Peak Finder

Determine whether each value of input signal is local minimum or maximum

Library

Signal Operations

dspsigops

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Description

The Peak Finder block counts the number of local extrema in each column of the real-valued input signal. The block outputs the number of local extrema at the Cnt port. You can also configure the block to output the extrema indices, the extrema values, and a binary indicator of whether or not the extrema are maxima or minima.

To qualify as an extrema, a point has to be larger (or smaller) than both of its neighboring points. Thus, end points are never considered extrema.

If you select the Output peak indices check box, the Idx port appears on the block. The block outputs the extrema indices at the Idx port. If Index base is set to Zero, the block outputs zero-based extrema indices. If Index base is set to One, the block outputs one-based extrema indices.

If you select the Output peak values check box, the Val port appears on the block. The block outputs the extrema values at the Val port. If you select either of these check boxes and set the Peak type(s) to Maxima and Minima, the Pol port also appears on the block. If the signal value is a maximum, the block outputs a 1 at the Pol ("Polarity") port. If the signal value is a minimum, the block outputs a 0 at the Pol port.

Use the Maximum number of peaks to find parameter to specify how many extrema to look for in each input signal. The block stops searching the input signal once this maximum number of extrema has been found.

If you select the Ignore peaks within threshold of neighboring values check box, the block no longer detects low-amplitude peaks. This feature allows the block to ignore noise within a threshold value that you define. Enter a threshold value for the Threshold parameter. Now, the current value is a maximum if (current – previous) > threshold and (current – next) > threshold. The current value is a minimum if (current – previous) < –threshold and (current – next) < –threshold.

Examples

Example 1

Consider the input vector

[9 6 10 3 4 5 0 12]

The table below shows the analysis made by the Peak Finder block. Note that the first and last input signal values are not considered:

Previous, current, and next values	9 6 10	6 10 3	10 3 4	3 4 5	4 5 0	5 0 12
Current value if it is an extremum	6	10	3	—	5	0
Index of current value if it is an extremum	1	2	3	—	5	6
Polarity of current value if it is an extremum	0	1	0	—	1	0

For this example, the outputs at the block ports are:

Cnt: 5

Idx: [1 2 3 5 6]

Val: [6 10 3 5 0]

Pol: [0 1 0 1 0]

Example 2

The Overflow mode parameter can affect the output of the block when the input is fixed point. Consider the following model:

In this model, the settings in the Constant block are:

• Constant value — [-1 0.5 -1]

• Interpret vector parameters as 1–D — not selected

• Sampling mode — Sample based

• Sample time — 1

• Output data type — <data type expression>

• Mode — Fixed point

• Sign — Signed

• Scaling — Binary point

• Word length — 16

• Fraction length — 15

The settings in the Peak Finder blocks are:

• Peak type(s) — Maxima

• Output peak indices — not selected

• Output peak values — selected

• Maximum number of peaks to find — 2

• Ignore peaks within threshold of neighboring values — selected

• Threshold — 0.25

• Overflow mode — Wrap for Peak Finder Wrap, Saturate for Peak Finder Saturate

Setting the Overflow mode parameter of the Peak Finder Wrap block to Wrap causes the calculations (current – previous) > threshold and (current – next) > threshold to wrap on overflow, thereby causing the maximum to be missed.

Dialog Box

Parameters

Peak type(s)

Specify whether you are looking for maxima, minima, or both.

Index base

Specify the base of the extrema indices as either:

• Zero (default) –– The first index starts with 0. For example, consider an input vector [-1.5, 0.5, 0]. The peak value of this vector is 0.5 and the index of this peak value is 1.

• One –– In this setting, the first index starts with 1. The index of the peak value in [-1.5, 0.5, 0] is 2.

Output peak indices

Select this check box if you want the block to output the extrema indices at the Idx port.

Output peak values

Select this check box if you want the block to output the extrema values at the Val port.

Maximum number of peaks to find

Enter the number of extrema to look for in each input signal. The block stops searching the input signal for extrema once the maximum number of extrema has been found. The value of this parameter must be an integer greater than or equal to one.

Ignore peaks within threshold of neighboring values

Select this check box if you want to eliminate the detection of peaks whose amplitudes are within a specified threshold of neighboring values.

Threshold

Enter your threshold value. This parameter appears if you select the Ignore peaks within threshold of neighboring values check box.

When you select the Ignore peaks within threshold of neighboring values check box, the Fixed-point operational parameters section appears.

Fixed-point operational parameters

Saturate on integer overflow

When you select this parameter, the block saturates the result of its fixed-point operation. When you clear this parameter, the block wraps the result of its fixed-point operation. For details on saturate and wrap, see overflow mode for fixed-point operations.

Supported Data Types

Port	Supported Data Types
Input	Double-precision floating point Single-precision floating point Fixed point (signed and unsigned) 8-, 16-, and 32-bit signed integers 8-, 16-, and 32-bit unsigned integers
Cnt	32-bit unsigned integers
Idx	32-bit unsigned integers
Val	Double-precision floating point Single-precision floating point Fixed point (signed and unsigned) 8-, 16-, and 32-bit signed integers 8-, 16-, and 32-bit unsigned integers
Pol	Boolean

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using Simulink® Coder™.

Generated code relies on memcpy or memset functions (string.h) under certain conditions.

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