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1 SPICE 3A6 User's Guide December 15, 1985 T. Quarles A.R.Newton, D.O.Pederson, A.Sangiovanni-Vincentelli Department of Electrical Engineering and Computer Sciences University of California Berkeley, Ca., 94720 ____________________________________________________ 2 | | | Please Note | | | | | | This is an update to the first release of| | SPICE3 and the development of SPICE and its algo-| | rithms is ongoing at Berkeley. We believe that| | all of the features described here are fully func-| | tional; however, not all of the intended capabili-| | ties of the program have been implemented in full| | yet. Please mail any reports of suspected bugs in| | the program or suggested enhancements to the pro-| | gram to: | | | | EECS/ERL Industrial Support Office | | 461 Cory Hall | | U.C. Berkeley | | Berkeley, Ca. 94720 | | | | or by electronic mail to: | | | | spice@cad.BERKELEY.EDU (ARPAnet, CSnet) | | ucbvax!ucbcad!spice (UUCPnet) | | | | | | Please include input to the program, out- | | put, suggestions as to where the problem may | | be, and if possible, a suggested fix! | | | | SPICE3 has been in beta-test since April | | 1985 and has been in use at over twenty sites. | | This version is the result of our own work at | | Berkeley and the feedback we have received | | from our beta sites. We thank them for their | | help. | |___________________________________________________| SPICE is a general-purpose circuit simulation program for nonlinear dc, nonlinear transient, and linear ac analyses. Cir- cuits may contain resistors, capacitors, inductors, mutual induc- tors, independent voltage and current sources, four types of dependent sources, transmission lines, and the four most common 3 semiconductor devices: diodes, BJT's, JFET's, and MOSFET's. The SPICE3 version is based directly on SPICE 2G.6. While SPICE3 is being developed to include new features, it will con- tinue to support those capabilities and models which remain in extensive use in the SPICE2 program. SPICE has built-in models for the semiconductor devices, and the user need specify only the pertinent model parameter values. The model for the BJT is based on the integral charge model of Gummel and Poon; however, if the Gummel- Poon parameters are not specified, the model reduces to the simpler Ebers-Moll model. In either case, charge storage effects, ohmic resistances, and a current-dependent output conductance may be included. The diode model can be used for either junction diodes or Schottky barrier diodes. The JFET model is based on the FET model of Shichman and Hodges. Four MOSFET models are implemented: MOS1 is described by a square-law I-V characteristic, MOS2[1] is an analytical model, while MOS3[1] is a semi-empirical model, and MOS4[2,3] is the new BSIM (Berkeley Short-channel IGFET Model). MOS2, MOS3, and MOS4 include second-order effects such as channel length modulation, subthreshold conduction, scattering limited velocity saturation, small-size effects, and charge-controlled capacitances. 4 1. TYPES OF ANALYSIS 1.1. DC Analysis The dc analysis portion of SPICE determines the dc operating point of the circuit with inductors shorted and capacitors opened. A dc analysis is automatically performed prior to a transient analysis to determine the transient initial conditions, and prior to an ac small-signal analysis to determine the linear- ized, small-signal models for nonlinear devices. The dc analysis can also be used to generate dc transfer curves: a specified independent voltage or current source is stepped over a user- specified range and the dc output variables are stored for each sequential source value. 1.2. AC Small-Signal Analysis The ac small-signal portion of SPICE computes the ac output variables as a function of frequency. The program first computes the dc operating point of the circuit and determines linearized, small-signal models for all of the nonlinear devices in the cir- cuit. The resultant linear circuit is then analyzed over a user-specified range of frequencies. The desired output of an ac small- signal analysis is usually a transfer function (voltage gain, transimpedance, etc). If the circuit has only one ac input, it is convenient to set that input to unity and zero 5 phase, so that output variables have the same value as the transfer function of the output variable with respect to the input. 1.3. Transient Analysis The transient analysis portion of SPICE computes the tran- sient output variables as a function of time over a user- specified time interval. The initial conditions are automati- cally determined by a dc analysis. All sources which are not time dependent (for example, power supplies) are set to their dc value. The transient time interval is specified on a .TRAN con- trol line. 2. CONVERGENCE Both dc and transient solutions are obtained by an iterative process which is terminated when both of the following conditions hold: 1) The nonlinear branch currents converge to within a tolerance of 0.1 percent or 1 picoamp (1.0E-12 Amp), whichever is larger. 2) The node voltages converge to within a tolerance of 0.1 per- cent or 1 microvolt (1.0E-6 Volt), whichever is larger. 6 Although the algorithm used in SPICE has been found to be very reliable, in some cases it will fail to converge to a solu- tion. When this failure occurs, the program will terminate the job. Failure to converge in dc analysis is usually due to an error in specifying circuit connections, element values, or model parameter values. Regenerative switching circuits or circuits with positive feedback probably will not converge in the dc analysis unless the OFF option is used for some of the devices in the feedback path, or the .NODESET card is used to force the cir- cuit to converge to the desired state. 