Pulse Generator

Generate square wave pulses at regular intervals

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Libraries:
Simulink / Sources

Description

The Pulse Generator block generates square wave pulses at regular intervals. The block waveform parameters, Amplitude, Pulse Width, Period, and Phase delay, determine the shape of the output waveform. The following diagram shows how each parameter affects the waveform.

The Pulse Generator block can emit scalar, vector, or matrix signals of any real data type. To emit a scalar signal, use scalars to specify the waveform parameters. To emit a vector or matrix signal, use vectors or matrices, respectively, to specify the waveform parameters. Each element of the waveform parameters affects the corresponding element of the output signal. For example, the first element of a vector amplitude parameter determines the amplitude of the first element of a vector output pulse. All the waveform parameters must have the same dimensions after scalar expansion. The data type of the output is the same as the data type of the Amplitude parameter.

The block output can be generated in time-based or sample-based modes, determined by the Pulse type parameter.

Time-Based Mode

In time-based mode, Simulink^® computes the block output only at times when the output actually changes. This approach results in fewer computations for the block output over the simulation time period. Activate this mode by setting the Pulse type parameter to Time based.

The block does not support a time-based configuration that results in a constant output signal. Simulink returns an error if the parameters Pulse Width and Period satisfy either of these conditions:

$$\begin{array}{l}Period\text{}*\frac{PulseWidth}{100}=0\\ Period\text{}*\frac{PulseWidth}{100}=Period\end{array}$$

Depending on the pulse waveform characteristics, the intervals between changes in the block output can vary. For this reason, a time-based Pulse Generator block has a variable sample time. The sample time color of such blocks is brown (see View Sample Time Information for more information).

Simulink cannot use a fixed-step solver to compute the output of a time-based pulse generator. If you specify a fixed-step solver for models that contain time-based pulse generators, Simulink computes a fixed sample time for the time-based pulse generators. Then the time-based pulse generators simulate as sample based.

If you use a fixed-step solver and the Pulse type is Time based, choose the step size such that the period, phase delay, and pulse width (in seconds) are integer multiples of the solver step size. For example, suppose that the period is 4 seconds, the pulse width is 75% (that is, 3 s), and the phase delay is 1 s. In this case, the computed sample time is 1 s. Therefore, choose a fixed-step size of 1 or a number that divides 1 exactly (for example, 0.25). To ensure this setting, select auto on the Solver pane of the Configuration Parameters dialog box.

Sample-Based Mode

In sample-based mode, the block computes its outputs at fixed intervals that you specify. Activate this mode by setting the Pulse type parameter to Sample based.

An important difference between the time-based and sample-based modes is that in time-based mode, the block output is based on simulation time, and in sample-based mode, the block output depends only on the simulation start, regardless of elapsed simulation time.

This block supports reset semantics in sample-based mode. For example, if a Pulse Generator block is in a resettable subsystem that hits a reset trigger, the block output resets to its initial condition.

Examples

Tune Phase Delay on Pulse Generator During Simulation

This example shows how to modify a model so that you can change a phase delay for a Pulse Generation block during simulation. You cannot tune the value of the Phase delay parameter during simulation. As a workaround, add a Constant block and a Variable Time Delay block.

In the Pulse Generator block, set the value of the Phase delay parameter to zero. Use the Constant block to specify the delay time in seconds. To tune the delay time during simulation, change the value stored in the Constant block.

Difference Between Time- and Sample-Based Pulse Generation

This example shows the difference in behavior of the Pulse Generator block in time-based and sample-based modes.

Consider this model, with two Pulse Generator blocks. One block has the Pulse type parameter set to Time based, and the other to Sample based. Both blocks are configured to output a pulse with an amplitude of one that is on for five seconds, followed by off for five seconds. The simulation time runs from three seconds to a stop time of 18 seconds. Notice the time offset notice in the lower right corner.

Notice that the time-based Pulse Generator produces an on signal for only two seconds and then switches to off. This is due to the block starting to compute the output from t=0 even though it does not output the simulation until t=3. The sample-based block outputs a pulse of five seconds on followed by five seconds off. In this case, the block output does not depend on simulation time and starts only when the simulation starts.

Extended Examples

Simulating Automatic Climate Control Systems

Simulate an automatic climate control system in a car using Simulink® and Stateflow®.

