Digital Comparator

The Digital Comparator compares two digital buses and outputs the comparison results on the five output pins. The device outputs the five combinatorial possibilities, allowing the user to easily see the results of the comparison. The bus inputs can have between 2 and 32 bits, and can be formatted as unsigned, offset binary, or two's complement.

For a comparator with analog inputs and digital outputs, see the Comparator with Analog Inputs and Digital Outputs topic.

In this topic:

Model Name: Digital Comparator
Simulator: This device is compatible with the SIMPLIS simulator.
Parts Selector Menu Location: Digital Functions > Functions
Symbol Library: None - the symbol is automatically generated when placed or edited.
Model Library: None - the model is automatically generated when the simulation is run.
Subcircuit Names:
  • SIMPLIS_DIGI1_D_D_COMPARATOR_N : Without Ground Reference
  • SIMPLIS_DIGI1_D_D_COMPARATOR_Y : With Ground Reference
Symbol:
3-bit without Ground Reference
Multiple Selections: Only one device at a time can be edited.

Editing the Digital Comparator

To configure the Digital Comparator, follow these steps:

  1. Double click the symbol on the schematic to open the editing dialog to the Parameters tab.
  2. Make the appropriate changes to the fields described in the table below the image.
Label Parameter Description
Propagation Delay Delay from when the input state changes until the output changes
Number of Bits Number of input bits to the Digital Comparator
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 the ground on the schematic.
Code Encoding scheme for binary inputs/outputs for the Digital Comparator
Initial Condition Initial condition of the Digital Comparator output at time=0

To define the parameters for the interface between this digital component and each analog component connected directly to an input or output pin, follow these steps:

  1. From the Edit Digital Comparator dialog box, click on the Interface tab.
  2. Make the appropriate changes to the fields described in the table below the image.
Label Parameter Description
Input Resistance Input resistance of each Digital Comparator input pin
Hysteresis, Threshold Hysteresis and Threshold of the inputs. The hysteretic-window width, HYSTWD is centered around Threshold (TH) voltage. To determine the actual threshold ( TL , THI ), substitute Threshold (TH) and Hysteresis (HYSTWD) in each of the following formulas:
Input Logic Level Actual Threshold
1 Threshold + 0.5 * Hysteresis
0 Threshold - 0.5 * Hysteresis
Output Resistance Output resistance of each Digital Comparator output pin
Output High Voltage Output high voltage for each Digital Comparator output pin
Output Low Voltage Output low voltage for each Digital Comparator output pin

Examples

An example using the Digital Comparator is a up/down counter with programmable limits. This example is described in the Other Counters.

Subcircuit Parameters

Because the Digital Comparator model is generated by a template script when the simulation is executed, a hand-coded model cannot be inserted into a netlist. The template script for this device is simplis_make_adder_model.sxscr, which licensed users can download as part of a zip archive of all built-in scripts.

To download the zip archive, follow these steps:

Important: You will be prompted to log in with the user name and password you received with your license file. If you don't have the user name and password, you can email support@simplistechnologies.com with your license information to receive the login credentials. Include a screenshot of the dialog which opens when you run the Help > License Diagnostics... menu.
  1. Click http://www.simetrix.co.uk/simetrix80/scripts.zip to download the script archive.
  2. Enter the user name and password you received with your license file.

The following parameter table defines the parameters used in this model.

Parameter Name Label Data Type Range Units Parameter Description
CODE Code String
  • 'UNSIGNED'
  • 'TWOS_COMPLEMENT'
  • 'OFFSET_BINARY'
 none Encoding scheme for binary inputs/outputs for the Digital Comparator
GNDREF Ground Ref String
  • 'Y'
  • 'N'
 none 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 the ground on the schematic.
HYSTWD,
TH		 Hysteresis,
Threshold		 Number min: 1f V Hysteresis and Threshold of the inputs. The hysteretic-window width, HYSTWD is centered around Threshold (TH) voltage. To determine the actual threshold ( TL , THI ), substitute Threshold (TH) and Hysteresis (HYSTWD) in each of the following formulas:
Input Logic Level Actual Threshold
1 Threshold + 0.5 * Hysteresis
0 Threshold - 0.5 * Hysteresis
IC Initial Condition Number
  • 0
  • 1
 none Initial condition of the Digital Comparator output at time=0
NUMBITS Number of Bits Integer   none Number of input bits to the Digital Comparator
OUT_DELAY Propagation Delay Number 1f to 1024 s Delay from when the input state changes until the output changes
RIN Input Resistance Number min: 100 Ω Input resistance of each Digital Comparator input pin
ROUT Output Resistance Number min: 1m Ω Output resistance of each Digital Comparator output pin
VOH Output High Voltage Number any V Output high voltage for each Digital Comparator output pin
VOL Output Low Voltage Number any V Output low voltage for each Digital Comparator output pin