3. INPUT FORMAT The input format for SPICE is of the free format type. Fields on a card are separated by one or more blanks, a comma, an equal (=) sign, or a left or right parenthesis; extra spaces are ignored. A card may be continued by entering a + (plus) in column 1 of the following card; SPICE continues reading begin- ning with column 2. A name field must begin with a letter (A through Z) and can- not contain any delimiters. 7 A number field may be an integer field (12, -44), a floating point field (3.14159), either an integer or floating point number followed by an integer exponent (1E-14, 2.65E3), or either an integer or a floating point number followed by one of the follow- ing scale factors: T=1E12 G=1E9 MEG=1E6 K=1E3 MIL=25.4E-6 M=1E-3 U=1E-6 N=1E-9 P=1E-12 F=1E-15 Letters immediately following a number that are not scale factors are ignored, and letters immediately following a scale factor are ignored. Hence, 10, 10V, 10VOLTS, and 10HZ all represent the same number, and M, MA, MSEC, and MMHOS all represent the same scale factor. Note that 1000, 1000.0, 1000HZ, 1E3, 1.0E3, 1KHZ, and 1K all represent the same number. 4. CIRCUIT DESCRIPTION The circuit to be analyzed is described to SPICE by a set of element cards, which define the circuit topology and element values, and a set of control cards, which define the model param- eters and the run controls. The first card in the input deck must be a title card, and the last card must be a .END card. The order of the remaining cards is arbitrary (except, of course, that continuation cards must immediately follow the card being 8 continued). Each element in the circuit is specified by an element card that contains the element name, the circuit nodes to which the element is connected, and the values of the parameters that determine the electrical characteristics of the element. The first letter of the element name specifies the element type. The format for the SPICE element types is given in what follows. The strings XXXXXXX, YYYYYYY, and ZZZZZZZ denote arbitrary alphanumeric strings. For example, a resistor name must begin with the letter R and can contain one or more characters. Hence, R, R1, RSE, ROUT, and R3AC2ZY are valid resistor names. Data fields that are enclosed in less than and greater than signs '< >' are optional. All indicated punctuation (parentheses, equal signs, etc.) is optional and merely indicate the presence of any delimiter. A consistent style such as that shown here will make the input easier to understand. With respect to branch voltages and currents, SPICE uniformly uses the associated reference convention (current flows in the direction of voltage drop). Nodes names may be arbitrary character strings. The datum (ground) node must be named '0'. The circuit cannot contain a loop of voltage sources and/or inductors and cannot contain a cutset of current sources and/or capacitors. Each node in the circuit must have a dc path to ground. Every node must have at 9 least two connections except for transmission line nodes (to per- mit unterminated transmission lines) and MOSFET substrate nodes (which have two internal connections anyway). 5. TITLE CARD, COMMENT CARDS AND .END CARD 5.1. Title Card Examples: POWER AMPLIFIER CIRCUIT TEST OF CAM CELL This card must be the first card in the input deck. Its contents are printed verbatim as the heading for each section of output. 5.2. .END Card Examples: .END This card must always be the last card in the input deck. Note that the period is an integral part of the name. 10 5.3. Comment Card General Form: * <any comment> Examples: * RF=1K GAIN SHOULD BE 100 * MAY THE FORCE BE WITH MY CIRCUIT The asterisk in the first column indicates that this card is a comment card. Comment cards may be placed anywhere in the cir- cuit description. 6. ELEMENT CARDS 6.1. Resistors General form: RXXXXXXX N1 N2 VALUE Examples: R1 1 2 100 RC1 12 17 1K N1 and N2 are the two element nodes. VALUE is the resis- tance (in ohms) and may be positive or negative but not zero. 11 6.2. Capacitors and Inductors General form: CXXXXXXX N+ N- VALUE <IC=INCOND> LYYYYYYY N+ N- VALUE <IC=INCOND> Examples: CBYP 13 0 1UF COSC 17 23 10U IC=3V LLINK 42 69 1UH LSHUNT 23 51 10U IC=15.7MA N+ and N- are the positive and negative element nodes, respectively. VALUE is the capacitance in Farads or the induc- tance in Henries. For the capacitor, the (optional) initial condition is the initial (time-zero) value of capacitor voltage (in Volts). For the inductor, the (optional) initial condition is the initial (time-zero) value of inductor current (in Amps) that flows from N+, through the inductor, to N-. Note that the initial condi- tions (if any) apply 'only' if the UIC option is specified on the .TRAN card. 6.3. Coupled (Mutual) Inductors General form: KXXXXXXX LYYYYYYY LZZZZZZZ VALUE 12 Examples: K43 LAA LBB 0.999 KXFRMR L1 L2 0.87 LYYYYYYY and LZZZZZZZ are the names of the two coupled inductors, and VALUE is the coefficient of coupling, K, which must be greater than 0 and less than or equal to 1. Using the 'dot' convention, place a 'dot' on the first node of each induc- tor. 6.4. Transmission Lines (Lossless) General form: TXXXXXXX N1 N2 N3 N4 Z0=VALUE <TD=VALUE> <F=FREQ <NL=NRMLEN>> + <IC=V1,I1,V2,I2> Examples: T1 1 0 2 0 Z0=50 TD=10NS N1 and N2 are the nodes at port 1; N3 and N4 are the nodes at port 2. Z0 is the characteristic impedance. The length of the line may be expressed in either of two forms. The transmis- sion delay, TD, may be specified directly (as TD=10ns, for exam- ple). Alternatively, a frequency F may be given, together with NL, the normalized electrical length of the transmission line with respect to the wavelength in the line at the frequency F. 13 If a frequency is specified but NL is omitted, 0.25 is assumed (that is, the frequency