Massachusetts Institute of TechnologyDepartment of Electrical Engineering and Computer Science6.012Electronic Devices and CircuitsFall 1995Introduction to Circuit Simulation for 6.012[ Written by Rod Hinman, Fall 1993. Revised by Tracy Adams and Yakov Royter,Spring 1994, and Siva Narendra, Fall 1995]HSPICE is an analysis tool to study circuits ranging from diode protection networks to bipolar transistor am-plifiers to logic gates. HSPICE is a fairly straightforward simulation tool, provided you take the time to read the infor-mation presented in this package. The purpose of this handout is to introduce you to the programs you will be using.In this handout you will find the following: an explanation of the basics of SPICE, a circuit simulation pro-gram developed at UC Berkeley in the early 1970s; example simulation files and an explanation of how to run them;a description of some of the enhancements of HSPICE, a commercial version of SPICE which we will be using; andinformation using HSPICE on ATHENA.After you have read through the information here, go through the example circuit making sure that you un-derstand how each circuit component is represented in the SPICE model. Simulate it yourself to get practice creatinginput files and using GSI, the graphical output package. If you have problems, be sure to see one of the TAs.1 Generic SPICEThe input files to HSPICE can be created using EMACS (or VI). If you are not familiar with one of these editors, besure to attend one of the ATHENA minicourses offered and/or get a hold of a manual for EMACS (or VI). SPICE wasoriginally created when punchcards were the primary method of computer input. Each circuit element was describedon a separate card, or sometimes on several adjacent cards. Because of this, individual lines in the input files are some-times referred to as “cards,” and the whole file as the “SPICE deck.”Each input file to HSPICE begins with a title line. The first line of the file is taken as the title whether youintended it to be or not! If a title is not given, the first line specifying your circuit will be assumed as the title and yoursimulation results will be erroneous (or more likely, the simulation won’t run).Each input file should end with an .END statement. This is needed to tell HSPICE that the input file has end-ed. Without the .END statement, the simulation will not run. Be sure that there is a newline (or return) after that last.END, some SPICE programs need to have the final newline.After giving a title line, the ordering of the remaining information needed within the file is fairly arbitrary(except for the .END statement). There is no convention for listing circuit components in any particular order withinthe file. One possible convention for listing information within a SPICE input file is shown in the example file includedin this package. Note that SPICE is not case sensitive, so .end and .END are the same thing.Table 1 Example CircuitBefore creating an input file for HSPICE, you should label each node of the circuit that you wish to simulatewith a different number (see the example circuit above). The numbers given to each node will serve to specify the to-pology of the circuit by defining interconnections between different components. There are no set rules for how to de-fine each node; HOWEVER, be sure that two separate nodes are not labeled with the same number as this will produceerroneous results in your simulation. The general convention is to label the ground node as NODE 0. After the nodesin the circuit have been labeled, the location of different circuit components can be specified by giving the two (orthree, etc.) nodes which a particular component is attached to. For example, a resistor is specified byRxxxx N1 N2 ValueThe xxxx can be any alphanumeric string. The N1 and N2 are the two nodes at which the resistor is connectedand Value specifies the size of the resistance. For example (from the circuit above), R1 would be entered as:R1 3 0 5KThe R1 specifies that the component is a resistor, the 3 0 specifies that the resistor is connected betweennode 3 and node 0. and 5K specifies that the resistor value is 5kΩ. Capacitors are entered in a similar way, their namemust start with C.Component values and parameters may be specified in three formats: a normal number, exponential notation,or with a scale factor. An example of exponential notation is 1.5e3 which is equivalent to 1500. You may also use acharacter following the number to represent multiplication by a power of ten. Thus 1.5k is also equivalent to 1500. Thefollowing table shows the different scale factors. Note that except for the combination meg, other characters after themultiplier character are ignored. Thus 5ns is 5δ7 10-9but does not explicitly represent seconds.Abbrev. Multiplier Abbrev. MultiplierT 1e12 M 1e-3G 1e9 U 1e-6MEG 1e6 N 1e-9K 1e3 P 1e-12 F 1e-15Some components used in a circuit require a .model specification (such as a diode or transistor). The.model statement sets the model parameters for a given device. As an example, the .model specification for thediode used in the circuit above is.model diode1 D level=1 IS=1e-14 CJO=1e-12 M=.5 TT=3e-11 VJ=.783+ VB=30The diode1 is the name for the model, while D specifies the device type. Other device types you will likelyencounter include nmos, pmos, npn, and pnp transistors.These specifications are followed by the device parameters, in any order. level=1 specifies the particularequations to use when modeling the diode. Level 1 is the simplest, and corresponds closely to the equations we areusing in class. There are many other models to take second order effects into account. IS (amps) is the reverse satu-ration current of the diodes, CJO (F) is the depletion capacitance at zero bias voltage. M is a parameter that HSPICEuses to calculate non-zero bias junction capacitance, and its dependence on the doping profile. In 6.012, this parameteris equal to 0.5. TT (sec) is the transit time, related to the diffusion capacitance, and VJ (Volts) is the built in potential.The first character of the next line is a + character, which means that the line is just a continuation of the previous one.You may use as many continuation lines as you need to complete a statement. The last of the parameter is VB (Volts),which is the reverse breakdown voltage.The diode in the circuit above is specified by the line:d1 2 3 diode1The d1 is the name of the diode. The diode1
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