DSP Builder for Intel® FPGAs (Advanced Blockset): Handbook

ID 683337
Date 5/27/2022

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15.3.23. Twiddle Angle (TwiddleAngle)

The Twiddleangle block generates FFT twiddle factors when you use it between a counter and the TwiddleRom (or TwiddleRomF) blocks.

The TwiddleAngle block takes the output of the counter and splits it into three parts:

  • The channel field (LSBs of the counter)
  • The index field
  • The pivot field (MSBs of the counter)

It provides bitreverse(pivot) * index at the output. The calculation is optimized to use no multipliers and only a small amount of logic.

The TwiddleAngle block has an additional input: v, which keeps the internal state of the TwiddleAngle block synchronized with the counter. This input should be identical to the enable input to the counter.

Table 143.  Parameters for the TwiddleAngle Block
Parameter Description
K Width of the channel field.
Pivot width Width of the pivot field.
Index width Width of the index field.
Table 144.  Port Interface for the TwiddleAngle Block
Signal Direction Type Description
v Input Boolean Input to upcounter.
c Input Unsigned integer Output of upcounter.
angle Output Unsigned integer Input to TwiddleRom.