Table Of Contents

Filter Order Estimation (Inverse Chebyshev) (G Dataflow)

Version:
    Last Modified: January 9, 2017

    Estimates the Inverse Chebyshev filter order.

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    filter type

    The type of filter that this node estimates.

    Name Description
    Lowpass

    Estimates a lowpass filter.

    Highpass

    Estimates a highpass filter.

    Bandpass

    Estimates a bandpass filter.

    Bandstop

    Estimates a bandstop filter.

    Default: Lowpass

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    frequency specifications

    Band edge frequencies of the filter, in Hz.

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    lower pass frequency

    First passband edge frequency in Hz.

    Default: 0.2

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    lower stop frequency

    First stopband edge frequency in Hz.

    Default: 0.3

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    higher pass frequency

    Second passband edge frequency in Hz. The node ignores this input for lowpass and highpass filters.

    Default: 0

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    higher stop frequency

    Second stopband edge frequency, in Hz. The node ignores this input for lowpass and highpass filters.

    Default: 0

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    ripple specifications

    Ripple level in the passband and stopband of the filter.

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    passband

    Ripple level in the passband.

    Default: 0.1

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    stopband

    Ripple level in the stopband.

    Default: 60

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    dB?

    A Boolean value that specifies whether this node applies a decibel scale or a linear scale to the ripple levels.

    True The node applies a decibel scale to the ripple level.
    False The node applies a linear scale to the ripple level.

    Default: True

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    error in

    Error conditions that occur before this node runs. The node responds to this input according to standard error behavior.

    Default: No error

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    sampling frequency

    The sampling frequency in Hz.

    This value must be greater than zero.

    Default: 1.0 Hz, which is the normalized sampling frequency

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    estimated order

    Minimum order value that the filter requires to meet the specifications you set.

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    low cutoff frequency

    Low cutoff frequency. The cutoff frequency corresponds to the edge frequency of the stopband.

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    high cutoff frequency

    High cutoff frequency. The cutoff frequency corresponds to the edge frequency of the stopband.

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    error out

    Error information. The node produces this output according to standard error behavior.

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    stopband attenuation

    Stopband attenuation in decibels.

    Algorithm for Inverse Chebyshev Order Estimation

    This node uses the following equations to estimate the order of an Inverse Chebyshev filter:

    N = acosh ( ε s / ε p ) acosh ( Ω s / Ω p )
    ε p = 10 A p / 10 1
    ε s = 10 A s / 10 1
    where
    • N is the estimated order
    • Ap is the passband ripple in dB
    • As is the stopband ripple in dB
    • means Round Toward + Infinity

    The following table lists the equations for calculating Ω p and Ω s for different types of filters:

    Lowpass filter

    Ω p = Ω p 1

    Ω s = Ω s 1

    Highpass filter

    Ω p = 1 / Ω p 1

    Ω s = 1 / Ω s 1

    Bandpass filter

    Ω p = Ω p 2 Ω p 1

    Ω s = min ( | Ω s 1 Ω p 1 Ω p 2 Ω s 1 | , | Ω s 2 Ω p 1 Ω p 2 Ω s 2 | )

    Bandstop filter

    Ω p = max ( | 1 Ω p 1 Ω s 1 Ω s 2 Ω p 1 | , | 1 Ω p 2 Ω s 1 Ω s 2 Ω p 2 | )

    Ω s = 1 Ω s 2 Ω s 1

    where the various Ω values equal as follows:

    Ω p 1 = tan ( π * lower pass frequency sampling frequency )
    Ω p 2 = tan ( π * higher pass frequency sampling frequency )
    Ω s 1 = tan ( π * lower stop frequency sampling frequency )
    Ω s 2 = tan ( π * higher stop frequency sampling frequency )

    Where This Node Can Run:

    Desktop OS: Windows

    FPGA: Not supported


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