How to deal with DC offset and replace it by AC-signal

[Poison_83]

Hello!

I need a little help with some analog design, my signal is a low frequency-signal about 0.2 - 5 Hz (~500mV pk-pk) with an DC offset for a couple of volts (2-4 V). This DC-level is not constant, it drops slowly over time.
Now I want to get rid of this DC-level and want my AC-signal lay between 0-1V (in this example).
To be clear, I want the min-value of the AC-signal to be my new baseline and want the signal to be positive.
How should I deal with this baseline problem, OP Amp feedback in some way?
Thanks...

/P83

 

[Meridian]

Re: DC Offset

Hello!

I need a little help with some analog design, my signal is a low frequency-signal about 0.2 - 5 Hz (~500mV pk-pk) with an DC offset for a couple of volts (2-4 V). This DC-level is not constant, it drops slowly over time.
Now I want to get rid of this DC-level and want my AC-signal lay between 0-1V (in this example).
To be clear, I want the min-value of the AC-signal to be my new baseline and want the signal to be positive.
How should I deal with this baseline problem, OP Amp feedback in some way?
Thanks...

/P83

You mean 'Offset-Null'?

Go to this link and check Figure 11...

 

[Poison_83]

Re: DC Offset

Hmm, didn't see your link! I'm totaly new here so maybe I don't know where to look or maybe I'm just blind?

But don't you use the "Offset-Null" to eliminate the internal offset-failure in the OP with a pot or something.
Maybe this way would work if the DC-level is stable, but in my example it is slowly sinking all the time.

 

[pravin_dwaramwar]

Re: DC Offset

dear just use a coupling capacitor or filter to remove dc offset from the signal

 

[teteamigo]

Re: DC Offset

AC-COUPLING + DC RESTORATION (clamped capacitor)

 

[lladnar23]

DC Offset

Since your AC component is very low in frequency (0.2Hz), it makes this task challenging. What you need is essentially a highpass filter with a corner frequency of something like 0.1Hz. This can be achieved with switched capacitor circuits, or with an active filter.

 

[masri]

hi

hi to solve the offset problem you have to use a cpacitor
if you want to just pass the positive portion of your signal you have to use half wave diode rectifier:idea:

 

[manju_bhat]

Re: DC Offset

i reckon if you use a coupling capacitor and filter (if it needed only) , the problem may solve.

 

[Poison_83]

DC Offset

Thank you for you answers.

When you say I can use only a capacitor, in what size should this be if I want my signal (~0.2-5Hz) not to be distorted in any way? Is this possible?

My idea was some kind of active filtering but I dont know what type of filter or values to get the cutoff frequency so low and without destroying the original signal.

 

[mydreamhouse]

Re: DC Offset

use a coupling capacitor