Opamp Models

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Op Amp Models

► 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 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

► 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

► EASY-TO-USE FUNCTIONS

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

Slew Rate Using TANH

Output Voltage Limiter

Output Current Limiter new!

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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