Transistor level verilog

The present invention relates to an apparatus and method for describing transistors within the leaf cell and the interconnection between the transistors.

Electronic components are becoming increasingly complex as more and more capability is being designed into the electronic components. Typically, the more complex an electrical component becomes, the greater number of semiconductor devices that need to be used to form the circuits that carry out the functions.

In the past, circuits are designed using a graphical tool to draw schematic diagrams of the circuits. Designers use a graphical program, such as Composer which is available from Cadence, Inc. of San Jose, Calif. Drawing the schematic is actually a graphical process in which the designer uses symbols to designate one of various types of transistors, such as for an NMOS or PMOS transistor. A number of transistors are designated with the transistor type, and then a wiring feature is used to connect terminals of all the designated devices together. The designer provides input ports and output ports and annotates the symbols to specify certain properties for a particular transistor. The properties specified include length and width of a gate of a transistor. Other size properties may also be designated. In short, past efforts for circuit design include a graphical way of trying to describe the particular components and the way the components are connected. Another trend is to design at least some portions of a circuit from certain building blocks (called leaf cells) which include a group of transistors. Rather than design a circuit totally from scratch, the circuit is designed by connecting these building blocks or leaf cells.

Before actually building the circuit, several tests are performed on the circuit as designed. The first test is a functional simulation. The functional simulation attempts to assure that the design of the circuit is correct. In other words, for a certain set of inputs, the circuit should produce a certain set of outputs in order for the circuit to be correctly carrying out a function. A first series of scripts or procedures are applied to the graphical data used to design the circuit. The series of scripts or procedures converts the graphical data to a hardware description language (“HDL”). One commonly used HDL is known as Verilog. Once the HDL is formed a simulation program, such as VCS Simulator available from Synopsis of Mountain View, Calif. is used to test the functionality of the circuit. Verilog is a HDL that is used to interconnect the blocks for the purpose of running a functional simulation test.

In addition, another simulation test is used to check other aspects of the circuit. A Simulation Program Integrated Circuits Especially! (“SPICE”) test is also generally performed on a circuit. The SPICE test is used to provide a reasonably detailed analysis of circuits containing active components such as bipolar transistors, field effect transistors, diodes and lumped components such as resistors, capacitors and inductors. SPICE is a circuit simulation program rather than a logic simulation program. Thus SPICE considers the voltages and currents in a circuit to be continuous quantities, not quantized into high/low values. SPICE can be used for many purposes, one of which is to simulate the timing of signals passing through the circuit. SPICE is used to identify certain problems with the design before the actual design is fabricated. Identified problems can be rectified before actually manufacturing the circuit. A second series of scripts or procedures are applied to the graphical data to convert the SPICE format. The SPICE simulation is then run on the converted graphical data.

In short, current circuit design includes using a graphical tool to draw schematic diagrams of the circuits. The circuit designer uses symbols to designate one of various types of transistors, such as for an NMOS or PMOS transistor. The resulting graphical data and designations are then converted into Verilog for a first test. The graphical data and designations are also converted into SPICE format for use in the SPICE simulation.

This method of circuit design has several problems. Among the problems is that the conversion programs are not always perfect. For example, when the conversion program converts the graphical data and designations into a hardware description language, such as Verilog, problems can occur in the functional simulation of the logic. Generally, the functional simulation of the logic results in the logic checking out correctly when in fact there is a mistake in the logic. The same can happen in the SPICE simulation. In other words, the SPICE simulation can result in the circuit checking out correctly when in fact there may be a flaw that needs to be corrected. Yet another problem is that some designers prefer not to design a circuit using graphical data and designations.

Therefore, there is a need for syntax which will avoid the necessity of converting from graphical data and designations of the transistors to a hardware description language, such as Verilog. There is still a further need to allow the design of circuits without using graphical data and designations of on the transistors.