is assumed to be the quarter-wave fre- quency). Note that although both forms for expressing the line length are indicated as optional, one of the two must be speci- fied. Note that this element models only one propagating mode. If all four nodes are distinct in the actual circuit, then two modes may be excited. To simulate such a situation, two transmission- line elements are required. (see the example in Appendix A for further clarification.) The (optional) initial condition specification consists of the voltage and current at each of the transmission line ports. Note that the initial conditions (if any) apply 'only' if the UIC option is specified on the .TRAN card. 6.5. Linear Dependent Sources SPICE allows circuits to contain linear dependent sources characterized by any of the four equations i=g*v v=e*v i=f*i v=h*i where g, e, f, and h are constants representing transconductance, voltage gain, current gain, and transresistance, respectively. 14 6.6. Linear Voltage-Controlled Current Sources General form: GXXXXXXX N+ N- NC+ NC- VALUE Examples: G1 2 0 5 0 0.1MMHO N+ and N- are the positive and negative nodes, respectively. Current flow is from the positive node, through the source, to the negative node. NC+ and NC- are the positive and negative controlling nodes, respectively. VALUE is the transconductance (in mhos). 6.7. Linear Voltage-Controlled Voltage Sources General form: EXXXXXXX N+ N- NC+ NC- VALUE Examples: E1 2 3 14 1 2.0 N+ is the positive node, and N- is the negative node. NC+ and NC- are the positive and negative controlling nodes, respec- tively. VALUE is the voltage gain. 15 6.8. Linear Current-Controlled Current Sources General form: FXXXXXXX N+ N- VNAM VALUE Examples: F1 13 5 VSENS 5 N+ and N- are the positive and negative nodes, respectively. Current flow is from the positive node, through the source, to the negative node. VNAM is the name of a voltage source through which the controlling current flows. The direction of positive controlling current flow is from the positive node, through the source, to the negative node of VNAM. VALUE is the current gain. 6.9. Linear Current-Controlled Voltage Sources General form: HXXXXXXX N+ N- VNAM VALUE Examples: HX 5 17 VZ 0.5K N+ and N- are the positive and negative nodes, respectively. VNAM is the name of a voltage source through which the control- ling current flows. The direction of positive controlling 16 current flow is from the positive node, through the source, to the negative node of VNAM. VALUE is the transresistance (in ohms). 6.10. Independent Sources General form: VXXXXXXX N+ N- <<DC> DC/TRAN VALUE> <AC <ACMAG <ACPHASE>>> IYYYYYYY N+ N- <<DC> DC/TRAN VALUE> <AC <ACMAG <ACPHASE>>> Examples: VCC 10 0 DC 6 VIN 13 2 0.001 AC 1 SIN(0 1 1MEG) ISRC 23 21 AC 0.333 45.0 SFFM(0 1 10K 5 1K) VMEAS 12 9 N+ and N- are the positive and negative nodes, respectively. Note that voltage sources need not be grounded. Positive current is assumed to flow from the positive node, through the source, to the negative node. A current source of positive value, will force current to flow out of the N+ node, through the source, and into the N- node. Voltage sources, in addition to being used for circuit excitation, are the 'ammeters' for SPICE, that is, zero valued voltage sources may be inserted into the circuit for the purpose of measuring current. They will, of course, have no effect on circuit operation since they represent short-circuits. 17 DC/TRAN is the dc and transient analysis value of the source. If the source value is zero both for dc and transient analyses, this value may be omitted. If the source value is time-invariant (e.g., a power supply), then the value may option- ally be preceded by the letters DC. ACMAG is the ac magnitude and ACPHASE is the ac phase. The source is set to this value in the ac analysis. If ACMAG is omitted following the keyword AC, a value of unity is assumed. If ACPHASE is omitted, a value of zero is assumed. If the source is not an ac small-signal input, the keyword AC and the ac values are omitted. Any independent source can be assigned a time-dependent value for transient analysis. If a source is assigned a time- dependent value, the time-zero value is used for dc analysis. There are five independent source functions: pulse, exponential, sinusoidal, piece-wise linear, and single-frequency FM. If parameters other than source values are omitted or set to zero, the default values shown will be assumed. (TSTEP is the printing increment and TSTOP is the final time (see the .TRAN card for explanation)). 1. Pulse PULSE(V1 V2 TD TR TF PW PER) Examples: 18 VIN 3 0 PULSE(-1 1 2NS 2NS 2NS 50NS 100NS) parameters default values units V1 (initial value) Volts or Amps V2 (pulsed value) Volts or Amps TD (delay time) 0.0 seconds TR (rise time) TSTEP seconds TF (fall time) TSTEP seconds PW (pulse width) TSTOP seconds PER(period) TSTOP seconds A single pulse so specified is described by the following table: time value 0 V1 TD V1 TD+TR V2 TD+TR+PW V2 TD+TR+PW+TF V1 TSTOP V1 Intermediate points are determined by linear interpolation. 2. Sinusoidal SIN(VO VA FREQ TD THETA) Examples: VIN 3 0 SIN(0 1 100MEG 1NS 1E10) parameters default value units VO (offset) Volts or Amps VA (amplitude) Volts or Amps 19 FREQ (frequency) 1/TSTOP Hz TD (delay) 0.0 seconds THETA (damping factor) 0.0 1/seconds The shape of the waveform is described by the following table: time value 0 to TD VO TD to TSTOP VO + VA*exp(-(time-TD)*THETA)*sine(twopi*FREQ*(time+TD)) 3. Exponential EXP(V1 V2 TD1 TAU1 TD2 TAU2) Examples: VIN 3 0 EXP(-4 -1 2NS 30NS 60NS 40NS) parameters default values units V1 (initial value) Volts or Amps V2 (pulsed value) Volts or Amps TD1 (rise delay time) 0.0 seconds TAU1 (rise time constant) TSTEP seconds TD2 (fall delay time) TD1+TSTEP seconds TAU2 (fall time constant) TSTEP seconds The shape of the waveform is described by the following table: time value 0 to TD1 V1 TD1 to TD2 V1+(V2-V1)*(1-exp(-(time-TD1)/TAU1)) TD2 to TSTOP V1+(V2-V1)*(1-exp(-(time-TD1)/TAU1)) 20 +(V1-V2)*(1-exp(-(time-TD2)/TAU2)) 4. Piece-Wise Linear PWL(T1 V1 <T2 V2 T3 V3 T4 V4 ...