SPICE knowledge essential for chip design

Latest update time：2021-08-31 00:25

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Source: The content is reprinted from the public account "Core Thought" by Semiconductor Industry Observer (ID: icbank), author: Zhao Yuanchuang, thank you.

On February 20 , 2011 , the SPICE Circuit Simulation Program was awarded the IEEE Milestone plaque in recognition of its contribution to integrated circuit design.

The plaque is placed at the main entrance of the Electrical Engineering Building ( Cory Hall ) at the University of California, Berkeley , because all three versions of SPICE were developed in Cory Hall . The inscription on the plaque reads:

SPICE ( Simulation Program with Integrated Circuit Emphasis ) was created as a class project at the University of California, Berkeley in 1969-1970. It evolved into the world-wide standard integrated circuit simulator. SPICE has been used to train students in the complexities of circuit simulation. SPICE and its derivatives have become an essential tool used by almost all integrated circuit designers.

SPICE (Simulation Program with Integrated Circuit Emphasis) was created at UC Berkeley as a class project in 1969-1970. It evolved to become the worldwide standard integrated circuit simulator. SPICE has been used to train many students in the intricacies of circuit simulation. SPICE and its descendants have become essential tools employed by virtually all integrated circuit designers.

The Birth of SPICE

SPICE is the abbreviation of Simulation Program with Integrated Circuits Emphasis . It was developed by the Department of Electrical Engineering and Computer Science of the University of California, Berkeley ( UC Berkeley ), with Ronald A. Rohrer and Laurence Nagel as the backbone . It was originally a simulation software designed using the FORTRAN language. It is used to quickly and reliably verify the circuit design in integrated circuits and predict the performance of circuits. It is a powerful general-purpose circuit-level analog simulator, mainly used for circuit analysis of integrated circuits. The SPICE netlist format has become the standard for common analog circuits and transistor-level circuit descriptions.

In 1970, Ronald A. Rohrer had just returned from Fairchild Semiconductor to the University of California, Berkeley, as a professor in the Department of Electrical Engineering and Computer Science.

Since he had just returned to school, Professor Ronald A. Rohrer did not have time to prepare teaching materials for the "Circuit Synthesis" course for seven graduate students. So, in the first class, he announced: students should write a circuit simulation program together.

Ronald A. Rohrer reached an agreement with Professor Donald O. Peterson , the department's director of academic affairs : as long as Professor Peterson approved the simulation programs written by the students, they would all pass. Otherwise, they would all fail.

When the course ended, the university unanimously nominated Laurence Nagel as the representative to report the results to Professor Peterson . The result was CANCER ( Computer Analysis of Nonlinear Circuits, Excluding Radiation ), which was recognized by Professor Peterson .

In the fall of 1971 , CANCER was renamed SPICE and sent to friendly users . On April 12 , 1973 , Professor Donald O. Peterson introduced the SPICE paper at the Sixteenth Midwest Symposium on Circuit Theory , and SPICE began to be known to the world.

The first version was developed in 1971 by seven graduate students including Laurence Nagel under the guidance of Professor Ronald A. Rohrer , who announced it in a paper published at the 1971 International Solid-State Circuits Conference ( ISSCC ). In 1975 , the official practical version was launched under the guidance of Professor Donald O. Peterson. SPICE2G.6 , released in 1983 , has been an industrial standard for a long time. It contains more than 15,000 FORTRON statements and runs on a variety of small and medium-sized computers. SPICE3 was launched in 1985 and switched to C language development. It is easy to run on UNIX workstations. Graphical post-processing tools and schematic tools are also added, providing more device models and analysis functions. It was designated as the US national industrial standard in 1988 and is mainly used for the design and simulation of electronic systems such as analog circuits, mixed analog and digital circuits, and power circuits.

The seven talented students are: Laurence W. Nagel ( UC Berkeley , BA 1969 , MA 1970 , PhD 1975 ), Bob Berry , Shi-Ping Fan , Frank Jenkins , Jesse Pipkin , Steve Ratner and Lynn Weber .

The significance of SPICE

Before SPICE , designers analyzed circuits with either pen and paper or breadboard . Professor Donald O. Peterson was called "Professor Envelope" by his students because he believed that circuit analysis could be done on the back of an envelope. However, as the scale of circuits increased, it became increasingly impossible to use pen and paper, and breadboards could not accurately reflect the circuit characteristics on the chip, and the cost was also increasing.

