Page 105 - DSP Integrated Circuits

90 Chapter 3 Digital Signal Processing

procedure Unscramble;
var
temp : Complex;
k, q : integer;
begin
for k := 0 to N - 1 do
begin
q := Digit_Reverse(k);
if q > k then
begin
temp := x[k];
x[k] := x[q];
x[q] := temp;
end;
end;
end;

Box 3.5. Unscrambling

The algorithm consists of M = log2(AO stages and a final reordering of the out-
put sequence. The last stage, which is called unscrambling, is not needed in all
applications [22, 35]. Each stage consists of N/2 basic signal-flow graphs of the
type shown in Fig. 3.24.

Figure 3.23 Signal-flow graph for the Cooley-Tukey's FFT