Urgent... simulink doubt. Op amp model by transfer funstion-distorted output?

Before moving into a model of the real world op amp, I'm trying to model a basic op amp - first order - low pass filter transfer function, typical op amp open loop gain = 10^5 ; cut off frequency = 10^5 Hz, Therefore the tf is: 10^5 / (1 + s/(2*pi*10^5))

Unity negative feedback provided; (beta = 1) so that the closed loop transer function has a dc gain of approximately 1. Configuration parameters - variable step max step size - 1e-3(also tried 1e-4) min step - auto relative tolerance - 1e-3 absolute tolerance - auto refine factor - 1 simulation time - 0 - 0.005 sec (5 cycles for input is 1000 hz sine)

Doubt 1: The scope is giving only output for time - 0.0049 to 0.005 sec, also the ouput is distorted. ???

When i replaced the transfer function with "gain block(10^5) + analog filter block(butterworth low pass with pass band edge = 2*pi*10^5)":

Doubt 2: The scope is giving only output for time - 0.0049 to 0.005 sec, the ouput is not distorted. ???

A solution please...

[Walter Roberson]

http://www.mathworks.com/matlabcentral/answers/29922-why-your-question-is-not-urgent-or-an-emergency

Answer 1

[Walter Roberson]

By default, scopes only display the last 5000 points. You can alter their parameters to display everything.

Answer 2

[Avinash Bhat]

I understand and I'm sorry for posting it as an urgent post. And thank you for reminding me about the scope parameters.

Answer 3

[Erosoft]

Hi,

I've also some doubt using variable-step simulation with simulink.

In my model output copy input one of the 2 inputs A or B according to a 3rd input C with a variable scheduling.

The input signals have a length of 160 for a total time of 11s. When I retrieve the outpout signal its length is 11002 points for a total time of 11s. I can easily understand when I run a simulation with variable step matlab calculate more points to avoid missing changing state, but when I plot the 3 signals on the same figure, there's nothing good, the output signal doesn't match with one of the 2 signals A or B.

But I have notice that when I plot the 3 signals first 160 points on the same figure they match together. Furthermore when I compare the ouput signals [1:160] to the [161:11002] one it seems like if the second parts was an image of the first part expanded according to the time.

I seriously think that there's a bug to fix with Matlab, unless I have to correct a parameter option but I doubt I have seen nothing in the help.

I do not know, if my answer will help you to resolve your problem, but excuse me for translating my french to english.

David

[Kaustubha Govind]

David: It's hard to comment on your model without looking. I would recommend reporting this to MathWorks Tech Support with your model if you are confident that it is a bug.