Unified FFT Intel® FPGA IPs User Guide

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ID 683366
Date 6/17/2024
Public
Document Table of Contents
Document Table of Contents x
1. About the Unified FFT Intel FPGA IPs 2. Getting Started with the Unified FFT Intel FPGA IP 3. Bit-reverse Intel® FPGA IP 4. FFT Intel FPGA IP 5. Parallel FFT Intel FPGA IP 6. Variable Size Bit-reverse Intel FPGA IP 7. Variable Size FFT Intel FPGA IP 8. Unified FFT Intel FPGA IPs User Guide Archive 9. Document Revision History for the Unified FFT Intel FPGA IPs User Guide
1. About the Unified FFT Intel FPGA IPs x
1.1. Features of the Unified FFT Intel FPGA IPs 1.2. Unified FFT Intel FPGA IPs Device Family Support 1.3. Release Information for the Unified FFT IPs 1.4. Supported Data Types 1.5. FFT Spectrum 1.6. Global Enable
2. Getting Started with the Unified FFT Intel FPGA IP x
2.1. Installing and Licensing Intel® FPGA IP Cores 2.2. Generating a Unified FFT IP 2.3. Compiling the Software Model for the Unified FFT IPs 2.4. Running the Unified FFT IPs Automatic Testbench
1. About the Unified FFT Intel FPGA IPs
2. Getting Started with the Unified FFT Intel FPGA IP
3. Bit-reverse Intel® FPGA IP
4. FFT Intel FPGA IP
5. Parallel FFT Intel FPGA IP
6. Variable Size Bit-reverse Intel FPGA IP
7. Variable Size FFT Intel FPGA IP
8. Unified FFT Intel FPGA IPs User Guide Archive
9. Document Revision History for the Unified FFT Intel FPGA IPs User Guide

7. Variable Size FFT Intel FPGA IP

The IP performs variable size streaming FFT and inverse FFT operations. You can dynamically specify the size of the current FFT. You must completely flush the previous FFT out of the FFT pipeline before changing the size of the FFT.
Table 15.  Variable Size FFT Intel FPGA IP Input Signals
Name Description
clk All input signals must be synchronous to this clock.
rst

Reset signals.

The reset signal is asynchronous for Arria® 10 and Cyclone® 10 GX device; synchronous for Agilex™ 5, Agilex™ 7, and Stratix® 10.

If the reset is asynchronous, deassert the reset signal synchronously to the input clock to avoid metastability issues.

Select the reset polarity with the Reset polarity parameter.

validIn

Data valid signal. Assert this signal when input data is valid.

This signal must not deassert during an FFT. Keep it asserted from the first input to last input of an FFT.

channelIn Not used. Connect it to ground.
d

Data input signal.

This signal contains the complex data, size of the FFT, and the optional enable. The size of the FFT is represented as a logarithm to base 2. For example, a value of 2 represents a 4-point FFT and 16 represents a 64K-point FFT.

The signal order is from least significant bit (LSB) to most significant bit (MSB):

  1. Real data input
  2. Imaginary data input
  3. Size of the current FFT
  4. Global enable input (if requested)
Table 16.  Variable Size FFT Intel FPGA IP Output Signals
Name Description
validOut Data valid signal. The IP asserts this signal for valid output data.
channelOut Not used.
q

Data output signal.

This signal contains complex data and size of the FFT. The size of the FFT is represented as a logarithm to base 2. For example, a value of 2 represents a 4 point FFT and 16 represents a 64K point FFT. The signals are in the following order from LSB to MSB:

  1. Real output
  2. Imaginary output
  3. Size of the current FFT
The size output is the specified input size that the IP delays appropriately to synchronize with the output data.
Table 17.  Variable Size FFT Intel FPGA IP Parameters
Parameter Value Description
Core Parameters
Inverse FFT -

Specify if the operation is an FFT or inverse FFT.