Method includes specifying a first set of interconnected devices associated with a first leaf cell in Verilog syntax, and specifying a second set of interconnected devices associated with a second leaf cell in Verilog syntax. A connection between the first leaf cell and the second leaf cell is also specified in Verilog syntax. This specifies a circuit. The functionality of the logic can be tested by running a logic simulation on the circuit without converting to Verilog syntax. The Verilog syntax, associated with the circuit, can be converted directly from Verilog syntax to a SPICE netlist. The SPICE netlist can be used to simulate the timing and other parameters of the circuit. The Verilog syntax can be used to verify that the circuit as built. Specifying the first set of interconnected devices associated with the first leaf cell further includes specifying parameters needed for the SPICE netlist as a comment in the Verilog syntax. In addition, specifying the second set of interconnected devices associated with the second leaf cell also includes specifying parameters needed for the SPICE netlist as a comment in the Verilog syntax.

A computer readable medium includes an instruction set for causing a suitably programmed computer system to execute the method set forth in the previous paragraph. In addition, a data structure includes a first portion which controls portion of the Verilog simulation and is ignored by the SPICE simulation, and includes a second portion which controls the SPICE, simulation and is ignored by the Verilog simulation.

A method includes inputting a plurality of commands having a syntax language wherein each command includes a first specification and a second specification. The method also includes executing a logic simulation controlled by the first specification and ignoring the second specification in the logic simulation. The method also includes executing a timing simulation controlled by the second specification and ignoring the first specification in the timing simulation. In some embodiments, executing a logic simulation controlled by a first simulation and ignoring the second specification includes designating the second specification as a comment field to the logic simulation. Executing a timing simulation controlled by the second specification and ignoring the second specification includes designating the first specification as a comment field to the timing simulation. Executing the logic simulation further comprises executing a file using a hardware description language. In some embodiments, the hardware description language for executing the logic simulation is Verilog. In some embodiments, the timing simulation is executed using a file in SPICE format. In some embodiments, executing the timing simulation includes converting a file in Verilog to a file in SPICE format. More generally, executing the timing simulation further includes converting the logic simulation file format to a timing simulation file format.

An article of manufacture includes a computer readable media having instructions thereon. The instructions cause a suitably programmed system to execute a method that includes inputting a plurality of commands having a syntax language wherein each command includes a first specification and a second specification. The method also includes executing a logic simulation controlled by the first specification and ignoring the second specification in the logic simulation. The method also includes executing a timing simulation controlled by the second specification and ignoring the first specification in the timing simulation.

A data structure includes a plurality of command records each following a language syntax wherein each one of the plurality of command records includes a first specification and a second specification. The first specification provides information to be executed by a logic simulator and ignored by a timing simulator. The second specification provides information to be executed by a timing simulator and ignored by a logic simulator.

An article of manufacture includes a computer readable media having a data structure for causing a suitably programmed system to execute a logic simulation that is controlled by the first specification and a timing simulation that is controlled by the second specification. The data structure of the article of manufacture includes a plurality of command records each following a language syntax wherein each one of the plurality of command records includes a first specification and a second specification. The first specification provides information to be executed by a logic simulator and ignored by a timing simulator. The second specification provides information to be executed by a timing simulator and ignored by a logic simulator. In some embodiments, the article of manufacture the data structure causes a suitably programmed system to execute a Verilog simulation that is controlled by the first specification and a SPICE simulation that is controlled by the second specification.

A simulation system includes storage that holds a plurality of commands having a syntax language wherein each command includes a first specification and a second specification. The simulation system also includes a logic simulator that is controlled by the first specification and that ignores the second specification. The simulation system also includes a timing simulator that is controlled by the second specification and that ignores the first specification. In some embodiments of the simulation system, the plurality of commands are written in Verilog. In some embodiments, the timing simulation includes a set of instructions for converting Verilog directly into a SPICE netlist. The set of instructions for converting Verilog directly into a SPICE netlist includes a set of instructions for reading the second specification which includes parameters needed to produce the SPICE netlist. The first specification is designated as being located in least one comment field by the set of instructions for converting Verilog directly into a SPICE netlist. The second specification is placed in at least one comment field in the Verilog.

