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Joining discrete wave using op-amp - o/p wave voltage shift! HELP

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hotshot05

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I am working on a project in which I have to basically output the continuous waveform of the supplied discrete input wave. I am joining the discrete points linearly using an integrator circuit to join the points using a ramp. The following picture will make my project clearer.
**broken link removed**

The problem with this circuit is that the output wave is continuous but all the points of the discrete wave are not properly joined. Also the O/P wave continuously changes its voltage and moves upward. The following picture shows what I mean.
**broken link removed**
See the continuous wave continuously shifts upward.

I am not able to determine what is causing this voltage shift. Does anyone have an idea why this is happening?

P.S : I have tried LM324 and LM358 for making this circuit.
 

Your interpolator design ignores the behaviour of real integrators, that always have some drift. There a better ways to design a triangular interpolator, e.g. using a time discrete feedback from the integrator output to the difference amplifier instead of the delayed original signal.

Other possible ways are a lossy integrator, or a time-continuous interpolation filter instead of the integrator.
 

Also the O/P wave continuously changes its voltage and moves upward.
Click to expand...

Since your input signal is in the positive region, the capacitor on the middle op amp causes the output to soar toward the extreme positive, gradually.

- - - Updated - - -

It isn't clear whether your incoming signal consists of (a) a bargraph shape, or (b) consists of momentary volt readings with no signal in between.

If you want the output to resemble a bargraph, then you will need to supply samples more often, in order to maintain output at a given volt level until the next transition arrives.

It might help if you experiment with different values of the capacitor, so as to obtain a desired slope at the output.
 

In a detail view, there are two possible causes for integrator output drift
- scaling error between direct and delayed signal, respectively difference amplifier unbalance
- DC offsets

You can try to carefully adjust both terms independently. But as said, there will be always a residual drift.
That's why you should change to a different interpolator topology.
 

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