Visible to Intel only — GUID: hco1423077042230
Ixiasoft
Visible to Intel only — GUID: hco1423077042230
Ixiasoft
14.3.14. Hybrid FFT (Hybrid_FFT, HybridVFFT)
The hybrid implementation consists of an optional serial section (built using single-wire streaming FFTs) associated twiddle block, and a parallel section (implemented using the PFFT_Pipe block).
You control the length of the serial section by a user-supplied parameter. For an FFT with 2N points that processes 2M points per cycle, this parameter must be no greater than N–M.
In general, the serial section is more space-efficient; the parallel section is more multiplier-efficient. So changing the value of this parameter provides a trade-off between DSP usage and memory usage.
The HybridVFFT serial section absorbs all the variability and the size of the parallel section is fixed. The variable-size hybrid FFT includes multiple variable-size streaming FFTs, a variable-size GeneralTwiddle and a parallel FFT.
Parameter | Description |
---|---|
iFFT | true to implement an IFFT, otherwise false. |
maxsize | The maximum FFT size is 2^maxsize.HybridVFFT only. |
minsize | The minimum FFT size is 2^minsize and is limited by the value of sbits M. It cannot be smaller than 2^sbits (2^M). HybridVFFT only. |
N | Log2 of the number of points in the FFT. |
Bit-reversed input | true if you expect bit-reversed input, otherwise false. |
M | Log2 of the number of input wires. |
Number of serial stages | Length of the serial section (in radix-2 stages). |
Twiddle/pruning specification( | - |
Optimize twiddle memory usage | true to use GeneralMultTwidle (rather than GeneralTwiddle) for top-level twiddle. |
Use faithful rounding | true if the block uses faithful (rather than correct) rounding for floating-point operations. Fixed-point FFTs ignore this parameter. |
Signal | Direction | Type | Description |
---|---|---|---|
v | Input | Boolean. | Valid input signal. |
d | Input | As specified. | Complex data input signal. |
qv | Output | Boolean. | Valid output signal. |
q | Output | Determined by pruning specification. | Complex data output signal. |
size | Input | Unsigned integer | FFT serial section size, which must be at least equal to the difference between maxsize and minsize. |
Type style | Elements used |
---|---|
Bold | b |
Italic | i |
Underlined | u |