1. PSPICE 计算机仿真 Simulation Program with Integrated Circuit Emphasis

2. CH5 OPERATIONAL AMPLIFIER 运算放大器

3. 5.1 Modeling OP Amps with Resistors and Dependent Sources How to use PSpice to analyze a circuit containing an operational amplifier?

4. Fig.53

5. Example7 The parameters for the operational amplifier in the circuit shown in Fig.53 are Ri=200kΩ, A=10E4, and Ro=5kΩ. 1)Use PSpice to find Vi and Vo when Vg=1V(dc). 2)Compare the PSpice solution with the analytic solution for Vi and Vo.

6. 预备知识 An equivalent circuit for an operational amplifier (Fig. 52)

7. Fig. 52 ex7_pre_ddb

8. Solution Analog lib: R, E(VCVS) Source lib: VDC

9. Fig. 54 ex7_sch

10. Fig. 55 output file

11. 1)We used simple bias point analysis, therefore, V(in) = -0.0028V( 书上 :0.0027V--?) V(out) = -10.03V( 书上 :-9.9697V--?)

12. Ideal operational amplifer If we assume that the operational amplifer in the circuit shown in Fig. 53 is ideal, we can altera the PSpice op amp schematic representation by making Ri and A very large and Ro=0.

13. To illustrate, we modify the schematic in Fig. 54, with R2=200 MΩ, A=10E8, and R4 removed from the schematic entirely. (Fig. 54a)

14. Fig. 54a

15. The resulting PSpice output file after bias point analysis is shown in Fig. 56. The values of vi and vo from this simulation are Vi=v(in)=-10E-9V ( 书上 :100E-9V--?) Vo=v(out)=-10V

16. Fig. 56 output file

17. 2)We obtain the analytic solution for Vi and Vo by solving the following simultaneous node-voltage equations:

18. You should verify that the solutions for Vi and Vo are Vi=2.742mV Vo=-9.970V

19. 5.2 Using OP Amps Library Models

20. Example8 Repeat the analysis of the circuit shown in Fig.53, but this time use the uA741 model from the PSpice model library.

21. Solution uA741 在 EVAL 库中 ; 需要在 Place Part 对话框，点 Add Library … 按钮，添加该元件库。

22. Fig. 57a Add EVAL Library

23. Fig. 57b EVAL Path

24. Fig. 57 ex8_sch

25. Fig. 58 output file

26. 5.3 Modifying OP Amp Models Place the model of the uA741 from the Eval Library in your circuit schematic. Highlight the op amp component, select Edit/PSpice Model from the Capture menu. (Fig. 59a)

27. Fig. 59a

28. Fig. 59 Model Editor

29. You define a subcircuit by inserting a.SUBCKT control statement.SUBCKT SUBNAME N1 N2 N3 You terminate the subcircuit description by inserting an.ENDS control statement.ENDS

30. Now we create a new subcircuit based on the ideal op amp, consisting of a 1MΩ input resistor, a voltage-controlled voltage source with a gain of 10E6, and a 200 Ω output resistor.

31. Fig. 60 Model Editor for IdealOpAmp

32. Highlight the IdealOpAmp component; Select Edit/Part from the Capture menu; The result should look like the part shown in Fig. 61.

33. Fig. 61 Edit model

34. Highlight the new IdealOpAmp component; Select Edit/Properties from the Capture menu. The modified template is shown in Fig. 62.

35. Fig. 62 Edit Property

36. example9 Repeat the analysis of the circuit shown in Fig.53, but this time use the IdealOpAmp model we have just created.

37. Solution

38. Fig. 63 ex9_sch

39. Fig. 64 output file

40. From Fig. 64, we can see that the output voltage is -10 V.