>) Examples: VCLOCK 7 5 PWL(0 -7 10NS -7 11NS -3 17NS -3 18NS -7 50NS -7) Parameters and default values Each pair of values (Ti, Vi) specifies that the value of the source is Vi (in Volts or Amps) at time=Ti. The value of the source at intermediate values of time is determined by using linear interpolation on the input values. 5. Single-Frequency FM SFFM(VO VA FC MDI FS) Examples: V1 12 0 SFFM(0 1M 20K 5 1K) parameters default values units VO (offset) Volts or Amps VA (amplitude) Volts or Amps FC (carrier frequency) 1/TSTOP Hz MDI (modulation index) FS (signal frequency) 1/TSTOP Hz The shape of the waveform is described by the following equation: 21 value = VO + VA*sine((twopi*FC*time) + MDI*sine(twopi*FS*time)) 6.11. Switches General form: SXXXXXXX N+ N- NC+ NC- MODEL <ON><OFF> WYYYYYYY N+ N- VNAM MODEL <ON><OFF> Examples: s1 1 2 3 4 switch1 ON s2 5 6 3 0 sm2 off Switch1 1 2 10 0 smodel1 w1 1 2 vclock switchmod1 W2 3 0 vramp sm1 ON wreset 5 6 vclck lossyswitch OFF Nodes 1 and 2 are the nodes between which the switch termi- nals are connected. The model name is mandatory while the ini- tial conditions are optional. For the voltage controlled switch, nodes 3 and 4 are the positive and negative controlling nodes respectively. For the current controlled switch, the controlling current is that through the specified voltage source. The direc- tion of positive controlling current flow is from the positive node, through the source, to the negative node. 22 7. SEMICONDUCTOR DEVICES The elements described to this point typically require only a few parameter values. However, the models for the semiconduc- tor devices that are included in the SPICE program require many parameter values. Often, many devices in a circuit are defined by the same set of device model parameters. For these reasons, a set of device model parameters is defined on a separate .MODEL card and assigned a unique model name. The device element cards in SPICE then refer to the model name. This scheme alleviates the need to specify all of the model parameters on each device element card. Each device element card contains the device name, the nodes to which the device is connected, and the device model name. In addition, other optional parameters may be specified for some devices: geometric factors and an initial condition. The area factor used on the diode, BJT and JFET device cards determines the number of equivalent parallel devices of a speci- fied model. The affected parameters are marked with an asterisk under the heading 'area' in the model descriptions below. Several geometric factors associated with the channel and the drain and source diffusions can be specified on the MOSFET device card. 23 Two different forms of initial conditions may be specified for some devices. The first form is included to improve the dc convergence for circuits that contain more than one stable state. If a device is specified OFF, the dc operating point is deter- mined with the terminal voltages for that device set to zero. After convergence is obtained, the program continues to iterate to obtain the exact value for the terminal voltages. If a cir- cuit has more than one dc stable state, the OFF option can be used to force the solution to correspond to a desired state. If a device is specified OFF when in reality the device is conduct- ing, the program will still obtain the correct solution (assuming the solutions converge) but more iterations will be required since the program must independently converge to two separate solutions. The .NODESET card serves a similar purpose as the OFF option. The .NODESET option is easier to apply and is the pre- ferred means to aid convergence. The second form of initial conditions are specified for use with the transient analysis. These are true 'initial conditions' as opposed to the convergence aids above. See the description of the .IC card and the .TRAN card for a detailed explanation of initial conditions. 7.1. Semiconductor Resistors General form: 24 RXXXXXXX N1 N2 <VALUE> <MNAME> <L=LENGTH> <W=WIDTH> Examples: RLOAD 2 10 10K RMOD 3 7 RMODEL L=10u W=1u This is the more general form of the resistor presented in section 6.1, and allows the modeling of temperature effects and for the calculation of the actual resistance value from strictly geometric information and the specifications of the process. If VALUE is specified, it overrides the geometric information and defines the resistance. If MNAME is specified, then the resis- tance may be calculated from the process information in the model MNAME and the given LENGTH and WIDTH. If VALUE is not specified, then MNAME and LENGTH must be specified. If WIDTH is not speci- fied, then it will be taken from the default width given in the model. 7.2. Semiconductor Capacitors General form: CXXXXXXX N1 N2 <VALUE> <MNAME> <L=LENGTH> <W=WIDTH> <IC=VAL> Examples: CLOAD 2 10 10P CMOD 3 7 CMODEL L=10u W=1u 25 This is the more general form of the Capacitor presented in section 6.2, and allows for the calculation of the actual capaci- tance value from strictly geometric information and the specifi- cations of the process. If VALUE is specified, it defines the capacitance. If MNAME is specified, then the capacitance is cal- culated from the process information in the model MNAME and the given LENGTH and WIDTH. If VALUE is not specified, then MNAME and LENGTH must be specified. If WIDTH is not specified, then it will be taken from the default width given in the model. Either VALUE or MNAME, LENGTH, and WIDTH may be specified, but not both sets. 7.3. Uniform Distributed RC Lines (Lossy) General form: UXXXXXXX N1 N2 N3 MNAME L=LEN <N=LUMPS> Examples: U1 1 2 0 URCMOD L=50U URC2 1 12 2 UMODL l=1MIL N=6 N1 and N2 are the two element nodes the RC line connects, while N3 is the node to which the capacitances are connected. MNAME is the model name, LEN is the length of the RC line in meters. LUMPS, if specified, is the number of lumped segments to use in modeling the RC line (see the model description for the 26 action taken if this parameter is omitted). 