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Visitor
2,292 Views
Registered: ‎07-17-2013

## block floating point

Hi, all. I have a question as to the block floating point in the FFT core.

The input data format is Q2.10, namely totally 12 bits wide, 2 bits integer, 10 bits fractional.

The IFFT length is 2048, output data width is still 12 bits, and configured using block floating point mode. After calculation, the block exponent is 7, which indicates the output has been shifted right by 7 bits.

How do I determine the location of the decimal point of the output data?

Thanks.

Visitor
2,281 Views
Registered: ‎07-17-2013

## Re: block floating point

To add some numerical example, say we have 2048 double precision data A, applying ifft to them, we get output of vector a.

Set A0 to be (-0.7071, -0.7071*j), the corresponding a0 = (0.0166, -0.0048*j).

By using Q2.10 format and 2's compliment, we get:

B0 = int(A0 * 2^10) = (3372, 3372*j).

The first output of IFFT core is b0 = (271, -80*j).

I found that:

b0 = a0 * 2^14;