How could i explain this wave form?
Is actually a straight line when use big y-axis scale,
but why if small scale ike this??

 

How could i explain this wave form?
Is actually a straight line when use big y-axis scale,
but why if small scale ike this??

Why do you think it is strange?

 

The lousy old LM324 is one of the oldest and noisiest (hissss) opamps ever made. I think you see its noise on the graph.

The 10k resistor feeding the 15nF capacitor is a lowpass filter which is supposed to reduce the response at 1066Hz to -3dB and cut higher frequencies more but your graph doesn't show it.

Maybe your signal is turned off and you are looking at the amplitude of the opamp's noise for the different frequencies. The LM324 has a very poor high frequency response.

 

The line on your graph is effectively smooth. The zoom is just so high.

 

I agree with Veritas. Jaywin you have to understand that in electronics you cant have the perfect values you would like. The thing you have to have in mind is that for every circuit you design you need to design that circuit with an accuracy sufficient to make the job. But you cant take the perfect values you imagine.

 

ya, the wave is not strange but just want to know how to
explain the small noise there.
Thanks everyone...

 

If you use a modern low noise opamp like an OPA134 single, OPA2134 dual or OPA4134 quad then you probably won't see the noise on your graph. Their bandwidth is a lot wider also.