Allpole Filter

Model allpole filters

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Libraries:
DSP System Toolbox / Filtering / Filter Implementations

Description

The Allpole Filter block independently filters each channel of the input signal with the specified allpole filter. The block can implement static filters with fixed coefficients and 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. The Input processing parameter allows you to specify whether the block treats each element of the input as an independent channel (sample-based processing), or each column of the input as an independent channel (frame-based processing).

This block supports the Simulink^® state logging feature. See State (Simulink) for more information.

Examples

Estimate Transfer Function in Simulink

To estimate the transfer function of a system in Simulink®, use the Discrete Transfer Function Estimator block. The block implements the Welch's average modified periodogram method and uses the measured input and output data for estimation.

• Open Model

Ports

Input

In — Data input

vector | matrix

Specify the data input as a vector or a matrix. The block accepts variable-size inputs. During simulation, you can change the size of each input channel, but the number of channels must remain the same.

The data input and the filter coefficients must have the same data type.

If the input is fixed point, it must be a signed integer or a signed fixed point value with a power-of-two slope and zero bias.

This port is unnamed until you set Coefficient source to Input port.

Data Types: single | double | int8 | int16 | int32 | fixed point
Complex Number Support: Yes

Den — Filter denominator coefficients

scalar | row vector

Specify the denominator coefficients of the filter transfer function as a scalar or a row vector. The data input and the filter coefficients must have the same data type.

Dependencies

To enable this port, set Coefficient source to Input port.

Data Types: single | double | int8 | int16 | int32 | fixed point
Complex Number Support: Yes

Output

Out — Filtered output

vector | matrix

Filtered output, returned as a vector or a matrix. The size, data type, and complexity of the output signal matches that of the input signal.

This port is unnamed until you set Coefficient source to Input port.

Data Types: single | double | int8 | int16 | int32 | fixed point
Complex Number Support: Yes

Parameters

Main Tab

Coefficient source — Coefficient source

Dialog parameters (default) | Input port

Select whether you want to specify the filter coefficients in the block mask or through an input port.

Filter structure — Specify filter structure

Direct form (default) | Direct form transposed | Lattice AR

Specify the filter structure as one of these:

• Direct form

• Direct form transposed

• Lattice AR

The block does not support analysis methods for fixed-point processing if you specify the structure as Direct form or Direct form transposed.

Coefficients — Filter denominator coefficients

[1 0.1] (default) | scalar | row vector

Specify the denominator coefficients of the filter transfer function as a scalar or a row vector.

Tunable: Yes

Dependencies

To enable this parameter, set Coefficient source to Dialog parameters.

Input processing — Input processing

Columns as channels (frame based) (default) | Elements as channels (sample based)

Specify whether the block performs sample- or frame-based processing. You can select one of the following options:

• Columns as channels (frame based) — Treat each column of the input as an independent channel (frame-based processing).

• Elements as channels (sample based) — Treat each element of the input as an independent channel (sample-based processing).

Initial states — Initial conditions of filter states

0 (default) | scalar | vector | matrix

Specify the initial conditions of the filter states as a scalar, vector, or a matrix.

The Allpole Filter block initializes the internal filter states to zero by default, which has the same effect as assuming that past inputs and outputs are zero. You can optionally use this 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 this table.

Valid Initial States

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 equals the product of the number of input channels and the number of delay elements in the filter, #_of_filter_coeffs-1 (or #_of_reflection_coeffs for Lattice AR). The matrix must have the same number of rows as the number of delay elements in the filter, #_of_filter_coeffs-1 (#_of_reflection_coeffs for Lattice AR), and must have one column for each channel of the input signal.

Data Types Tab

Coefficients — Coefficient data type

Inherit: Same word length as input (default) | int8 | uint8 | int16 | uint16 | int32 | uint32 | int64 | uint64 | fixdt(1,16) | fixdt(1,16,0)

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 Coefficients parameter.

See Specify Data Types Using Data Type Assistant (Simulink) for more information.

