90 degrees phase shift

[jtamminen]

I have a sine-wave input, 45 to 60Hz, few hundred millivolts.

The sine wave might have some distorsions now and then, and these distorsions needs to be replicated at output. (kind of mains-current monitoring device).

The input varies from zero to some voltage, and is amplified to a 0-5volt level.

That is the easy part.. now the problem:

How could I "lag" the phase 90 degrees with analog design?

The frequency is as said, 45 to 60Hz, but a constant in one application. It is possible to use different components with different frequency..

I know it is easy to do with a micro, A/D and D/A along with a ring-buffer, but I need to avoid digital logic here...

Anyone able to give me a hint how this might be done?  The output should be as close to input wave-shape as possible.

Hope You understand my question, I'm not native english.

[slackjack]

How could I "lag" the phase 90 degrees with analog design?

Well a wave the lags a sine wave by 90 degrees is a -cosine wave. When we integrate a sine wave, we get a -cosine wave. To do this you could use an operational amplifer configured as an integrator. The output voltage is:


Notice that the integral has a negative (-) sign. Well the negative cosine and the negative integral will cancel out to give a postive output. To get the -cosine, feed the output to an invertor with a gain of 1.

I'm not sure how good this method is at replicating distortions though

[audioguru]

No. An integrator is also a lowpass filter and will reduce distortion.
Use an Allpass filter with its amount of phase-shift adjustable for the frequency.

[MP]

Here is how it is done for the audio range. Of course, this is for a sound effect. Add or take away phase shift stages as needed.

MP

[jtamminen]

Here is how it is done for the audio range. Of course, this is for a sound effect. Add or take away phase shift stages as needed.

MP

Thank You, I believe this will solve my problem!