Introduction

The latest release of Layout versus Schematic tools from CELEBRITY CAD suite (Maverick full-chip parametric netlist extractor and Guardian hierarchical netlist comparator) delivers a number of significant advances. The engines of both tools were tuned up to achieve essential reduction of running time while processing huge designs. Maverick and Guardian became integrated more with other CELEBRITY systems. They provide extended setups that are easily customized, and offer new functions that serve to achieve better precision for parameter extraction. Maverick and Guardian reduce the number of verification/ modification iterations.

LVS Cross-View Navigator

LVS Cross-View Navigator provides easy and convenient way to analyze the results of the LVS run and to make necessary corrections in the design. Using this tool (Figure 1) makes it possible to view all nodes mentioned in reports directly on layout and schematic graphical views from the perspective of both netlists (extracted from layout and derived from schematic) involved in comparison.

Figure 1. Workbench of LVS Navigator.

Utilizing the capabilities of Silvaco Intertool Communication Server (Figure 2), LVS Navigator provides drive among basic LVS results, points out the relevant node names on target report and netlists (Figure 3) and highlights images of devices (Figure 4) or nets (Figure 5) simultaneously in Expert Layout Processor and Scholar Schematic Capture.

Figure 2. Reference Panel of Inter-Tool
Communication Server.

Figure 3. Combined View of Compared
Netlists and Active LVS Report

Figure 4. Device Cross-View
initiated by LVS Navigator

Figure5. Highlighting of nets in
Expert and Scholar drawings.

SHOW SCOPE: The user of Cross-View Navigator is offered with the possibility to trace any subset or full scope of the related views:

Post-run LVS report from one of the predefined categories (see below)

SPICE Netlist extracted from layout cell

SPICE Netlist produced by schematic capture

Layout presented in the active window of Expert layout processor

Schematic drawing loaded in Scholar schematic capture graphical window

The flexible scope gives the user the convenience of having a small number of views necessary for the particular verification activity on the screen.

NODE TYPE: As long as all basic LVS reports (matches, discrepancies, etc.) are split between relations involving nets and devices, LVS navigator works in one of the two corresponding modes - to show nets or instances (devices) inside all views included into the show scope.

REPORT CATEGORY: The set of design elements to be browsed during particular navigation session is defined by the nature of the report under consideration. LVS Cross-View Navigator supports (Figure 6) four categories of reports for browsing control:

Matched Nodes (based on LVS report which is contained in .MTC file)

Unmatched Nodes (based on .UNM file)

Discrepancies (based on .UNM file)

Parameter Errors (based on .PAR file)

Figure 6. Choice of Report Categories
in LVS Cross-View Navigator

Note the difference between discrepancies and unmatched nodes. Both of them reference nets and instances (devices) that had not been matched by Guardian. For discrepancies, potential matches are generated by the tool (in most cases it means that if some local errors were fixed, these nodes would match), while for unmatched nodes they are not produced. For example, if one of the netlists contains some extra device which cannot be merged with other ones and has no equivalent in another netlist, the mentioned device should be classified as an unmatched node.

ACTIVE NETLIST / BROWSE STRATEGY: These settings affect the order of LVS report processing in the case of hierarchical netlists. ACTIVE NETLIST determines the netlist whose hierarchy will be taken into account while applying the selected strategy. STRATEGY, in turn, can be Top-Down or Down-up. The first choice means that references from the active netlist that are taken from the root (top) subcircuit are processed first, then the references are taken from primary instances from the root, and so on down to the leaf subcircuits (which do not contain instances of the other subcircuits).

SUBCIRCUIT: The choice of a subcircuit from the active netlist is provided to reduce navigation to those nodes that are contained in this subcircuit.

NAVIGATION COMMANDS: The "Start" command serves to activate the browsing list after changing any options (category, strategy etc.). The "Next" and "Previous" commands provide the initiation (highlighting) of nodes which are mentioned in the browsing list after or before the currently processed ones.

Extended Specifications for Resistor Parameters in Maverick

Maverick extracts geometry-dependent resistance value for resistors. The efficient numerical procedure implemented in Maverick provides high accuracy of extracted resistance values for resistors of arbitrary configuration. Theoretically, those values like head and contact resistance traditionally prescribed to some resistors are not needed, because the head shape is taken into account automatically. For contacts a separate type of resistor could be defined. However, to meet common approaches, some extensions in definition of resistors were made (Figure 7). This provides more flexibility in definition of device recognition layers for various types of resistors.

Figure 7. Extended resistor setup.

To extract the value of the resistance, the user has to specify non-zero value for at least sheet resistance. Contact resistance is treated as the resistance of a single contact shape. If actual connection of a resistor head has been designed using a group of contact shapes, resistances of all of those shapes are summed as usual parallel resistors.

If resistor heads are parts of resistor recognition layers (see, for instance, grey area in Figure 8), then the head resistance is calculated from geometrical information and sheet resistance value is specified. The value of head resistance shown in Figure 7 is ignored in this case. If the resistor recognition shape (see the hatched area in Figure 9) does not cover the resistor head's areas, then the head resistance is not calculated. The extractor utilizes the value of head resistance shown in Figure 7 instead.

Figure 8. Resistor heads are parts of
recognition layers: automatic
calculation of head resistance.

Figure 9. Resistor heads are not in
recognition layers: head resistance
should be prescribed.

Resistance extraction routines need sheet resistance value (in Ohms/square) to be specified for the resistor recognition layer in the technology file. This can be done in the way as the following fragment of Expert technology file shows.

Layer

{

Name = "N-Act"

...

Material

{

MaterialName = ""

Resistivity = 555

Permittivity = -1.00

Thickness = 1.00

}

}

The layer N-Act is the resistor recognition layer with sheet resistance equal to 555 Ohm/square. The whole set of resistor parameters is specified using the set of the following constructions within Device statement.

DevParam

{

NameP = "XXXXXXXXX"

ValueP = 100

}

NameP can be one of the following predefined strings:

"SheetRes" for sheet resistance

"DeltaW " for width outdiffusion parameter

"DeltaL" for length outdiffusion parameter

"HeadRes" for head resistance

"ContRes" for contact resistance

ValueP indicates the actual numerical value of the parameter

Conclusion

Silvaco's verification suite (Maverick, Guardian, Savage, Dragon) is a dynamically developing system, permanently adjusting to the diversity of customer needs. The evolution of verification tools is followed by their tight integration with layout processor and schematic capture. This allows the designers to run complicated projects much faster and more accurately.