Turn on for an inverse FFT; turn off to compute a normal FFT.
Bit-reversed input

Specify if the input is in natural or bit-reversed order.

Turn on for the IP to receive its input in bit-reversed order and to produce its output in natural order. Turn off for the IP to receive its input in natural order and to produce its output in bit-reversed order.

You can use the Variable Size Bit-reverse Intel FPGA IP to bit-reverse the input or the output.
Log2(Minimum Size) 0 to 16

Specify minimum the size of the FFT.

For example, a value of 0 represents a 1 point FFT and 16 represents a 64K point FFT.
Log2(Maximum Size) 2 to 16

Specify the maximum size of the FFT.

For example, a value of 2 represents a 4 point FFT and 16 represents a 64K point FFT.
Datatypes

Fixed Point

Floating Point

 Select a fixed-point or floating-point FFT.
Floating point types

Single

Double

Custom

Select a floating-point format.

Only available when Datatypes is Floating Point.

Reset polarity

Active High

Active Low

 Select the reset polarity.
Signal Widths
Input width 4 to 32

Specify the width of the complex data input in bits.

The input is a complex value. The IP applies the Input width separately to the real and imaginary components of the complex signal. The total width of the complex signal is double the value of this parameter.

Only available when Datatypes is Fixed Point.

Twiddle width 4 to 32

Specify the width of the twiddle constants.

The twiddle constants are complex values. The IP applies the Twiddle width separately to the real and imaginary components of the complex signal. The total width of the complex signal is double the value of this parameter.

Exponent width 5 to 11

Specify the width of the floating point exponent.

Only available when Floating point type is Custom.

Mantissa width 7 to 52

Specify the width of the floating-point mantissa.

Only available when Floating point type is Custom.

Twiddle Parameters
Pruning scheme

Full Wordgrowth

Mild Pruning

Prune To Width

Select the pruning scheme.

Each pruning scheme has a different effect on the datapath:

  • Full wordgrowth allows the datapath to grow by one bit at each adder, and at the first multiplier.
  • Mild pruning allows the datapath to grow by one bit at each adder, and at the first multiplier. It also reduces its width by one bit immediately before each multiplier.
  • Prune to width allows the datapath to grow by one bit at each adder, and at the first multiplier. It also reduces its width to be no more than the specified Pruning width immediately before each multiplier.

Whenever pruning is applied to the datapath only the least significant bit(s) of the datapath are removed.

The IP determines the resultant scaling of the output by the maximum size of the FFT and not the current dynamic size. All FFT sizes within the range you specify pass through the same (maximum) number of pruning stages.

Only available when Datatypes is Fixed Point.

Pruning width 4 to 32

Specify the pruning width. The IP applies the Pruning width separately to the real and imaginary components of the complex signal.

Only available when Pruning scheme is set to Prune To Width.

Generation Parameters
Generate a global enable signal - Select to generate a global enable signal, which you can use to enable and disable the IP. This enable doesn't force the output valid signal to go low.
Generate a software model - Select to generate a software model of the IP in C++ language.
Generate a cycle-accurate software model -

Select to generate a cycle-accurate software model. If this option is not selected the generated software model is not cycle accurate with respect to RTL of the IP.

Only available when you select Generate a software model .

Generate HLD external function wrappers -

Select to generate wrapper files so that you can use the IP as an external function with HLD tools such as HLS and OpenCL.

Only available if generating a software model.
Frequency target 20 to 2000

Specify the frequency at which the IP is required to operate in MHz.

The Frequency target affects the RTL generation for that IP.

Device family -

Specifies the device family the IP is targeting.

Usually, the Intel Quartus project sets this value. If using other tools such as qsys-generate, refer to those tools’ documentation.

The Device family affects the RTL generation for that IP.

Speed grade -

Specifies the speed grade of the device the IP is required to operate on.

Usually, the Intel Quartus project sets this value. If using other tools such as qsys-generate, refer to those tools’ documentation.

The Speed grade affects the RTL generation for that IP.

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