Generate Real FFT IP

[Altera_Forum]

Hi, 

 I would like to generate a real 64 point FFT.  i.e. it takes 64 real input and generates 32 complex output bins.  As per myy initial analysis, Altera MEgacore generates only complex FFTs.  Q1) Does it supports real FFTs?   Q2) Is there any Altera IPs which performs the above mentioned funtions?  Thanks Nishanth

[Altera_Forum]

--- Quote Start ---  Hi,  I would like to generate a real 64 point FFT.  i.e. it takes 64 real input and generates 32 complex output bins.  As per myy initial analysis, Altera MEgacore generates only complex FFTs.  Q1) Does it supports real FFTs?   Q2) Is there any Altera IPs which performs the above mentioned funtions?  Thanks Nishanth  --- Quote End ---    just set imaginary input of altera ftt to zeros

[Altera_Forum]

--- Quote Start ---  just set imaginary input of altera ftt to zeros  --- Quote End ---    Thanks Kaz..  I understand setting imaginary to zero is an option.  But it need a 64 point complex FFT, which I feel is unnecessary.  Also I found a paper where it can do using 32 point FFT(in my example), by making odd and even values as real and imaginary.  But it needs some additional logic to be implemented on out put of FFT.  What I was interested is whether Altera provides such whole solution itself.?

[Altera_Forum]

--- Quote Start ---  Thanks Kaz..  I understand setting imaginary to zero is an option.  But it need a 64 point complex FFT, which I feel is unnecessary.  Also I found a paper where it can do using 32 point FFT(in my example), by making odd and even values as real and imaginary.  But it needs some additional logic to be implemented on out put of FFT.  What I was interested is whether Altera provides such whole solution itself.?  --- Quote End ---    Alera fft supports complex input/output f your input is real only then your imag is zero but fft output will be complex. You can't create imag input if you don' have it(it is zero if you don't have it).

[Altera_Forum]

Yeah sure.. but the multiplications will be complex even though the input is real...so its an easy but inefficient way of implementation 

 So i found this paper http://www.ti.com/lit/an/spra291/spra291.pdf  This paper explains how the symmetry of the twiddle factors can be exploited to implement 64point real FFT using 32 point complex FFT (by making odd numbered of input as real and even numbered input as complex)

[Altera_Forum]

It is possible to do two N-point FFT' s with a single 

N-point complex FFT:  http://www.engineeringproductivitytools.com/stuff/t0001/pt10.htm  If you have to do more than a single real FFT this might be of use.

[Altera_Forum]

--- Quote Start ---  It is possible to do two N-point FFT' s with a single N-point complex FFT:  http://www.engineeringproductivitytools.com/stuff/t0001/pt10.htm  If you have to do more than a single real FFT this might be of use.  --- Quote End ---    I was referring to the same approach.. I had posted 2 replies before but the administrator is yet to approve it :(