Simulink^®

Discrete FIR Filter - Model FIR filters

Library

Discrete

Description

The Discrete FIR Filter block independently filters each channel of the input signal with the specified digital FIR filter. The block can implement static filters with fixed coefficients, as well as time-varying filters with coefficients that change over time. You can tune the coefficients of a static filter during simulation.

This block filters each channel of the input signal independently over time, treating each element of the input as an individual channel. The output dimensions are always the same as those of the input signal that is filtered, except in single-input/multi-output mode.

The outputs of this block numerically match the outputs of the Signal Processing Blockset™ Digital Filter Design block and of the Signal Processing Toolbox™ dfilt function.

This block supports the Simulink^® state logging feature. See States in the Simulink User's Guide for more information.

Specifying Initial States

The Discrete FIR Filter block initializes the internal filter states to zero by default, which is equivalent to assuming that past inputs and outputs are zero. You can optionally use the Initial states parameter to specify nonzero initial conditions for the filter delays.

To determine the number of initial states you must specify and how to specify them, see the table on valid initial states. The Initial states parameter can take one of the forms described in the next table.

Valid Initial States

Initial Condition Description

Initial Condition	Description
Scalar	The block initializes all delay elements in the filter to the scalar value.
Vector or matrix (for applying different delay elements to each channel)	Each vector or matrix element specifies a unique initial condition for a corresponding delay element in a corresponding channel: The vector length must be equal to the product of the number of input channels and the number of delay elements in the filter, `#_of_filter_coeffs-1`. The matrix must have the same number of rows as the number of delay elements in the filter, `#_of_filter_coeffs-1`, and must have one column for each channel of the input signal.

Scalar

The block initializes all delay elements in the filter to the scalar value.

Vector or matrix
(for applying different delay elements to each channel)

Each vector or matrix element specifies a unique initial condition for a corresponding delay element in a corresponding channel:

The vector length must be equal to the product of the number of input channels and the number of delay elements in the filter, #_of_filter_coeffs-1.
The matrix must have the same number of rows as the number of delay elements in the filter, #_of_filter_coeffs-1, and must have one column for each channel of the input signal.

Data Type Support

The Discrete FIR Filter block accepts and outputs real and complex signals of any data type supported by Simulink except Boolean. The same types are supported for the numerator coefficients. The input states have the same data type as the block input.

The following diagrams show the filter structure and the data types used within the Discrete FIR Filter block for fixed-point signals.

Parameters and Dialog Box

The Main pane of the Discrete FIR Filter block dialog appears as follows.

Coefficient source

Specify whether you want to input the filter coefficients on the block mask or inherit them from an input port.

Numerator coefficient

Specify the vector of numerator coefficients of the filter's transfer function.

This parameter is only visible when Dialog parameters is selected for the Coefficient source parameter.

Initial states

Specify the initial conditions of the filter states. To learn how to specify initial states, see Specifying Initial States.

Sample time (-1 for inherited)

Specify the time interval between samples. To inherit the sample time, set this parameter to -1. See Specifying Sample Time.

The Fixed-point pane of the Discrete FIR Filter block dialog appears as follows.

Coefficient minimum

Specify the minimum value that a filter coefficient should have. The default value, [], is equivalent to -Inf. Simulink software uses this value to perform:

Parameter range checking (see Checking Parameter Values)
Automatic scaling of fixed-point data types

Coefficient maximum

Specify the maximum value that a filter coefficient should have. The default value, [], is equivalent to Inf. Simulink software uses this value to perform:

Parameter range checking (see Checking Parameter Values)
Automatic scaling of fixed-point data types

Output minimum

Specify the minimum value that the block should output. The default value, [], is equivalent to -Inf. Simulink software uses this value to perform:

Simulation range checking (see Checking Signal Ranges)
Automatic scaling of fixed-point data types

Output maximum

Specify the maximum value that the block should output. The default value, [], is equivalent to Inf. Simulink software uses this value to perform:

Simulation range checking (see Checking Signal Ranges)
Automatic scaling of fixed-point data types

Coefficient data type

Specify the coefficient data type. You can set it to:

A rule that inherits a data type, for example, Inherit: Same word length as input
A built-in integer, for example, int8
A data type object, for example, a Simulink.NumericType object
An expression that evaluates to a data type, for example, fixdt(1,16,0)

Click the Show data type assistant button to display the Data Type Assistant, which helps you set the Coefficient data type parameter.

See Using the Data Type Assistant for more information.

Product output data type

Specify the product output data type. You can set it to:

A rule that inherits a data type, for example, Inherit: Inherit via internal rule
A built-in data type, for example, int8
A data type object, for example, a Simulink.NumericType object
An expression that evaluates to a data type, for example, fixdt(1,16,0)

Click the Show data type assistant button to display the Data Type Assistant, which helps you set the Product output data type parameter.

See Using the Data Type Assistant for more information.

Accumulator data type

Specify the accumulator data type. You can set it to:

A rule that inherits a data type, for example, Inherit: Same as product output
A built-in data type, for example, int8
A data type object, for example, a Simulink.NumericType object
An expression that evaluates to a data type, for example, fixdt(1,16,0)

Click the Show data type assistant button to display the Data Type Assistant, which helps you set the Accumulator data type parameter.

See Using the Data Type Assistant for more information.

Output data type

Specify the output data type. You can set it to:

A rule that inherits a data type, for example, Inherit: Same as accumulator
A built-in data type, for example, int8
A data type object, for example, a Simulink.NumericType object
An expression that evaluates to a data type, for example, fixdt(1,16,0)

Click the Show data type assistant button to display the Data Type Assistant, which helps you set the Output data type parameter.

See Specifying Block Output Data Types for more information.

Lock output scaling against changes by the autoscaling tool

Select to lock scaling of outputs.

Round integer calculations toward

Select the rounding mode for fixed-point operations.

Saturate on integer overflow

Select to have overflows saturate. Otherwise, they wrap.

Characteristics

Direct Feedthrough	Yes
Sample Time	Specified in the Sample time parameter
Scalar Expansion	Yes, of initial states
States	See Specifying Initial States
Dimensionalized	Yes
Zero Crossing	No

Discrete Filter

Discrete State-Space