbol for Op Amp:
Triangle: 2 Inputs, vp, vn; 1 Output, vout
vout = A (vp - vn); Difference Amplifier
See Circuit Model for Real Op Amp
Requires DC Sources; +VDC, -VDC
vout Can Never Be Greater than VDC

18. OPERATIONAL AMPLIFIERS

19. REAL OP AMP MODEL

20. Fig The 741 op-amp circuit. Q11, Q12, and R5 generate a reference bias current, IREF, Q10, Q9, and Q8 bias the input stage, which is composed of Q1 to Q7. The second gain stage is composed f Q16 and Q17 with Q13 acting as active load. The class AB output stage is formed by Q14 and Q20 with biasing devices Q18 and Q19 and an input buffer Q23. Transistors Q15, Q21, Q24, and Q22 serve to protect the amplifier against output short circuit and are normally off.

21. IDEAL OP AMP Ideal Op Amp is Op Amp with:
Rin ~ Infinite
Rout ~ 0
A ~ Infinite
Ideal Op Amp is a Good Circuit Model for Almost All Real Op Amps:
We will assume all Real Op Amps can be modeled by Ideal Op Amps
Will see in Computer Project 1 that the difference between a circuit with a Real Op Amp and an Ideal Op Amp is very small

22. IDEAL OP AMP

23. IDEAL OP AMP For Ideal Op Amp: Ideal Op Amp => Comparator Circuit:
ip = in = 0; Ideal Op Amp Draws NO Current!
This is because Rin is Infinite
BUT! vout Can Never Be Greater than VDC
Ideal Op Amp => Comparator Circuit:
If vp > vn => vout = +VDC
If vp < vn => vout = -VDC

24. OP AMP CIRCUITS
To Make Op Amp Circuits Useful We Must Add Negative Feedback:
Circuit connection between vout and vn
This will always keep vp = vn
Output, vout, will be Finite
Negative Feedback Creates “Virtual Short” at Input:
ip = in = 0; Always
vp - vn = vin = 0 With Negative Feedback

25. IDEAL OP AMP WITH NEGATIVE FEEDBACK

26. REAL OP AMP WITH NEGATIVE FEEDBACK

27. ISOLATION AMPLIFIER

28. ISOLATION AMPLIFIER Connect vout to vn: Connect vin to vp:
=> Negative Feedback
=> Virtual Short between + and – terminals
vp = vn; ip = in = 0
Connect vin to vp:
vout = vn = vp = vin; vout = vin
No Voltage Gain, BUT No Current is Drawn from Source!
“Isolates” Load from Source;
A very common application of an Op Amp

29. OP AMP CIRCUITS Assume Op Amp is Ideal
Use Virtual Short to find vout / vin
Virtual Short: ip = in = 0, vp = vn
Will Look at Effects of Real Op Amps Later
Computer Project 1 on Thursday
Will Use Circuit Model for Real Op Amp
Finite Rin, Non-Zero Rout, Finite A
Compare Performance of Circuit with that obtained by assuming an Ideal Op Amp

30. NON-INVERTING VOLTAGE AMPLIFIER

31. NON-INVERTING VOLTAGE AMPLIFIER
Use Resistors R1 and RF to Create Negative Feedback:
Ckt Path Between vout and vn => Negative Feedback
Creates Virtual Short
ip = in = 0

32. NON-INVERTING VOLTAGE AMPLIFIER
Connect vin to vp :
vn = vp = vin ; Virtual Short
i1 = vin / R1; Ohm’s Law
iF = i1; KCL
vout = vin + iF RF = vin (1 + RF/R1)
Non-Inverting Voltage Amplifier
Output Voltage is Same Sign as Input Voltage
Gain > 1

33. INVERTING VOLTAGE AMPLIFIER

34. INVERTING VOLTAGE AMPLIFIER
Use Resistor RF to Create Negative Feedback:
Note Change in Terminals
Ckt Path Between vout and vn
Creates Virtual Short
ip = in = 0

35. INVERTING VOLTAGE AMPLIFIER
Connect vin to vn Through R1 and Connect vp to Ground:
vp = 0 = vn
i1 = (vin - vn) / R1 = vin / R1; iF = i1
vout = 0 - iF RF = - (vin / R1) RF = - vin (RF / R1)
Output is Opposite Sign from Input
Inverting Voltage Amplifier
Gain > or < 1

36. SUMMING AMPLIFIER

37. ACTIVITY 9-1

38. ACTIVITY 9-1 Look for Known Amplifiers
Op Amp 1 is a Non-Inverting Voltage Amplifier
vx = ( / 2) vin = 20 vin
vp for Op Amp 2 is vx:
vn2 = vx
i = (vin - vx) / 3k = - 19 vin / 3k = iF2
vout = vx - iF2 60k
vout = 20 vin - (-19 vin / 3k) 60k = 400 vin
Gain = vout / vin = 400

39. ACTIVITY 9-1

40. OP AMP CAD MODULE

41. OP AMP CAD MODULE

42. OP AMP CAD MODULE

43. OP AMP CAD MODULE

44. TRANSISTOR BIAS POINT

45. TRANSISTOR BIAS POINT

46. EXPERIMENT #4

47. EXPERIMENT 4

48. OP AMP PACKAGE

49. 741 LAYOUT

50. EXPERIMENT #4