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Op Amp Models


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 ► BASIC OP AMP MODEL -  Level 1                                        

You've probably seen op amps in a variety of applications, but how do you simulate them? Here's a good place to start - the three basic stages of an op amp: 1) Differential Amplifier, 2) Gain / Frequency Response and 3 ) Output Buffer. Using basic SPICE devices, this model helps you simulate the frequency response and DC accuracy of your amplifier.

 

Basic op amp Model

 

 

 ► INTERMEDIATE MODEL - Level 2                                         

This SPICE model (Boyle style) is beginning to look like those created by many op amp manufacturers. Only slightly more complex than the basic model, it includes slew rate limiting. But, the main benefit is that many advanced behaviors - voltage and current limit, CMR behavior, additional poles and zeros - can be easily added to this model (see Level 3 model below.) You can download an Excel spreadsheet that calculates the component values given an op amp's specifications.

     

   Intermediate op amp Model

 

Simpler methods of creating gain, pole and slew rate behavior without transistors:

   Slew Rate Using LIMIT 

   Slew Rate Using TANH

 

 

  ► ADVANCED COMPONENTS - Level 3                                   

Learn to model advanced analog behaviors with the Level 3 Op Amp models. Each SPICE file below adds an advanced function - one at a time - to the Level 2 Op Amp Model. Take the functions you need, modify them if you like, or create your own op amp model.

Frequency Shaping Stages

2nd Gain Stage

Output Voltage Limiting 

Output Current Limiting 

Supply Rail Current

Common-Mode Rejection 

Input Voff and Ibias 

Add 2nd and 3rd Poles - Improved Response      new!

   

 

 

  ► EASY-TO-USE FUNCTIONS                                         

Here are some alternative - and typically easier - ways to implement various op amp functions.

Slew Rate Using LIMIT 

Slew Rate Using TANH

Output Voltage Limiter

Output Current Limiter 

 

OP AMP MODEL SUMMARY

  Model Level 1 Level 2 Level 3
  Differential Input

Open-Loop Gain

  1st Pole
(Frequency Response)
  Output Impedance
  Slew-Rate Limit  
  Internal Floating Nodes  
  Additional Frequency Shaping Stages    
  Correct Supply Rail Currents    
  Output Voltage and Current Limit    
  Input Offset Voltage    
  CMR Frequency Response    

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