• Open Model

Bang-Bang Control Using Temporal Logic

Use Stateflow® to model a bang-bang temperature control system for a boiler. The boiler dynamics are modeled in Simulink®.

• Open Model

Ports

Output

Port_1 — Output signal

scalar | vector | matrix

Generated square wave pulse signal specified by the parameters.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | fixed point

Parameters

Pulse type — Computational technique

Time based (default) | Sample based

Computational technique to generate the type of square wave that this block generates, either time- or sample-based. Some parameters in the dialog box appear depending on whether you select time-based or sample-based.

Programmatic Use

Block Parameter: PulseType

Type: character vector

Values: 'Time based' | 'Sample based'

Default: 'Time based'

Time (t) — Source of time variable

Use simulation time (default) | Use external signal

Specifies whether to use simulation time or an external signal as the source of values for the output pulse's time variable. If you specify an external source, the block displays an input port for connecting the source. The output pulse differs as follows:

• Use simulation time: The block generates an output pulse where the time variable equals the simulation time.

• Use external signal: The block generates an output pulse where the time variable equals the value from the input port, which can differ from the simulation time.

Programmatic Use

Block Parameter: TimeSource

Type: character vector

Values: 'Use simulation time' | 'Use external signal'

Default: 'Use simulation time'

Amplitude — Signal amplitude

1 (default) | scalar

Specify the amplitude of the signal.

Programmatic Use

Block Parameter: Amplitude

Type: character vector

Value: scalar

Default: '1'

Period (secs) — Pulse period

10 (default) | scalar

Pulse period specified in seconds if the pulse type is time-based. If the pulse type is sample-based, then the period is specified as the number of sample times.

Programmatic Use

Block Parameter: Period

Type: character vector

Value: scalar

Default: '10'

Pulse width — Duty cycle

5 (default) | scalar in the range [0,100]

Duty cycle specified as the percentage of the pulse period that the signal is on if time-based or as number of sample times if sample-based.

Programmatic Use

Block Parameter: PulseWidth

Type: character vector

Value: scalar

Default: '5'

Phase delay (secs) — Delay before pulse

0 (default) | scalar

Delay before the pulse is generated, specified in seconds, if the pulse type is time-based or as number of sample times if the pulse type is sample-based.

Programmatic Use

Block Parameter: PhaseDelay

Type: character vector

Value: scalar

Default: '0'

Sample time — Length of sample time

0 (default) | scalar | vector

Length of the sample time for this block in seconds. This parameter appears only if the block's pulse type is sample-based. See Specify Sample Time.

Programmatic Use

Block Parameter: SampleTime

Type: character vector

Value: scalar

Default: '1'

Interpret vector parameters as 1-D — Treat vectors as 1-D

on (default) | off

Select this check box to output a vector of length N if the Amplitude, Period, Pulse width, or Phase delay parameter evaluates to an N-element row or column vector.

• When you select this check box, the block outputs a vector of length N if any of the value parameters evaluate to an N-element row or column vector. For example, the block outputs a matrix of dimension 1-by-N or N-by-1.

• When you clear this check box, the block does not output a vector of length N if any of the value parameters evaluate to an N-element row or column vector.

For more information on how this parameter is used, see Determine the Output Dimensions of Source Blocks.

Programmatic Use

Block Parameter: VectorParams1D

Type: character vector

Values: 'on' | 'off'

Default: 'on'

Block Characteristics

Data Types	Boolean | double | fixed point | integer | single
Direct Feedthrough	yes
Multidimensional Signals	no
Variable-Size Signals	no
Zero-Crossing Detection	no

Extended Capabilities

C/C++ Code Generation

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

Cannot be used inside a triggered subsystem hierarchy.

These blocks do not reference absolute time when configured for sample-based operation. In time-based operation, they depend on absolute time.

HDL Code Generation

Generate VHDL, Verilog and SystemVerilog code for FPGA and ASIC designs using HDL Coder™.

HDL code generation is supported for this block with the Pulse type parameter set to Sample based and the Time (t) parameter set to Use simulation time.

PLC Code Generation
Generate Structured Text code using Simulink® PLC Coder™.

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

Version History

Introduced before R2006a