The design of electronic products usually starts with a functional block diagram, then refines it to a schematic diagram, and then goes through a very complex and tedious debugging and verification process before it can be completed. In order to verify the correctness of the schematic diagram, a test board (sample board) must be welded, or a "breadboard " that is easy to plug in must be used . Each node must be correct and reliable. The connection or welding process is a meticulous and time-consuming task, which is almost impossible to complete when there are many devices. Each adjustment requires proofing, which is time-consuming and costly. This is especially true when designing integrated circuits. It is urgent to verify the function of the integrated circuit before manufacturing. This practical need forces people to find other ways to solve it.

According to circuit theory, people can establish node equations and loop equations, and get results by solving the system of equations composed of these equations, that is, the working conditions of the circuit can be obtained through calculation. However, the circuit containing devices such as inductors and capacitors forms a set of differential equations, and manual calculation is still a tiring job, while computers can show their talents and easily complete it through their powerful storage, calculation and graphic display capabilities, and get results quickly.

It is becoming increasingly urgent to use software to simulate circuits. Based on this idea, people developed circuit simulation software, which can replace time-consuming and tiring repeated adjustments through fast simulation, improve design speed and efficiency, and save time and cost. The earliest and most outstanding simulation software is SPICE .

Many basic elements in SPICE come from the "Circuit Synthesis" course taught by Professor Rohrer , including the module for solving sparse matrices (which increases the scale of processable circuits by several times) and the use of implicit integration algorithms (which makes transient analysis more stable). In addition, the program has built-in semiconductor device models, so users only need to provide a set of model parameters, and there is no need to provide the FORTRAN module of the device model themselves.

SPICE was more than a simple program for teaching. It was the first to incorporate sparse matrix analysis to allow economical simulation of large circuits, adjoint analysis of sensitivity to component variations and noise, built-in device models for "first cut" design, and a simple user interface that evolved through the transition from punched cards to dumb terminals to sophisticated workstations. SPICE 's developers made source code widely available for the first time, enabling others to contribute more sophisticated device models and additional analysis capabilities. These factors contributed to its dominance in the subsequent development of both open source and proprietary circuit simulation software.

SPICE is the pioneer of open source code

There were many open source codes at that time, but none of them had much commercial value. SPICE was different. Some people had already seen its commercial value, but Professor Peterson insisted on making the code open source. We all have to thank Professor Peterson sincerely . Anyone can get the source code of SPICE for a $ 20 handling fee . Of course, during the Cold War, SPICE was banned from export to what the government considered to be "communist countries."

Development of SPICE

Since the advent of SPICE , its versions have been continuously updated, including SPICE2 , SPICE2G6 , SPICE3 , SPICE3f5 and other versions. The new versions have been mainly enhanced in circuit input, graphics, data structure and execution efficiency. The industry generally believes that SPICE2G6 is the most successful and effective. Subsequent versions are only partial changes. Various commonly used SPICE tools are now based on the publicly released SPICE 2G6 source code.

In the more than 50 years from the 1970s to today, SPICE has made amazing achievements, from being able to simulate only a dozen components to being able to simulate circuits with tens of millions of components today. SPICE is a tool for solving nonlinear ordinary differential equations, but because it is difficult to change the cornerstone of SPICE , SPICE did not change much in the mid -1990s .

The cornerstones of SPICE include: Modified Nodal Analysis , Sparse Matrix Solver , Newton -Raphson Iteration , Implicit Numerical Integration , Dynamic Time Step Control , Local Truncation Error , etc.

Currently , the mainstream commercial SPICE include HSPICE & FineSim SPICE from Synopsys, Spectre & APS from Cadence , ELDO & AFS from Siemens EDA , Smart - Spice from Silvaco , ALPS from domestic manufacturer Empyrean and NanoSpice & NanoSpice Giga from Primarius are competitive to a certain extent.

Of course, in addition to the commercial SPICE provided by EDA companies , there are also some established semiconductor companies that develop their own SPICE internally , which are not for sale, including IBM , Intel , Texas Instruments ( TI ), Analog Devices ( ADI ), STMicroelectronics ( STM ) and Infineon . The SPICE of these semiconductor companies basically has its own device models. It is reported that TI has now made its internal SPICE open source.