An article of manufacture includes a computer readable media having plurality of command records stored thereon. Each command record has a logic-simulation specification and a timing-simulation specification for causing a simulation system to execute a logic simulation that is controlled by the logic-simulation specification and a timing simulation that is controlled by the timing-simulation specification.

The invention is pointed out with particularity in the appended claims. However, a more complete understanding of the present invention may be derived by referring to the detailed description when considered in connection with the figures wherein like reference numbers refer to similar items throughout the figures and:

FIG. 1 a flow chart of the operations of a the simulation system of the present invention.

FIG. 2 is a schematic diagram of a NAND gate leaf cell.

FIG. 3 is a text listing in a Hardware Description Language specifying the NAND gate leaf cell of FIG. 2 .

FIG. 4 is a flow chart of the conversion of a set of commands placed in a Hardware Description Language into another format for a second simulation.

FIG. 5 shows a data set which is converted from the Hardware Description Language into a SPICE netlist for a second simulation.

FIG. 6 is a SPICE netlist which results from conversion of a set of commands placed in Hardware Description Language using the conversion program described in the “MAN” page.

FIG. 7 is a block diagram of the electronic device simulation system consistent with the present invention.

The description set out herein illustrates the various embodiments of the invention and such description is not intended to be construed as limiting in any manner.

In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings which form a part hereof, and in which are shown by way of illustration specific embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention.

FIG. 1 is a flow chart of the operation 100 of a simulation system 700 (shown in FIG. 7 ) of the present invention. The overall operation of the simulation system 700 includes initially specifying a plurality of interconnected devices in a Hardware Description Language, as depicted by reference numeral 110 . The Hardware Description Language used in one preferred embodiment is Verilog. The plurality of interconnected devices includes leaf cells. Leaf cells are a collection of transistors that represent a low-level function, such as a NAND gate, an AND gate, a MUX, and other, similar low-level functions. A syntax is developed in Verilog, which is able to describe the function of the leaf cell, and also uniquely describe the transistor connections within the leaf cell. In addition, Verilog also describes the connection between the plurality of leaf cells. When designing a circuit, various leaf cells having various functions can be interconnected. The Verilog syntax developed describes the function of the leaf cell, as well as the transistor usage and connections within the leaf cell and among the various leaf cells formed in the circuit. The initial step includes using a Verilog syntax that includes assigned statements, and extra comments within the syntax that can be used to infer the type of transistors, NMOS or PMOS. The details of specifying the various interconnected devices in the Hardware Description Language called Verilog will be discussed with respect to FIGS. 2 and 3 below.

The next step is to simulate the functionality of logic of the interconnected devices, using the Hardware Description Language as written, as depicted by reference numeral 112 . The Verilog syntax developed is used to directly simulate the logic of the interconnected devices within the leaf cells, as well as between the leaf cells. The Hardware Description Language, as written, is converted into another format. The Verilog, which describes the interconnections between the transistors within leaf cells is then converted to transistor-level SPICE. SPICE stands for Simulation Program Integrated Circuits Especially, and is used to provide a detailed analysis of circuits containing active components, such as bipolar transistors, field effect transistors, diodes, and lump components such as resistors, capacitors, and inductors. SPICE is a circuit simulation program, and is not a logic simulation program, and therefore it is a different simulation from the simulation also run for functional logic, which uses the Verilog syntax as written. Conversion of the Hardware Description Language, or Verilog, as written to the SPICE format results in a SPICE netlist, that can be used to simulate the other parameters of the interconnected devices, as depicted by reference numeral 116 in FIG. 1 .