7.4. Junction Diodes General form: DXXXXXXX N+ N- MNAME <AREA> <OFF> <IC=VD> Examples: DBRIDGE 2 10 DIODE1 DCLMP 3 7 DMOD 3.0 IC=0.2 N+ and N- are the positive and negative nodes, respectively. MNAME is the model name, AREA is the area factor, and OFF indi- cates an (optional) starting condition on the device for dc analysis. If the area factor is omitted, a value of 1.0 is assumed. The (optional) initial condition specification using IC=VD is intended for use with the UIC option on the .TRAN card, when a transient analysis is desired starting from other than the quiescent operating point. 7.5. Bipolar Junction Transistors (BJT's) General form: QXXXXXXX NC NB NE <NS> MNAME <AREA> <OFF> <IC=VBE,VCE> Examples: Q23 10 24 13 QMOD IC=0.6,5.0 27 Q50A 11 26 4 20 MOD1 NC, NB, and NE are the collector, base, and emitter nodes, respectively. NS is the (optional) substrate node. If unspeci- fied, ground is used. MNAME is the model name, AREA is the area factor, and OFF indicates an (optional) initial condition on the device for the dc analysis. If the area factor is omitted, a value of 1.0 is assumed. The (optional) initial condition specification using IC=VBE,VCE is intended for use with the UIC option on the .TRAN card, when a transient analysis is desired starting from other than the quiescent operating point. See the .IC card description for a better way to set transient initial conditions. 7.6. Junction Field-Effect Transistors (JFET's) General form: JXXXXXXX ND NG NS MNAME <AREA> <OFF> <IC=VDS,VGS> Examples: J1 7 2 3 JM1 OFF ND, NG, and NS are the drain, gate, and source nodes, respectively. MNAME is the model name, AREA is the area factor, and OFF indicates an (optional) initial condition on the device for dc analysis. If the area factor is omitted, a value of 1.0 28 is assumed. The (optional) initial condition specification, using IC=VDS,VGS is intended for use with the UIC option on the .TRAN card, when a transient analysis is desired starting from other than the quiescent operating point. See the .IC card for a better way to set initial conditions. 7.7. MOSFET's General form: MXXXXXXX ND NG NS NB MNAME <L=VAL> <W=VAL> <AD=VAL> <AS=VAL> + <PD=VAL> <PS=VAL> <NRD=VAL> <NRS=VAL> <OFF> <IC=VDS,VGS,VBS> Examples: M1 24 2 0 20 TYPE1 M31 2 17 6 10 MODM L=5U W=2U M1 2 9 3 0 MOD1 L=10U W=5U AD=100P AS=100P PD=40U PS=40U ND, NG, NS, and NB are the drain, gate, source, and bulk (sub- strate) nodes, respectively. MNAME is the model name. L and W are the channel length and width, in meters. AD and AS are the areas of the drain and source diffusions, in sq-meters. Note that the suffix U specifies microns (1E-6 m) and P sq-microns (1E-12 sq-m). If any of L, W, AD, or AS are not specified, default values are used. The use of defaults simplifies input deck preparation, as well as the editing required if device geometries are to be changed. PD and PS are the perimeters of the drain and source junctions, in meters. NRD and NRS designate the equivalent number of squares of the drain and source 29 diffusions; these values multiply the sheet resistance RSH speci- fied on the .MODEL card for an accurate representation of the parasitic series drain and source resistance of each transistor. PD and PS default to 0.0 while NRD and NRS to 1.0. OFF indicates an (optional) initial condition on the device for dc analysis. The (optional) initial condition specification using IC=VDS,VGS,VBS is intended for use with the UIC option on the .TRAN card, when a transient analysis is desired starting from other than the quiescent operating point. See the .IC card for a better and more convenient way to specify transient initial con- ditions. 7.8. .MODEL Card General form: .MODEL MNAME TYPE(PNAME1=PVAL1 PNAME2=PVAL2 ... ) Examples: .MODEL MOD1 NPN (BF=50 IS=1E-13 VBF=50) The .MODEL card specifies a set of model parameters that will be used by one or more devices. MNAME is the model name, and type is one of the following ten types: R resistor model C capacitor model 30 URC Uniform Distributed RC model D diode model NPN NPN BJT model PNP PNP BJT model NJF N-channel JFET model PJF P-channel JFET model NMOS N-channel MOSFET model PMOS P-channel MOSFET model SW voltage controlled switch CSW current controlled switch Parameter values are defined by appending the parameter name, as given below for each model type, followed by an equal sign and the parameter value. Model parameters that are not given a value are assigned the default values given below for each model type. 7.9. Resistor Model The resistor model consists of process-related device data that allow the resistance to be calculated from geometric infor- mation and to be corrected for temperature. The parameters available are: name parameter units default example o TC1 first order temperature coeff. Z/oC2 0.0 - TC2 second order temperature coeff. Z/ C 0.0 - RSH sheet resistance Z/[] - 50 DEFW default width meters 1e-6 2e-6 NARROW narrowing due to side etching meters 0.0 1e-7 31 The sheet resistance is used with the narrowing parameter and L and W from the resistor card to determine the nominal resistance by the formula L-NARROW R=RSHx W-NARROW Defw is used to supply a default value for W if one is not speci- fied on the device card. If either RSH or L is not