PSPICE?????

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PSPICE?????

• Simulation Program with Integrated Circuit
  Emphasis

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CH5

• OPERATIONAL AMPLIFIER
• ?????

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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 Ri200k?, A10E4,
  and Ro5k?.
• 1)Use PSpice to find Vi and Vo when Vg1V(dc).
• 2)Compare the PSpice solution with the analytic
  solution for Vi and Vo.

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????

• 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(??0.0027V--?)
• V(out) -10.03V(??-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 Ro0.

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• To illustrate, we modify the schematic in Fig.
  54, with R2200 M?, A10E8, 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
• Viv(in)-10E-9V (??100E-9V--?)
• Vov(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

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• You should verify that the solutions for Vi and
  Vo are
• Vi2.742mV
• 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?EVAL??
• ???Place Part???,?Add Library??,???????

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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 ltSUBNAMEgt

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