SIMPLIS Parts

Digital Signal Source

The Digital Signal Source provides a flexible way to define digital circuit stimulus. For simple signals, a parameter editing dialog may be used, and for complex signal definitions, a simple tab separated ASCII text file can be used. The digital signal source can have between 1 and 32 output pins.

For single bit periodic sources, such as clocks, see the Digital Pulse Source.

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Model Name:

Digital Signal Source

Simulator:

This device is compatible with the SIMPLIS simulator.

Parts Selector
Menu Location:

Digital Functions | Sources

Symbol Library:

None - the symbol is automatically generated when placed or edited.

Model File:

None - the device model is generated before simulation.

Subcircuit Name:
  • SIMPLIS_DIGI1_D_SIGNAL_SOURCE_N: Without Ground Reference
  • SIMPLIS_DIGI1_D_SIGNAL_SOURCE_Y: With Ground Reference

Symbol:

Multiple Selections:

Only one device at a time can be edited.

Editing the Digital Signal Source

To configure the Digital Signal Source, double click on the symbol to open the parameter editing dialog:

Label Parameter Description

Number of Output Bits

Number of output bits for the digital signal source

Ground Ref

Determines whether or not a device has a ground reference pin.

Any digital component that has an input or output pin connected to an analog circuit node must have its Ground Ref pin connected to an analog node. This is usually ground on the schematic. For more information on the use of Ground Ref for digital components, see When is Ground Ref Required?

Redefine Source?

Determines whether the source is to be redefined after the dialog is closed.

  • Checked: The source will be redefined after the dialog is closed.
  • Unchecked: The source definition remains unchanged after the dialog is closed.

Source Definition Method

Determines whether the definition of the digital signal source comes from a dialog or an external file.

If Redefine Source? is checked, you will be prompted to edit the digital signal source definition with a dialog or to choose a new definition file, depending on the value of Source Definition Method after this dialog is closed.

Clicking on the   Interface   tab displays the Analog - Digital interface parameters:

Label Parameter Description

Output Resistance

Output resistance of the digital signal source output pin(s).

Output High Voltage

Output high voltage for the digital signal source output pin(s).

Output Low Voltage

Output low voltage for the digital signal source output pin(s).

Table Definition Methods

The Digital Signal Source can be defined with a dialog, or with a points file.

Dialog Method

Using the dialog method, the points definition is saved to a property on the Digital Signal Source symbol. This method is often used for small source definitions. You can define up to 255 logical input states with the dialog method.

To define the source with this method, check the Redefine Source? Checkbox and select dialog in the Source Definition Method box. After closing the main dialog, a table editing dialog will appear.

File Method

Using the file method, the points definition is saved as a plain ASCII text file, and before the simulation starts, the points file is read in and used to configure the source. This method is often used for large or complicated source definitions, although you can use this method for any size table.

The source used in the SIMPLIS Lookup Table with Don't Care Input Definitions example is used to demonstrate the fie format. The file method uses whitespace, including tabs and spaces to delimit columns in the points definition file. Lines starting with the asterisk (*) are considered comments and are ignored. The Time is defined in the first column. The states for each output pin follow in MSB -> LSB order, and since these are single bits, the output states are defined as either 0 or 1. The example table has five columns, one for the time and four for the output bits.
Source Definition

Any number of points can be defined using the file method.

An example points definition file can be downloaded here : simplis_040_digitalsignalsource.txt. This file is also included in the zip archive of the example files simplis_040_digitalsignalsource_example.zip.

Common File Formatting Issues

The file definitions for the Digital Signal Source and the Digital Lookup Tables are read into SIMPLIS by the same block of code. The errors in input file syntax are therefore similar. A description of the most common errors in input file formatting can be found here: Common File Formatting Issues

Examples

The test circuit used to generate the waveform examples in the next section can be downloaded here: simplis_040_digitalsignalsource_example.zip.

Waveforms

The waveforms below were taken from the state machine example described in the SIMPLIS Lookup Table with Don't Care Input Definitions.

Subcircuit Parameters

The Digital Signal Source model is generated by a template script when the simulation is executed. For this reason, there is no fixed model which can be inserted into a netlist. The template script for this device is simplis_make_signal_source_model.sxscr, and can be downloaded as part of a zip archive of all built-in scripts from the SIMetrix website.