specified, then the standard default resistance value of 1k Z is used. After the nominal resistance is calculated, it is adjusted for temperature by the formula: RES(temp)=RES(tnom)x(1+TC1x(temp-tnom)+TC2*(temp-tnom)2) 7.10. Capacitor Model The capacitor model contains process information that may be used to compute the capacitance from strictly geometric informa- tion. name parameter units default example 2 CJ junction bottom capacitance F/meters - 5e-5 CJSW junction sidewall capacitance F/meters - 2e-11 DEFW default device width meters 1e-6 2e-6 NARROW narrowing due to side etching meters 0.0 1e-7 The capacitor has a capacitance computed as 32 CAP=CJx(LENGTH-NARROW)x(WIDTH-NARROW)+2xCJSWx(LENGTH+WIDTH-2*NARROW) 7.11. Uniform Distributed RC Model The URC model is derived from a model proposed by L. Gertzberrg in 1974. The model is accomplished by a subcircuit type expansion of the URC line into a network of lumped RC seg- ments with internally generated nodes. The RC segments are in a geometric progression, increasing toward the middle of the URC line, with K as a proportionality constant. The number of lumped segments used, if not specified on the URC line card, is deter- mined by the following formula: 2 | R C 2 |(K-1)| | log|Fmaxx x x2xJxl x| | | | L L | K | | N= _____________________________ logK The URC line will be made up strictly of resistor and capa- citor segments unless the ISPERL parameter is given a non-zero value, in which case the capacitors are replaced with reverse biased diodes with a zero-bias junction capacitance equivalent to the capacitance replaced, and with a saturation current of ISPERL amps per meter of transmission line and an optional series resis- tance equivalent to RSPERL ohms per meter. name parameter units default example area 33 1 K Propagation Constant - 2.0 1.2 - 2 FMAX Maximum Frequency of interest Hz 1.0G 6.5MEG - 3 RPERL Resistance per unit length Ohm/m 1000 10 - 4 CPERL Capacitance per unit length F/m 1.0E-15 1PF - 5 ISPERL Saturation Current per unit length Amp/m 0 - - 6 RSPERL Diode Resistance per unit length Ohm/m 0 - - 7.12. Switch Model The switch model allows an almost ideal switch to be described in SPICE. The switch is not quite ideal, in that the resistance can not change from 0 to infinity, but must always have a finite positive value. By proper selection of the on and off resistances, they can be effectively zero and infinity in comparison to other circuit elements. The parameters available are: name parameter units default switch VT threshold voltage Volts 0.0 S IT threshold current Amps 0.0 W VH hysteresis voltage Volts 0.0 S IH hysteresis current Amps 0.0 W RON on resistance Z 1.0 both ROFF off resistance Z 1/GMIN* both *(See the .OPTIONS card for a description of GMIN, its default value results is a off resistance of 1.0e+12 ohms.) The use of an ideal element that is highly non-linear such as a switch can cause large discontinuities to occur in the cir- 34 cuit node voltages. A rapid change such as that associated with a switch changing state can cause numerical roundoff or tolerance problems leading to erroneous results or timestep difficulties. The user of switches can improve the situation by taking the fol- lowing steps: First of all it is wise to set ideal switch impedences only high and low enough to be negligible with respect to other cir- cuit elements. Using switch impedences that are close to "ideal" in all cases will aggravate the problem of discontinuities men- tioned above. Of cource, when modeling real devices such as MOS- FETS, the on resistance should be adjusted to a realistic level depending on the size of the device being modelled. If a wide rango of ON to OFF resistance must be used in the switched (ROFF/RON >1e+12), then the tolerance on errors allowed during transient analysis should be decreased by using the .OPTIONS card and specifying TRTOL to be less than the default value of 7.0. When switches are placed around capacitors, then the option CHGTOL should also be reduced. Suggested values for these two options are 1.0 and 1e-16 respectively. These changes inform SPICE3 to be more careful around the switch points so that no errors are made due to the rapid change in the circuit. 35 7.13. Diode Model The dc characteristics of the diode are determined by the parameters IS and N. An ohmic resistance, RS, is included. Charge storage effects are modeled by a transit time, TT, and a nonlinear depletion layer capacitance which is determined by the parameters CJO, VJ, and M. The temperature dependence of the saturation current is defined by the parameters EG, the energy and XTI, the saturation current temperature exponent. Reverse breakdown is modeled by an exponential increase in the reverse diode current and is determined by the parameters BV and IBV (both of which are positive numbers). name parameter units default example area 1 IS saturation current A 1.0E-14 1.0E-14 * 2 RS ohmic resistance Ohm 0 10 * 3 N emission coefficient - 1 1.0 4 TT transit-time sec 0 0.1Ns 5 CJO zero-bias junction capacitance F 0 2PF * 6 VJ junction potential V 1 0.6 7 M grading coefficient - 0.5 0.5 8 EG activation energy eV 1.11 1.11 Si 0.69 Sbd 0.67 Ge 9 XTI saturation-current temp. exp - 3.0 3.0 jn 2.0 Sbd 10 KF flicker noise coefficient - 0 11 AF flicker noise exponent - 1 12 FC coefficient for forward-bias - 0.5 depletion capacitance formula 13 BV reverse breakdown voltage V infinite 40.0 14 IBV current at breakdown voltage A 1.0E-3 36 7.14. BJT Models (both NPN and PNP) The bipolar junction transistor model in SPICE is an adapta- tion of the integral charge control model of Gummel and Poon. This modified Gummel-Poon model extends the original model to include several effects at high bias levels. The model will automatically simplify to the simpler Ebers-Moll