Legend Design Technology announces MSIM, a circuit simulator for layout-based characterization

SUNNYVALE, CALIFORNIA --May 31, 2002-- Legend Design Technology is proud to announce the release of their latest product, MSIM a high performance characterization-oriented circuit simulator. Together with their other tools (SpiceCut (automatic critical-path circuit building tool) and MemChar (automatic memory characterization tool)), MSIM completes the flow providing industry's first comprehensive and automated solution to the tedious and error prone processes associated with the characterization, validation, and verification of SoC embedded memory.

Legend Design Technology's unique layout-based characterization flow generates optimized timing and power models for use in system simulation that reflect the reality of the silicon. Accuracy in characterization can make the difference between a successful silicon spin (high yield) or a failed one (low yield, time and cost of a re-spin). With the increasing cost of a tape-out (.1 micron process approximately 2 million dollars) and a shrinking time to market window, companies today can not tolerate a failed tape-out.

In order to generate accurate timing and power models, characterization through numerous circuit simulations with the appropriate Spice models are required. The complete flow (SpiceCut, MemChar, MSIM) automates volumes of simulations by supporting parallel computing for high throughput. Through automation, integration, and concurrent simulation, companies can maximize engineering time and minimize the uncertainty associated with SoC design.

Legend's Integrated Solution for Characterization and Simulation
SpiceCut is a critical-path circuit builder and MemChar an automatic memory model generator. To speed runtime for hundreds of simulations, SpiceCut automatically builds critical-path circuits from the extracted layout. MemChar takes in the critical path netlists, Spice Model, and data sheet specifications to automatically generate the simulation stimulus and controls, (ie. set-up/hold time and minimum clock width). MemChar's simulation manager then calls MSIM for running volume simulations and measurements. Lastly, MemChar uses the data obtained from MSIM to build the timing and power models (.LIB or .TLF). MemChar automates all processes in the flow, including simulations and optimizations.

Quality Characterization for Preventing Glitch and Timing Soft Error
Critical timing in high performance designs is forcing engineers to move from a schematic-based characterization flow to a more realistic physical view which takes into account parasitics, coupling, and distributed effects. Layout parasitic extraction is the driving force behind the Legend Design Technology flow. This point is best illustrated in the bisection model of a memory instance.

Traditional memory timing is characterized by a path difference. Path difference will show a hard error viewable at the output pins, but falls short of detecting racing conditions and glitches inside the latches. 'Timing Soft Error' is the term associated with this extremely difficult to see and often overlooked timing behavior.

MemChar's bisection model is built by a patented binary optimization algorithm that determines the true set-up and hold times, effectively removing the risk of failure associated with Timing Soft Error. It should be noted that MemChar can automatically set up both Path Mode (fast) and Bisection (high accuracy) characterization conditions.

Automatic Critical-Path Circuits Building from Layout
It comes as no surprise to anybody with experience characterizing embedded memory that the biggest bottleneck in the flow is building the critical path circuits. This daunting task is extremely error prone and time consuming and is becoming more challenging as technology evolves. SpiceCut solves this problem by automatically building the critical path circuits from the extracted layout and/or schematic. The tool recognizes all nodes and latches, and takes into account all the paths. Its built in RC reduction will produce equivalent circuits that speed up simulations considerably. For large memory instances (>500K) layout extraction could take an extremely long time, but SpiceCut is able to function on a ring-shape extraction providing greater than a 10X speed improvement.

MSIM: Circuit Simulator for Characterization
SpiceCut and MemChar will set the stage for memory characterization, but it is up to the circuit simulator to get the results (timing, power). MSIM is Legend Design Technology's latest product and is a true characterization oriented circuit simulator. Its feature set and pricing model position the product perfectly for memory characterization, but it is equally ideal for the characterization of standard cell libraries.

MSIM combines a matrix-inversion based circuit simulator with RC reduction to deliver unparalleled accuracy, performance and value. Proprietary RC reduction technology enhances performance by reducing the size of the circuit matrix due to RC's, thus improving convergence by transforming simulation conditions from 'ill' to 'well'. MSIM supports all BSIM models from major foundries.

Benchmark results of MSIM with RC reduction on SRAM access time is shown below

 Standard*MSIMComparison
Accuracy3.41 ns3.39 ns0.59%
CPU Time3,867 sec317 sec12.2 X

* Standard means the most popular Spice simulator.

Parallel Processing for Performance
Technology is moving rapidly from 0.18um, 0.15um, 0.13um and 0.10um. Along the way, the timing and power models of memory become increasingly complex. For example, access time table of input slopes versus output loadings is in the size of 3 by 3 for 0.18 um technology, but 7 by 7 for 0.13um technology. Furthermore, each process variant such as typical, slow and fast must have its own characterization. As such, the need for volume simulations in memory characterization has become indispensable.

To provide high throughput, multiple MSIM jobs can be run concurrently in characterization system. For example, to generate a 5 by 5 table of access time, there are 25 MSIM simulation jobs required. The benchmark results below show variations on concurrency on a register file.

 CPU TimeGains
1 MSIM7 Hours 17 Minutes1.0 X
4 MSIM2 Hours 8 Minutes3.4 X
8 MSIM1 Hour 13 Minutes6.0 X
25 MSIM18 Minutes23.9 X

Conclusion
Legend Design Technology is the first company to provide a complete embedded memory characterization flow based on layout extraction. The success enabling capability of the tools will be realized in engineering productivity gain, successful SoC fabrication, and achieving time-to-market targets.

MemChar, SpiceCut and MSIM are commercially available on Sun Solaris, HP-UX and Linux platforms. Legend also provides characterization services for memory validation and model fine-tuning.

About Legend Design Technology, Inc.

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