FIG. 2 is a schematic diagram of a NAND gate leaf cell 200 . The NAND gate leaf cell 200 includes an input A 210 and an input B 212 , and also includes an output Z 220 . The NAND gate 200 includes an NMOS transistor M 1 , an NMOS transistor M 2 , a PMOS transistor M 3 , and a PMOS transistor M 4 . The NMOS transistors M 1 , M 2 have a source, a gate, and a drain. The drains of the Ml and M 2 NMOS transistors are attached to ground 230 . The source of the transistors M 3 and M 4 is attached to VDD 240 . The NAND gate 200 is a logic unit or circuit that only does not produce an output when there is both an input from A and an input from B.

FIG. 3 is a text listing in a Hardware Description Language specifying the NAND gate leaf cell 200 of FIG. 2 . The Hardware Description Language shown in FIG. 3 is Verilog. The hardware description language starts with a Verilog module statement 310 . In the Verilog module statement there is a name of the leaf cell, followed by a parentheses, in which the ports z, a, and b are listed. In the next line, 312 , the output port is defined as port Z. The next line, 314 , defines the input ports as A and B. The next line, 316 , is a wire statement, which shows the connectivity beyond the primary ports A, B, and Z. The wire statement defines the structure as int_Z. The next statement, 318 , is an assign statement, which assigns the meaning to int_Z. The assign statement 318 describes the transistor (M 1 , M 2 , M 3 , M 4 ) interconnects between the ports A, B, and Z, and the ground 230 , and VDD 240 . The assign statement describes the connection to the Z output, which, as shown in FIG. 2 , is between ground 230 and VDD 220 . Int_Z equals 1′b0 and A and B, or, as denoted by the vertical pipe, 1′b1 and the complement of A, and 1′b0 and the complement of B. 1′b0 indicates the low state, which is the ground connection 230 . Zero is the low state, which is equal to the ground 230 . So 1′b1 really shows a source connection onto M 1 in the schematic shown in FIG. 2 . The &˜A means A is connected to the gate. The continuing function is that A and B create a temporary node, which is not defined, between the transistors M 1 and M 2 , and connects the source and drains together. B, the first line of the assign statement, connects the gate to the B input 212 . Therefore, the first line shows the path from the int_Z through the M 2 transistor through the temporary node down through the M 1 transistor down to the ground connection 230 . The portion of the line begins with a vertical pipe, which is the same as an OR, which in turn implies that there is another connection to the int_Z net. The OR statement also implies that it's going to have two connections. One is a 1′b1 and not A, refers to the M 3 PMOS transistor. The 1′b1 indicates a high signal (VDD 220 ) connected to the source of the M 3 transistor. The &˜A indicates a PMOS device, and A means the A net is fed directly into M 3 . Continuing on with the second line of the assign statement, the vertical pipe denotes an OR, so it denotes that the int_Z net has yet another connection. The connection is 1′b1 AND˜B. This last portion of the statement refers to the PMOS transistor, labeled M 4 in FIG. 2 . And the 1′b1 indicates that the source is connected to high signal VDD. ˜B means that it's PMOS, and that the B terminal connects to the gate. Using ampersand for an AND function, a vertical pipe for an OR function, and using a˜for meaning the complement, each of the transistors of the leaf cell and the logic associated therewith can be denoted using Verilog language.

