Is There A Megafunction For Arctan ?

Don't know about pre built blocks.

By the way, if you have low number of input bit you can just store the function values in a Look Up Table.

How many input bits you have?

With 18bits a LUT is no feasible.

There are many options on the literature.

One is Cordic as previosuly reported.

Another option is a mix of ROM and linear (or quadratic interpolation).

Unfortunately it is not a simple task and a good approximation requires a careful analysis of the literature.

My group published many papers on these topics. As example:

1)

direct digital frequency synthesizers with polynomial hyperfolding technique (http://www.alteraforum.com/search/srchabstract.jsp?tp=&arnumber=1315881&querytext%3dde+caro%26refinements%3d4294967131%26openedrefinements%3d*%26searchfield%3dsearch+all)

De Caro, D.; Napoli, E.; Strollo, A.G.M.;

circuits and systems ii: express briefs, ieee transactions on (http://www.alteraforum.com/forum/../xpl/recentissue.jsp?punumber=8920)

Volume: 51 , issue: 7 (http://www.alteraforum.com/forum/../xpl/tocresult.jsp?isnumber=29164)

Digital Object Identifier: 10.1109/tcsii.2004.829553 (http://dx.doi.org/10.1109/tcsii.2004.829553)

Publication Year: 2004 , Page(s): 337 - 344

IEEE Journals

2)

high-performance special function unit for programmable 3-d graphics processors (http://www.alteraforum.com/search/srchabstract.jsp?tp=&arnumber=4694047&querytext%3dde+caro%26refinements%3d4294967131%26openedrefinements%3d*%26searchfield%3dsearch+all)

De Caro, D.; Petra, N.; Strollo, A.;

circuits and systems i: regular papers, ieee transactions on (http://www.alteraforum.com/forum/../xpl/recentissue.jsp?punumber=8919)

Volume: 56 , issue: 9 (http://www.alteraforum.com/forum/../xpl/tocresult.jsp?isnumber=5230335)

Digital Object Identifier: 10.1109/tcsi.2008.2010150 (http://dx.doi.org/10.1109/tcsi.2008.2010150)

Publication Year: 2009 , Page(s): 1968 - 1978

thanks a lot. but your links can not fonud. may be this can be a result of my browser.

so can I ask one more question?

have you any idea aboul kalman filter design with verilog ?

The links cannot work.

You've to search on IEEExplore website but you can download the papers only if your institution pays the IEEE.

With reference to Kalman...

sorry, it's not my expertise. I can't help.

Those links effectively do not work.

If you search for the titles on the web you will find them at IEEE, so you need access rights ($$$).

Cordic is a proven approach, well documented on the web (free) and in fact a simple algorithm.

Back in 2004 I made my own specific implementation in AHDL. I recompiled it today for 10 and 16 bits precision (16 bits is the maximum I projected at the time), if I extrapolate the LC usage an 18 bit cordic would use about 1150 LC (Cyclone I) and run at about 250 MHz in pipelined mode. Making it combinatorial will use about the same amount of LCs but will be a lot slower( est. 70 ns delay). I used a Cyclone EP1C4F324C6 device for the test compilations.

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You've to search on IEEExplore website but you can download the papers only if your institution pays the IEEE.

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I don't think that people that work for organizations that can afford the IEEE fees come to this forum (or any other) to seek help. (They will have access to adequate resources and experience in-house ...)

I propose to add a rule to the forum rules that all papers quoted must be freely accessible. Who will be putting $35,- (or so) down for an article you don't know whether it will help?

Universities pay the fee.

I come from an University and come to this forum to exchange ideas with people experts in the field.

I can assure you that in the Universities not everybody is an expert on Altera FPGA design. As a consequence web resources and forums are very much used to improve the quality of the work.

Further, I think that many University people, such as young master thesis students, come to this forums to seek advices for their projects.

These students usually have access to many on-line journals such as IEEE.

I don't want to start a polemic here (I sincerely hope I didn't).

A lot of people visiting this forum are not at a university or working in a large(r) company, yet are very experienced and have solved real-life projects. I think it is a matter of politeness that if you bring an argument into a discussion that other parties can explore that argument and eventually learn from it.