Logic Design for Array-Based Circuits

by Donnamaie E. White

Copyright © 1996, 2001, 2002 Donnamaie E. White

 

Simulation

Last Edit July 22, 2001


Simulation Rules

Each vendor will have specific rules for the simulations that are to be used to generate test vectors including: initialization, file sizes, number of output signals that can change per vector (tester probe noise limitation), fault coverage, procedures for three-state and bidirectional signals, procedures for differential signals, race restrictions for data and clock signals, and any other rules peculiar to that vendor.

A partial sample simulation output file is shown below. It is a formatted output, sampled in 100 ns steps taken one simulator time step before the next input vector. All inputs are uniform in their arrival and all vendor rules were followed. This file is part of one that represents 100% fault coverage for a simple 16:1 MUX circuit. The vectors were created following Minimal Test Sequence rules (one input changes state per data change vector).

Figure 8-1 Sample Simulation Output File, Formatted
To Be Used To Generate Test Vectors


	TIME
   	9999        	0100 0010 0101 1001 1010 0100
  	19999       	1100 0010 0101 1001 1010 0100
  	29999       	0000 0010 0101 1001 1010 0100
  	39999       	1000 0010 0101 1001 1010 0110
  	99999       	1001 0010 0101 1001 1010 0100
  	109999       	0001 0010 0111 1001 1010 0100
  	119999       	1001 0010 0111 1001 1010 0110
  	129999       	0001 0010 0101 1001 1010 0110
                                     o o o 
                                     o o o
  	939999      	1000 1010 0101 1001 1010 0100
  	949999      	0000 1010 1101 1001 1010 0100
  	959999      	1000 1010 1101 1001 1010 0110
  	969999      	0000 1010 0101 1001 1010 0110
  	979999      	1000 1010 0101 1001 1010 0100
  	989999      	0000 0010 0101 1001 1010 0100
  	999999      	1000 0010 0101 1001 1010 0110

Full File Listing - Functional, Sampled Simultation 16-Bit Register with Mux Output Sample Circuit


At-Speed Simulation For Timing Verification

An at-speed simulation is one method that may be used to verify the actual timing performance of the circuit as implemented on an array against the target specification for the circuit. It is run at the maximum worst-case conditions and at the minimum worst-case conditions. Since it is run at the specified maximum operating frequency of the circuit, this simulation is not used to generate test vectors.

The at-speed simulation run before layout using worst-case multipliers and Front-Annotation can spot potential problem areas in the circuit and to assist in defining the criteria for the layout. The Front-Annotation file makes a statistically-based estimate of the metal delay and adds the actual delay due to fan-out load and any wire-ORs present. Output nets have estimated package pin capacitance and system capacitance delays.

The at-speed simulation run after layout using the Back-Annotation file can verify the actual timing performance for the array. The Back-Annotation file provides the actual metal delays for the layout combined with the actual fan-out and wire-OR delays for internal nets and actual package pin and system capacitive load delays.

Note that the at-speed simulation outputs will be time-dependent (some results are not necessarily available within one sample step). The apparent "phase delay" of some outputs relative to others makes the evaluation of at-speed simulation results a non-trivial exercise.

Timing Verifier

Engineering workstations often have a timing verifier as well as a simulator. If the array vendor supports the verifier, timing analysis using the verifier can be substituted for At-speed simulations under the array-vendor's approval.

 

Copyright @ 2001, 2002 Donnamaie E. White, White Enterprises
For problems or questions on these pages, contact dew@Donnamaie.com

CST Webinar Series



Internet Business Systems © 2016 Internet Business Systems, Inc.
595 Millich Dr., Suite 216, Campbell, CA 95008
+1 (408)-337-6870 — Contact Us, or visit our other sites:
AECCafe - Architectural Design and Engineering TechJobsCafe - Technical Jobs and Resumes GISCafe - Geographical Information Services  MCADCafe - Mechanical Design and Engineering ShareCG - Share Computer Graphic (CG) Animation, 3D Art and 3D Models
  Privacy Policy