The next line is a tlv statement. The tlv statement carries a reference numeral 320 . In front of the tlv statement are two forward slashes, which indicates to Verilog that this is a comment. The first tlv statement includes the letters abs int_Z. This tlv statement, or comment, 320 , is an ordered list of the device sizes that are connected in the terminal int_Z. The order is set up to follow the definition set up in the assign statement 318 . The first two go to the size of the connections to the A gate and B gate for the NMOS devices M 1 and M 2 . The tlv statement, or comment, indicates that the A gate and B gate are each 5 microns and 5 microns, respectively. The next line also has two forward slashes, and is part of the tlv abs int_Z comment or statement. The next line of this particular comment 320 defines the size of the PMOS devices M 3 and M 4 , as connected to the A and the B gates. Of course, any size can be placed in this ordered set. It should be noted that even fractional sizes may be used to denote the size of the devices in the tlv comment line 320 . The actual size is critical to the second simulation. The absolute sizes are actually the width of the various gates for the various transistors M 1 , M 2 , M 3 , and M 4 . Next is an assign statement 322 , which defines the actual output Z=int_Z. The next statement is another comment, tlv output Z, which carries the reference numeral 324 . This particular comment is basically a shorthand notation to allow either an inverter or set of inverters to be built to give a certain output drive strength. The 6 is actually a ratio between P and an attached end device. Generally it's useful to have really high drive strength output, and through ratioed output, a series of inverters can be generated that drive up to that maximum output. In short, what's shown here in FIG. 3 is a simple example that shows that the basic logic function can be displayed or specified using an assign statement that instantiates the NMOS and PMOS devices, and then a syntax can be used to generate inverters to drive the output.

The inverter is just a stacked set of NMOS and PMOS devices which are connected. The default ratio is set between the NMOS and PMOS devices of the inverter. The statement basically defines the N-channel side, and then a default ratio calculates what the PMOS size is for the inverter. The output is assigned Z, and then the input to the inverter is int_Z. Therefore, the last statement shows how to build an output driver, or inverter that is used as an output driver.

The Hardware Description Language, or Verilog, shown in FIG. 3 can then be used with a Verilog simulator, such as VCS available from Synopsis of Mountainview, Calif. The Verilog simulator reads the Verilog language as written in FIG. 3 . It should be noted that the comment fields, such as 320 and 324 , are not read by the VCS simulator, and therefore these are disregarded for terms of running the Verilog simulation. Therefor, the Verilog simulator, such as VCS, is used to perform a simulation of the functional logic of the leaf cell, of the example NAND gate shown in FIG. 2 and specified in FIG. 3 . It should be noted that each leaf cell can be similarly defined, and then the leaf cells can also be interconnected to produce a Verilog language which describes the internal connections of each leaf cell and the interconnection among leaf cells. This, too, can be input to the Verilog simulator, such as VCS, to do a logical function simulation on the circuit formed.

The Verilog language as written in FIG. 3 can be converted from the HardwareDescription Language such as Verilog into another format for a second simulation. FIG. 4 shows the method. Initially, the circuit is described in transistor level Verilog, which includes comment fields containing comment information necessary for the second simulation, as depicted by reference numeral 412 . The result of the conversion program is applied to the transistor level Verilog specification, such as the one shown in FIG. 3 , as depicted by reference numeral 412 . The result of the conversion is a SPICE netlist, which is used to run a second simulation, as depicted by reference numeral 414 . The conversion program includes extracting information from the comment fields of the Verilog specification 320 , 324 of FIG. 3 , and using these to produce a file necessary to run the second simulation. In this particular embodiment of the invention, the second simulation is a SPICE simulation, which performs detailed analysis of circuits containing active components, such as bipolar transistors, field-effect transistors, diodes, and lump component such as resistors, capacitors, and inductors. SPICE considers the voltages and currents in a circuit to be a continuous quantities not quantatized into high and low values.

FIG. 5 depicts a data set for data structure 500 , which includes optional header information 510 and optional footer information 530 . Between the header 510 and the footer 530 are a number of records of data 520 , 522 , 524 , 521 , 523 and 525 . In actuality, there can be N records of data, as depicted by the three dots between data records 522 and 524 . Each record includes a Verilog specification 520 and a SPICE specification 521 . In other words, the data structure sets forth or specifies data necessary to run a Verilog simulation, such as records, which would be found in portions of the records 520 , 522 and 524 , and portions which are necessary to run a second simulation, or SPICE simulation. In other words, the records also include a SPICE specification portion 521 , 523 , 525 . For the purposes of running a simulation which requires Verilog, the SPICE specification portions 521 , 523 , 525 are ignored. When running a second simulation, the Verilog portions 520 , 522 , 524 of the records are ignored. The second simulation may or may not require that the data structure 500 be converted. As described herein, the second simulation requires conversion of the text listing of the Hardware Description Language shown in FIG. 2 into a SPICE netlist. However, it is contemplated that a second simulation could be run on data which includes portions which are to be ignored by a program running the second simulation.