model when cer- tain parameters are not specified. The parameter names used in the modified Gummel-Poon model have been chosen to be more easily understood by the program user, and to reflect better both physi- cal and circuit design thinking. The dc model is defined by the parameters IS, BF, NF, ISE, IKF, and NE which determine the forward current gain characteris- tics, IS, BR, NR, ISC, IKR, and NC which determine the reverse current gain characteristics, and VAF and VAR which determine the output conductance for forward and reverse regions. Three ohmic resistances RB, RC, and RE are included, where RB can be high current dependent. Base charge storage is modeled by forward and reverse transit times, TF and TR, the forward transit time TF being bias dependent if desired, and nonlinear depletion layer capacitances which are determined by CJE, VJE, and MJE for the B-E junction , CJC, VJC, and MJC for the B-C junction and CJS, VJS, and MJS for the C-S (Collector-Substrate) junction. The temperature dependence of the saturation current, IS, is deter- mined by the energy-gap, EG, and the saturation current tempera- 37 ture exponent, XTI. Additionally base current temperature depen- dence is modeled by the beta temperature exponent XTB in the new model. The BJT parameters used in the modified Gummel-Poon model are listed below. The parameter names used in earlier versions of SPICE2 are still accepted. Modified Gummel-Poon BJT Parameters. name parameter units default example area 1 IS transport saturation current A 1.0E-16 1.0E-15 * 2 BF ideal maximum forward beta - 100 100 3 NF forward current emission coefficient - 1.0 1 4 VAF forward Early voltage V infinite 200 5 IKF corner for forward beta high current roll-off A infinite 0.01 * 6 ISE B-E leakage saturation current A 0 1.0E-13 * 7 NE B-E leakage emission coefficient - 1.5 2 8 BR ideal maximum reverse beta - 1 0.1 9 NR reverse current emission coefficient - 1 1 10 VAR reverse Early voltage V infinite 200 11 IKR corner for reverse beta high current roll-off A infinite 0.01 * 12 ISC B-C leakage saturation current A 0 1.0E-13 * 13 NC B-C leakage emission coefficient - 2 1.5 14 RB zero bias base resistance Ohms 0 100 * 15 IRB current where base resistance falls halfway to its min value A infinite 0.1 * 16 RBM minimum base resistance at high currents Ohms RB 10 * 17 RE emitter resistance Ohms 0 1 * 18 RC collector resistance Ohms 0 10 * 19 CJE B-E zero-bias depletion capacitance F 0 2PF * 20 VJE B-E built-in potential V 0.75 0.6 21 MJE B-E junction exponential factor - 0.33 0.33 22 TF ideal forward transit time sec 0 0.1Ns 23 XTF coefficient for bias dependence of TF - 0 24 VTF voltage describing VBC dependence of TF V infinite 38 25 ITF high-current parameter for effect on TF A 0 * 26 PTF excess phase at freq=1.0/(TF*2PI) Hz deg 0 27 CJC B-C zero-bias depletion capacitance F 0 2PF * 28 VJC B-C built-in potential V 0.75 0.5 29 MJC B-C junction exponential factor - 0.33 0.5 30 XCJC fraction of B-C depletion capacitance - 1 connected to internal base node 31 TR ideal reverse transit time sec 0 10Ns 32 CJS zero-bias collector-substrate capacitance F 0 2PF * 33 VJS substrate junction built-in potential V 0.75 34 MJS substrate junction exponential factor - 0 0.5 35 XTB forward and reverse beta temperature exponent - 0 36 EG energy gap for temperature effect on IS eV 1.11 37 XTI temperature exponent for effect on IS - 3 38 KF flicker-noise coefficient - 0 39 AF flicker-noise exponent - 1 40 FC coefficient for forward-bias depletion capacitance formula - 0.5 7.15. JFET Models (both N and P Channel) The JFET model is derived from the FET model of Shichman and Hodges. The dc characteristics are defined by the parameters VTO and BETA, which determine the variation of drain current with gate voltage, LAMBDA, which determines the output conductance, and IS, the saturation current of the two gate junctions. Two ohmic resistances, RD and RS, are included. Charge storage is modeled by nonlinear depletion layer capacitances for both gate junctions which vary as the -1/2 power of junction voltage and are defined by the parameters CGS, CGD, and PB. name parameter units default example area 1 VTO threshold voltage V -2.0 -2.0 2 BETA transconductance parameter A/V**2 1.0E-4 1.0E-3 * 3 LAMBDA channel length modulation parameter 1/V 0 1.0E-4 4 RD drain ohmic resistance Ohm 0 100 * 5 RS source ohmic resistance Ohm 0 100 * 39 6 CGS zero-bias G-S junction capacitance F 0 5PF * 7 CGD zero-bias G-D junction capacitance F 0 1PF * 8 PB gate junction potential V 1 0.6 9 IS gate junction saturation current A 1.0E-14 1.0E-14 * 10 KF flicker noise coefficient - 0 11 AF flicker noise exponent - 1 12 FC coefficient for forward-bias - 0.5 depletion capacitance formula 7.16. MOSFET Models (both N and P channel) SPICE provides four MOSFET device models, which differ in the formulation of the I-V characteristic. The variable LEVEL specifies the model to be used: LEVEL=1 -> Shichman-Hodges LEVEL=2 -> MOS2 (as described in [1]) LEVEL=3 -> MOS3, a semi-empirical model(see [1]) LEVEL=4 -> BSIM (as described in [2]) The dc characteristics of the level 1 through level 3 MOSFETs are defined by the device parameters VTO, KP, LAMBDA, PHI and GAMMA. These parameters are computed by SPICE if process parameters (NSUB, TOX, ...) are given, but user-specified values always override. VTO is positive (negative) for enhancement mode and negative (positive) for depletion mode N-channel (P-channel) dev- ices. Charge storage is modeled by three constant capacitors, CGSO, CGDO, and CGBO which represent overlap capacitances, by the nonlinear thin-oxide capacitance which is distributed among the gate, source, drain, and bulk regions, and by the nonlinear depletion-layer capacitances for both substrate junctions divided 40 into