Coefficients Minimum — Minimum value of filter coefficients

[] (default) | scalar

Specify the minimum value of the filter coefficients. The default value is [] (unspecified). Simulink software uses this value to perform:

• Parameter range checking (see Specify Minimum and Maximum Values for Block Parameters (Simulink))

• Automatic scaling of fixed-point data types

Coefficients Maximum — Maximum value of filter coefficients

[] (default) | scalar

Specify the maximum value of the filter coefficients. The default value is [] (unspecified). Simulink software uses this value to perform:

• Parameter range checking (see Specify Minimum and Maximum Values for Block Parameters (Simulink))

• Automatic scaling of fixed-point data types

Product output — Product output data type

Inherit: Inherit via internal rule (default) | Inherit: Same as input | int8 | uint8 | int16 | uint16 | int32 | uint32 | int64 | uint64 | fixdt(1,16,0)

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. For more information on this rule, see 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 parameter.

See Specify Data Types Using Data Type Assistant (Simulink) for more information.

Accumulator — Accumulator data type

Inherit: Inherit via internal rule (default) | Inherit: Same as input | Inherit: Same as product output | int8 | uint8 | int16 | uint16 | int32 | uint32 | int64 | uint64 | fixdt(1,16,0)

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

• A rule that inherits a data type, for example, Inherit: Inherit via internal rule. For more information on this rule, see 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 Accumulator parameter.

See Specify Data Types Using Data Type Assistant (Simulink) for more information.

State — State data type

Inherit: Same as accumulator (default) | Inherit: Same as input | int8 | uint8 | int16 | uint16 | int32 | uint32 | int64 | uint64 | fixdt(1,16,0)

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

• A rule that inherits a data type, for example, Inherit: Same as accumulator

• 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 State parameter.

See Specify Data Types Using Data Type Assistant (Simulink) for more information.

Dependencies

To enable this parameter, set Filter structure to Lattice AR.

Output — Output data type

Inherit: Same as input (default) | Inherit: Same as accumulator | int8 | uint8 | int16 | uint16 | int32 | uint32 | int64 | uint64 | fixdt(1,16) | fixdt(1,16,0)

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 parameter.

See Control Data Types of Signals (Simulink) for more information.

Output Minimum — Output minimum

[] (default) | scalar

Specify the minimum value that the block must output. The default value is [] (unspecified). Simulink software uses this value to perform:

• Simulation range checking (see Specify Signal Ranges (Simulink))

• Automatic scaling of fixed-point data types

Output Maximum — Output maximum

[] (default) | scalar

Specify the maximum value that the block must output. The default value is [] (unspecified). Simulink software uses this value to perform:

• Simulation range checking (see Specify Signal Ranges (Simulink))

• Automatic scaling of fixed-point data types

Lock data type settings against changes by the fixed-point tools — Prevent fixed-point tools from overriding data types

off (default) | on

Select this parameter to prevent the fixed-point tools from overriding the data types you specify in the block dialog box.

Integer rounding mode — Integer rounding mode

Floor (default) | Ceiling | Convergent | Nearest | Round | Simplest | Zero

Specify the rounding mode for fixed-point operations.

Saturate on integer overflow — Saturate on integer overflow

off (default) | on

When you select this check box, the block applies saturation to every internal operation and not just the output or result. In general, the code generation process can detect when overflow is not possible. In this case, the code generator does not produce saturation code.

Action	Reasons for Taking This Action	What Happens for Overflows	Example
Select this check box.	Your model has possible overflow and you want explicit saturation protection in the generated code.	Overflows saturate to either the minimum or maximum value that the data type can represent.	An overflow associated with a signed 8-bit integer can saturate to -128 or 127.
Do not select this check box.	You want to optimize efficiency of your generated code. You want to avoid overspecifying how a block handles out-of-range signals. For more information, see Troubleshoot Signal Range Errors (Simulink).	Overflows wrap to the appropriate value that is representable by the data type.	The number 130 does not fit in a signed 8-bit integer and wraps to -126.

Block Characteristics

Data Types	double | fixed pointa | integera | single
Direct Feedthrough	no
Multidimensional Signals	no
Variable-Size Signals	yes
Zero-Crossing Detection	no
a This block only supports signed fixed-point data types.

More About

Filter Structure Diagrams

These diagrams show the filter structure and the data types used within the Allpole Filter block for fixed-point signals.

Direct Form

You cannot specify the state data type on the block mask for this structure because the output states have the same data types as the output.

Direct Form Transposed

States are complex when either the inputs or the coefficients are complex.

Lattice AR

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Fixed-Point Conversion
Design and simulate fixed-point systems using Fixed-Point Designer™.

Version History

Introduced in R2011b