I want to learn how to design butterworth IIR digital filter with low pass and designed by Z transform method
what specification I need to design
I know below
1) cutoff frequency
2)stop band frequency
3)Ripple in pass band
4)Filter order

what specification I need to know to design filter?

 

A little more information would be useful here. Are you looking for a software implementation, an algorithm of some sorts or a procedure for doing hand calculations?

In any case, there are plenty of resources available online for digital filters. A quick Google look-up resulted in this, this and this (for a Matlab implementation)

There is also this free ebook on DSP that you might find useful.

 

If it's a low-pass filter then you don't normally use the stop band frequency, only the cutoff (corner) frequency and filter order are needed.

 

I want to know procedure for doing hand calculations?

 

There is also this free ebook on DSP that you might find useful.

One of the two best technical books ever. He knows how to explain things.

 

@vead: There was some theory in the links I posted earlier. In any case, this looks pretty rigorous. Hope it helps.

One of the two best technical books ever. He knows how to explain things.

Indeed. I owe a significant part of my DSP know-how to this book. It was a huge help during my Signals course given how dry and math-intensive those tend to become. Just out of curiosity though, which is the other one?

 

. Just out of curiosity though, which is the other one?

Programming the Z80 by Ronald Zaks. Another monster who knows how to explain.