Table Of Contents

FFT (Clock-Driven Logic)

Version:
    Last Modified: January 12, 2018

    Computes the fast Fourier transform (FFT) point by point.

    To convert the output of this node to an amplitude spectrum use, use the FFT Spectrum node. To convert the output of this node to a power spectrum, use the FFT Power Spectrum and PSD node.

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    reset

    Boolean value that specifies whether to reset the internal state of the node.

    True Resets the internal state of the node.
    False Does not reset the internal state of the node.

    Behavior with Handshaking Inputs and Outputs

    The handshaking inputs and outputs on this node behave as follows during the cycles where reset is True:

    • input valid is ignored.
    • ready for output is ignored.
    • output valid is False.
    • ready for input is False, which handles cases where reset is held True for more than one cycle. This node is ready for inputs after the reset is complete and reset returns False.

    Default: False

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    data in

    Input signal for which you want to compute the FFT.

    This input accepts the following data types:

    • 8-bit signed integer
    • 8-bit unsigned integer
    • 16-bit signed integer
    • 16-bit unsigned integer
    • 32-bit signed integer
    • fixed-point numeric
    • complex fixed-point numeric

    The maximum word length for this input is 32 bits.

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    input valid

    Boolean value that describes whether the next data point has arrived for processing. Wire the output valid output of an upstream node to this input to transfer data from the upstream node to this node.

    True The next data point has arrived for processing.
    False The next data point has not arrived for processing.
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    ready for output

    Boolean value that defines whether downstream nodes are ready for this node to return a new value. Use a Feedback Node to wire the ready for input output of a downstream node to this input of the current node.

    True Downstream nodes are ready for this node to return a new value.
    False Downstream nodes are not ready for this node to return a new value.
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    Note  

    If this input is False during a cycle, the output valid output returns False during that cycle.

    Default: True

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    data out

    FFT of the input signal.

    The maximum word length for this output is 32 bits.

    Customizing the Output Data Type

    Item Complex fixed-point configurator Precision
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    data index

    Index of the FFT bin this node returns.

    Default: 0

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    output valid

    Boolean value that indicates whether this node computes a result that downstream nodes can use.

    Wire this output to input valid of a downstream node to transfer data from the node to the downstream node.

    True Downstream nodes can use the result this node computes.
    False This node returns an undefined value that downstream nodes cannot use.
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    Note  

    This node may return different undefined values when executed in simulation mode versus when executed on hardware.

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    ready for input

    Boolean value that determines whether this node is ready to accept new input data. Use a Feedback Node to wire this output to the ready for output input of an upstream node.

    True This node is ready to accept new input data.
    False This node is not ready to accept new input data.
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    Note  

    If this output returns False during a given cycle, this node discards any data that other nodes send to this node during the following cycle. This node discards the data even if the input valid input is True during the following cycle.

    Timing Diagram

    The following diagram demonstrates the timing this node uses when Throughput is equal to 1 cycle per sample.

    Where This Node Can Run:

    Desktop OS: none

    FPGA: All devices

    Web Server: Not supported in VIs that run in a web application


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