Download - PSPICE 计算机仿真
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PSPICE 计算机仿真
Simulation Program with Integrated Circuit Emphasis
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CH5
OPERATIONAL AMPLIFIER运算放大器
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5.1 Modeling OP Amps with Resistors and Dependent Sources
How to use PSpice to analyze a circuit containing an operational amplifier?
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Fig.53
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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.
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预备知识 An equivalent circuit for an
operational amplifier (Fig. 52)
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Fig. 52 ex7_pre_ddb
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Solution Analog lib: R, E(VCVS) Source lib: VDC
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Fig. 54 ex7_sch
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Fig. 55 output file
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1)We used simple bias point analysis, therefore, V(in) = -0.0028V( 书上 :0.0027V--?) V(out) = -10.03V( 书上 :-9.9697V--?)
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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.
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To illustrate, we modify the schematic in Fig. 54, with R2=200 MΩ, A=10E8, and R4 removed from the schematic entirely. (Fig. 54a)
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Fig. 54a
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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
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Fig. 56 output file
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2)We obtain the analytic solution for Vi and Vo by solving the following simultaneous node-voltage equations:
0102001
1
oiii vvvv
045
10
10
4
oioio vvvvv
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You should verify that the solutions for Vi and Vo are Vi=2.742mV Vo=-9.970V
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5.2 Using OP Amps Library Models
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Example8 Repeat the analysis of the circuit
shown in Fig.53, but this time use the uA741 model from the PSpice model library.
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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。
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Fig. 57a Add EVAL Library
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Fig. 57b EVAL Path
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Fig. 57 ex8_sch
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Fig. 58 output file
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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)
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Fig. 59a
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Fig. 59 Model Editor
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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 <SUBNAME>
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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.
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Fig. 60 Model Editor for IdealOpAmp
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Highlight the IdealOpAmp component;
Select Edit/Part from the Capture menu;
The result should look like the part shown in Fig. 61.
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Fig. 61 Edit model
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Highlight the new IdealOpAmp component;
Select Edit/Properties from the Capture menu.
The modified template is shown in Fig. 62.
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Fig. 62 Edit Property
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example9 Repeat the analysis of the circuit
shown in Fig.53, but this time use the IdealOpAmp model we have just created.
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Solution
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Fig. 63 ex9_sch
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Fig. 64 output file
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From Fig. 64, we can see that the output voltage is -10 V.