Digital Signal Processing - IP and Algorithms

[falconbombay]

In the xilinx fir compiler V4.0 ,The din is unsigned,coeff is two's complement,and then the dout is signed or unsigned ?

Please reply.

[vlavruhin]

Signed

[falconbombay]

Hi,

 It meanse that output of FIR filter is depend on the type of coefficients not on the input type whether ti is signed or unsigned.

I want to ask one more que. when we are selecting signed input type in IP  what should we give the input to FIR Complier i.e. straight binary or 2s complement?

And if I want to give the input (i.e. -1 to +1) to FIR IP how can I give?

thanks for quick reply.

[vlavruhin]

If it's signed, then it means two's complement.

In your case input's bitwidth is 8 bits.

So input values should be in range from -2^(8-1) = -128 = 10000000b (or it maps to -1.0 value) to 2^(8-1)-1 = 127 = 01111111b (that maps to 1.0 value).

[ywu]

I would suggest you google fixed point number representation. Vitaly showed an example of 8-bit fixed point numbers. In case it matters, 01111111b is not exactly 1.0 assuming 8.7 format. It's  0.992187500000000.

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falconbombay wrote:

Hi,

 It meanse that output of FIR filter is depend on the type of coefficients not on the input type whether ti is signed or unsigned.

I want to ask one more que. when we are selecting signed input type in IP  what should we give the input to FIR Complier i.e. straight binary or 2s complement?

And if I want to give the input (i.e. -1 to +1) to FIR IP how can I give?

thanks for quick reply.

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[vlavruhin]

Hi, Jim!

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In case it matters, 01111111b is not exactly 1.0 assuming 8.7 format. It's  0.992187500000000.

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Thank you for correction. Yes, if we have signed number with N bits and (N-1) fractional bits, then whole number range is from -2^(N-1) to [2^(N-1)]-1. And that's mapped to normalized half-closed interval [-1.0; 1.0), i.e. including -1.0 and excluding 1.0. It can be recalculated as closed interval [ -1.0; 1.0-2^(1-N) ].

[falconbombay]

Hi Vitaly and Jim,

Thank you for your replies.