The advantage of SPICE is its accuracy, but its disadvantages are also obvious. There are certain limitations on the scale and speed of simulation, and it is generally used for small-scale and high-precision simulation applications. Therefore , another type of transistor-level simulator FastSPICE was developed on this basis , such as NanoSim , HSIM ( Nassda acquired in 2004 ), FineSim Pro ( Magma acquired in 2011 ) and CustomSim ( XA ) from Synopsys; UltraSim ( Cadence acquired Celestry in 2003. It should be mentioned here that UltraSim was first developed by BTA . BTA was founded by the Prologic Design team and Professor Hu Zhengming in 1993. BTA merged with Dr. Dai Weimin's Ultima to form Celestry in 2001 ) and Spectre XPS from Cadence; ADiT from Siemens EDA ( EverCAD acquired in 2006 ), NanoSpice Giga from Prologic Design, etc., are used to handle large-scale circuit simulation and full-chip verification. FastSPICE uses a lot of acceleration simulation technologies, such as Table Model and Event Driven circuit partition , and simplifies the circuit to handle large-scale circuit simulation needs at the expense of certain simulation accuracy, such as customized digital circuits, memory, SOC full-chip simulation and verification. In actual applications, SPICE is often used for high-precision analog circuits and small-module customized digital circuits and memory modules, while FastSPICE is often used for large-scale post-simulation circuits, large-module customized digital circuits, memory, and full-chip SOC simulation and verification.

SPICE in China

It is worth mentioning that domestic EDA companies have made significant progress in SPICE .

In 2016 , NanoSpice Giga of ProPlus Electronics proposed a new concept, GigaSpice , which replaced the application of FastSPICE with the engine and precision of SPICE to avoid the loss of precision caused by FastSPICE , and provided faster speed than FastSPICE . It has been recognized and applied in the international market in the industry-leading ultra-large-scale memory design and large-scale post-simulation circuits.

In 2018 , HuaDa Empyrean officially launched the industry's first heterogeneous parallel simulation system, Empyrean ALPS-GT ™. Based on a large computing power heterogeneous platform and the original heterogeneous intelligent matrix solving technology SMS-GT , it greatly improved the performance of circuit simulation, maintained 100% True SPICE accuracy, and improved the performance by more than 10 times compared to CPU- based SPICE . The launch of ALPS-GT solves the problem that FastSPICE and spice with fastspice technology are not accurate enough, while traditional SPICE and parallel SPICE have insufficient performance and capacity.

Open Source SPICE

Finally, it is necessary to talk about the open source NGSPICE . Since the 1990s, a group of SPICE enthusiasts and universities have taken over SPICE3f5 and integrated several other open source software, including xspice , cider , gss , adms , etc., to build NGSPICE .

NGSPICE is a general-purpose circuit simulation program suitable for nonlinear and linear analyses . Circuits can contain resistors , capacitors, inductors , mutual inductors , independent or dependent voltage and current sources, loss - less and lossy transmission lines , switches , uniform distributed RC lines , and the five most common semiconductor devices: diodes, bipolar transistors (BJT), junction field effect transistors ( JFET ) , metal semiconductor field effect transistors ( MESFET ) , and metal oxide semiconductor field effect transistors (MOSFET) . .

NGSPICE is an update to SPICE3f5 , the last release of the SPICE3 simulator series from UC Berkeley . NGSPICE adds many new features and fixes many of the bugs in SPICE3f5 . Developing a complex software like a circuit simulator is very difficult , and most of the work, in addition to adding new features, is bug fixing and code refactoring .

NGSPICE has built-in models for semiconductor devices . Users only need to set relevant model parameter values to use them.

NGSPICE supports mixed - level simulation and provides a direct link between technology parameters and circuit performance . Mixed -level circuit and device simulation can provide greater simulation accuracy than stand-alone circuit or device simulator by numerically modeling key components in the circuit. Compact models can be used in other devices. The extension of mixed models in NGSPICE is CIDER , an integrated simulation that mixes circuit level and device level.

NGSPICE supports mixed-signal simulation by integrating XSPICE . XSPICE software was developed by the Georgia Institute of Technology as an extension of SPICE3C1 . It has now been ported into NGSPICE and enhanced to provide board level and mixed - signal simulation.

XSPICE extensions also support pure digital simulation .

NGSPICE is evolving slowly, but much slower than commercial SPICE . Currently, it is being used in many academic research.

refer to:

1. Brief introduction and installation of ngspice , author: dc lin

2. Seven EDA technology tools that promote IC design revolution , author: Zhao Yuanchuang

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