That error was costly to me. Not in a monetary fashion thankfully.

Anyways, here's the page where I found the formulae that led me astray.

Here are the corrected design equations.

 

Thanks. That will remain a handy reference even though I had already adjusted my spreadsheet.

 

i need 2 nd order allpass filter desind using matlab. what is practical diagram for it? can any one help me?

 

For active filter designs, mostly lowpass, I use FilterLab from Microchip. It is good.

Not available in this PC, I cannot say if it contemplates "all pass" as well.

Download and give a try. Using it for long time.

 

Below is an interesting and simple All Pass circuit that uses a single RC network to give a phase-shift between 0° and 180° as the frequency changes. I think it may be equivalent to a standard 2nd order shift.

If you interchange the position of the R and C then you will reverse the direction of the phase shift.