How can I use opamp or any component for my problem ?

[Hero999]

Oh yes you do need a rectifier.

It also dosn't need a rectifier, just a simple RC filter on the comparator output

If does need a rectifier as the signal consists of both positive and negitive components, stick an RC filter on the end and you'll loose everything as the positive and negitive sides will cancel.

You need a rectifier to get rid of the negitive side first before you can use a low pass filter. This is exactly the same as tuning into an AM radio station, to get the audio superimposed on the RF signal it needs to be rectified before you do anything else.

I suggested an amplifier because at such low voltages the input ofset error and linear region of a comparator might start to become issues, an amplifier will help make it more stable, although it isn't essential.

 

[ericgibbs]

If does need a rectifier as the signal consists of both positive and negitive components, stick an RC filter on the end and you'll loose everything as the positive and negitive sides will cancel.

You need a rectifier to get rid of the negitive side first before you can use a low pass filter. This is exactly the same as tuning into an AM radio station, to get the audio superimposed on the RF signal it needs to be rectified before you do anything else.

I suggested an amplifier because at such low voltages the input ofset error and linear region of a comparator might start to become issues, an amplifier will help make it more stable, although it isn't essential.

hi hero,
The comparator will remove the 'negative component', as its a threshold detector.
Set it for say, +80mV and everything below that value will NOT be output, input signals over +80mV will be above the threshold and will change the state of the comparator output.

The 'spike' component at the output of the compartor will be integrated out by the RC filter.

I dont see any reason to explain it in AM radio terms.

I must point out I have used compartors many times in my products and I have lots of experience in their use.

I still would like an answer from the OP regarding the period times I have asked about.

EDIT: hero,
For reference, I have tested a LM393 comparator using a signal of the same amplitude/polarity and 'noise' as the OP's drawing.
As I still dont know the freq/period of the OP's waveform I have assumed something about 100KHz.
The switching level Vref set at +80mV, with a 10M/10K positive feedback gave a switching threshold of +72/78mVolt[6mV diff]
with a well defined output signal of about +0.2/+4.8v, with a 3K3 pullup to +5V.

 

[audioguru]

An L272 is a horrible dual power opamp. It has input offset voltage and input bias currents that are much higher than any other normal dual opamp.

Even a lousy old LM358 dual opamp is much better.

 

[karekok]

hi,

Tell me what the 'p1' , 'p2' time periods are, also the frequency of the spikes, refer the gif drawing.

Then I will try to help.

hi;

monday i can send informations. ı will be back you in monday. thanks

 

[karekok]

An L272 is a horrible dual power opamp. It has input offset voltage and input bias currents that are much higher than any other normal dual opamp.

Even a lousy old LM358 dual opamp is much better.

i will try to find LM358

 

[Hero999]

hi hero,
The comparator will remove the 'negative component', as its a threshold detector.
Set it for say, +80mV and everything below that value will NOT be output, input signals over +80mV will be above the threshold and will change the state of the comparator output.

I see that but it'd still switch at the harmonic frequency, so instead of having one pulse on the output per input pulse in you'll get lots of pulses and whether the comparator can keep up is another matter altogether

Are you talking about putting the RC filter on the output of the comparator?

That would certainly make sense but wouldn't another comparator after it be a good idea to square it up?

 

[karekok]

hi,

Tell me what the 'p1' , 'p2' time periods are, also the frequency of the spikes, refer the gif drawing.

Then I will try to help.

i just added timings.

 

[ericgibbs]

i just added timings.

hi,
I'll post a drawing today, did you get the LM393 comparator?

 

[ericgibbs]

hi,

This attached circuit works using a LM393 comparator.

If the signal output from the 1st half of the LM393 isn't 'square' enough after the R1/C1 filter, use the 2nd half of the LM393 to square it up.

Lets know how it goes.

EDIT: Added 2nd LM393 stage.

 

[karekok]

hi,
I'll post a drawing today, did you get the LM393 comparator?

i have lm358. is it problem ?

 

[ericgibbs]

i have lm358. is it problem ?

Hi,
YES it is!

 

[karekok]

hi,

This attached circuit works using a LM393 comparator.

If the signal output from the 1st half of the LM393 isn't 'square' enough after the R1/C1 filter, use the 2nd half of the LM393 to square it up.

Lets know how it goes.

EDIT: Added 2nd LM393 stage.

i m just building it.

 

[ericgibbs]

i m just building it.

hi,
Let us know how it goes, the one on the bench works OK. [LM393]

 

[karekok]

hi,
Let us know how it goes, the one on the bench works OK. [LM393]

no answer.... but still trying.