Shown below is a manual page that shows the translation of the transistor level Verilog, such as shown in FIG. 3 , to a SPICE format or SPICE netlist. The details of this manual page are set forth in Table 1 below.

FIG. 6 is a SPICE netlist which results from conversion of a set of commands placed in Hardware Description Language using the conversion program described in the “MAN” page. The SPICE netlist is used to perform the SPICE simulation. The SPICE simulation provides a detailed analysis of the circuits containing active components, as mentioned previously.

FIG. 7 is a block diagram of the electronic device simulation system consistent with the present invention. A computer simulation system 700 is shown in FIG. 7 . Systems consistent with the present invention may be implemented using a conventional personal computer, such as an IBM compatible personal computer. FIG. 7 shows the computer system 700 and the architecture 705 of one such computer 700 for executing a first simulation program and a second simulation program as part of a simulation system. As shown, architecture 705 uses system bus 740 to connect RAM 710 , ROM 720 , CPU 730 , storage device 750 , monitor 760 , keyboard 770 , and mouse 780 . These are all standard components of a personal computer. For example, CPU 730 may be a microprocessor manufactured by Intel Corp. or manufactured by Advanced Micro Devices or the like. Likewise, the other components are generally standard on most personal computers or workstations, with one exception, the storage device 750 . The storage device 750 includes three components. The components include transistor size and ratio, database 752 , first simulation program (Verilog/VCS) 754 , and a second simulation program such as a SPICE simulation.

Database 752 includes a variety of information, including rules related to the size of the transistor device for a given placement in a comment field such as 318 , and for the given placement within the comment field. The rules of database 352 are typically criteria used in determining size for the second simulation. Database 352 also includes information on, for example, the default values and ratios needed for building inverters for a given leaf cell, such as shown and specified in FIGS. 2 and 3 .

Advantageously, the transistor level verilog specification such as shown in FIG. 3 can be run directly without conversion to perform a functional logic test. Yet another advantage is that circuits can be designed without the need to use graphical data or a graphics package. The circuit design can be done using a text design tool. A further advantage of this is that the formed circuit can be stored as text rather than as graphical data. The textual data requires less storage than corresponding graphical data necessary to fully describe the circuit. Still a further advantage is that the text data of the circuit can be used to verify the circuit after it has been manufactured or built.

Conclusion

In conclusion, a method includes inputting a plurality of command having a syntax language wherein each command includes a first specification and a second specification. The method also includes execution a logic simulation controlled by the first specification and ignoring the second specification in the logic simulation. The method also includes executing a timing simulation controlled by the second specification and ignoring the first specification in the timing simulation. In some embodiments, executing a logic simulation controlled by a first simulation and ignoring the second specification includes designating the second specification as a comment field to the logic simulation. Executing a timing simulation controlled by the second specification and ignoring the second specification includes designating the first specification as a comment field to the timing simulation. Executing the logic simulation further comprises executing a file using a hardware description language. In some embodiments, the hardware description language for executing the logic simulation is Verilog. In some embodiments, the timing simulation is executed using a file in SPICE format. In some embodiments, executing the timing simulation includes converting a file in Verilog to a file in SPICE format. More generally, executing the timing simulation further includes converting the logic simulation file format to a timing simulation file format.

An article of manufacture includes a computer readable media having instructions thereon. The instructions cause a suitably programmed system to execute a method that includes inputting a plurality of commands having a syntax language wherein each command includes a first specification and a second specification. The method also includes executing a logic simulation controlled by the first specification and ignoring the second specification in the logic simulation. The method also includes executing a timing simulation controlled by the second specification and ignoring the first specification in the timing simulation.

A data structure includes a plurality of command records each following a language syntax wherein each one of the plurality of command records includes a first specification and a second specification. The first specification provides information to be executed by a logic simulator and ignored by a timing simulator. The second specification provides information to be executed by a timing simulator and ignored by a logic simulator.

An article of manufacture includes a computer readable media having a data structure for causing a suitably programmed system to execute a logic simulation that is controlled by the first specification and a timing simulation that is controlled by the second specification. The data structure of the article of manufacture includes a plurality of command records each following a language syntax wherein each one of the plurality of command records includes a first specification and a second specification. The first specification provides information to be executed by a logic simulator and ignored by a timing simulator. The second specification provides information to be executed by a timing simulator and ignored by a logic simulator. In some embodiments,, the article of manufacture the data structure causes a suitably programmed system to execute a Verilog simulation that is controlled by the first specification and a SPICE simulation that is controlled by the second specification.

A simulation system includes storage that holds a plurality of commands having a syntax language wherein each command includes a first specification and a second specification. The simulation system also includes a logic simulator that is controlled by the first specification and that ignores the second specification. The simulation system also includes a timing simulator that is controlled by the second specification and that ignores the first specification. In some embodiments of the simulation system, the plurality of commands are written in Verilog. In some embodiments, the timing simulation includes a set of instructions for converting Verilog directly into a SPICE netlist. The set of instructions for converting Verilog directly into a SPICE netlist includes a set of instructions for reading the second specification which includes parameters needed to produce the SPICE netlist. The first specification is designated as being located in least one comment field by the set of instructions for converting Verilog directly into a SPICE netlist. The second specification is placed in at least one comment field in the Verilog.

An article of manufacture includes a computer readable media having plurality of command records stored thereon. Each command record has a logic-simulation specification and a timing-simulation specification for causing a simulation system to execute a logic simulation that is controlled by the logic-simulation specification and a timing simulation that is controlled by the timing-simulation specification.

A simulation system includes storage that holds a plurality of command records having a syntax language wherein each command record includes a first specification and a second specification. The simulation system includes logic simulation apparatus that is controlled by the first specification and that ignores the second specification. The simulation system also includes a timing simulation apparatus that is controlled by the second specification and that ignores the first specification.

A method includes specifying a first set of interconnected devices associated with a first leaf cell in Verilog syntax, and specifying a second set of interconnected devices associated with a second leaf cell in Verlilog syntax. A connection between the first leaf cell and the second leaf cell is also specified in Verilog syntax. This specifies a circuit. The functionality of the logic can be tested by running a logic simulation on the circuit without converting to Verilog syntax. The Verilog syntax, associated with the circuit, can be converted directly from Verilog syntax to a SPICE netlist. The SPICE netlist can be used to simulate the timing and other parameters of the circuit. The Verilog syntax can be used to verify that the circuit as built. Specifying the first set of interconnected devices associated with the first leaf cell further includes specifying parameters needed for the SPICE netlist as a comment in the Verilog syntax. In addition, specifying the second set of interconnected devices associated with the second leaf cell also includes specifying parameters needed for the SPICE netlist as a comment in the Verilog syntax.

A computer readable medium includes an instruction set for causing a suitably programmed computer system to execute the method set forth in the previous paragraph. In addition, a data structure includes a first portion which controls portion of the Verilog simulation and is ignored by the SPICE simulation, and includes a second portion which controls the SPICE simulation and is ignored by the Verilog simulation.

The foregoing description of the specific embodiments reveals the general nature of the invention sufficiently that others can, by applying current knowledge, readily modify and/or adapt it for various applications without departing from the generic concept, and therefore such adaptations and modifications are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments.

It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Accordingly, the invention is intended to embrace all such alternatives, modifications, equivalents and variations as fall within the spirit and broad scope of the appended claims.