bottom and periphery, which vary as the MJ and MJSW power of junction voltage respectively, and are determined by the parame- ters CBD, CBS, CJ, CJSW, MJ, MJSW and PB. Charge storage effects are modeled by the piecewise linear voltags-dependent capacitance model proposed by Meyer. The thin-oxide charge storage effects are treated slightly different for the LEVEL=1 model. These voltage-dependent capacitances are included only if TOX is speci- fied in the input description and they are represented using Meyer's formulation. There is some overlap among the parameters describing the junctions, e.g. the reverse current can be input either as IS (in A) or as JS (in A/m**2). Whereas the first is an absolute value the second is multiplied by AD and AS to give the reverse current of the drain and source junctions respectively. This methodology has been chosen since there is no sense in relating always junc- tion characteristics with AD and AS entered on the device card; the areas can be defaulted. The same idea applies also to the zero-bias junction capacitances CBD and CBS (in F) on one hand, and CJ (in F/m**2) on the other. The parasitic drain and source series resistance can be expressed as either RD and RS (in ohms) or RSH (in ohms/sq.), the latter being multiplied by the number of squares NRD and NRS input on the device card. SPICE level 1 to level 3 parameters. name parameter units default example 1 LEVEL model index - 1 2 VTO zero-bias threshold voltage V 0.0 1.0 3 KP transconductance parameter A/V**2 2.0E-5 3.1E-5 4 GAMMA bulk threshold parameter V**0.5 0.0 0.37 5 PHI surface potential V 0.6 0.65 41 6 LAMBDA channel-length modulation (MOS1 and MOS2 only) 1/V 0.0 0.02 7 RD drain ohmic resistance Ohm 0.0 1.0 8 RS source ohmic resistance Ohm 0.0 1.0 9 CBD zero-bias B-D junction capacitance F 0.0 20FF 10 CBS zero-bias B-S junction capacitance F 0.0 20FF 11 IS bulk junction saturation current A 1.0E-14 1.0E-15 12 PB bulk junction potential V 0.8 0.87 13 CGSO gate-source overlap capacitance per meter channel width F/m 0.0 4.0E-11 14 CGDO gate-drain overlap capacitance per meter channel width F/m 0.0 4.0E-11 15 CGBO gate-bulk overlap capacitance per meter channel length F/m 0.0 2.0E-10 16 RSH drain and source diffusion sheet resistance Ohm/sq. 0.0 10.0 17 CJ zero-bias bulk junction bottom cap. per sq-meter of junction area F/m**2 0.0 2.0E-4 18 MJ bulk junction bottom grading coef. - 0.5 0.5 19 CJSW zero-bias bulk junction sidewall cap. per meter of junction perimeter F/m 0.0 1.0E-9 20 MJSW bulk junction sidewall grading coef. - 0.50(level1) 0.33(level2,3) 21 JS bulk junction saturation current per sq-meter of junction area A/m**2 1.0E-8 22 TOX oxide thickness meter 1.0E-7 1.0E-7 23 NSUB substrate doping 1/cm**3 0.0 4.0E15 24 NSS surface state density 1/cm**2 0.0 1.0E10 25 NFS fast surface state density 1/cm**2 0.0 1.0E10 26 TPG type of gate material: - 1.0 +1 opp. to substrate -1 same as substrate 0 Al gate 27 XJ metallurgical junction depth meter 0.0 1U 28 LD lateral diffusion meter 0.0 0.8U 29 UO surface mobility cm**2/V-s 600 700 30 UCRIT critical field for mobility degradation (MOS2 only) V/cm 1.0E4 1.0E4 31 UEXP critical field exponent in mobility degradation (MOS2 only) - 0.0 0.1 32 UTRA transverse field coef (mobility) (deleted for MOS2) - 0.0 0.3 33 VMAX maximum drift velocity of carriers m/s 0.0 5.0E4 34 NEFF total channel charge (fixed and mobile) coefficient (MOS2 only) - 1.0 5.0 35 KF flicker noise coefficient - 0.0 1.0E-26 36 AF flicker noise exponent - 1.0 1.2 37 FC coefficient for forward-bias depletion capacitance formula - 0.5 38 DELTA width effect on threshold voltage (MOS2 and MOS3) - 0.0 1.0 42 39 THETA mobility modulation (MOS3 only) 1/V 0.0 0.1 40 ETA static feedback (MOS3 only) - 0.0 1.0 41 KAPPA saturation field factor (MOS3 only) - 0.2 0.5 The level 4 parameters are all values obtained from process characterization, and can be generated automatically. J. Pierret [3] describes a means of generating a 'process' file, and the program Proc2Mod provided with SPICE3 will convert this file into a sequence of .MODEL cards suitable for inclusion in a SPICE deck. Parameters marked below with an * in the l/w column also have corresponding parameters with a length and width dependency. For example, VFB is the basic parameter with units of Volts, and LVFB and WVFB also exist and have units of Volt-Mmeter The for- mula P P P=P +_____L____+_____W____ 0 L W effective effective is used to evaluate the parameter for the actual device specified with L =L -DL effective input and W =W -DW effective input Note that unlike the other models in SPICE, the BSIM model is designed for use with a process characterization system that provides all the parameters, thus there are no defaults for the 43 parameters, and leaving one out is considered an error. For an example set of parameters and the format of a process file, see the SPICE2 implementation notes[2]. SPICE BSIM (level 4) parameters. name parameter units l/w VFB flat-band voltage V * PHI surface inversion potential V * K1 body effect coefficient V1/2 * K2 drain/source depletion charge sharing coefficient - * ETA zero-bias drain-induced barrier lowering coefficient - * MUZ zero-bias mobility cm2/V-s DL shortening of channel Mm DW narrowing of channel Mm U0 zero-bias transverse-field mobility degradation coefficient V-1 * U1 zero-bias velocity saturation coefficient Mm/V * X2MZ sens. of mobility to substrate bias at v =0 cm2/V2-s * X2E sens. of drain-induced barrier lowering dsfect to substrate bias V-1 * X3E sens. of drain-induced barrier lowering effect to drain bias at V =V V-1 * X2U0 sens. of transverse field mobility degradation effect to substratdsbidd V-2 * X2U1 sens. of velocity saturation effect to substrate bias MmV-2 * MUS mobility at zero substrate bias and at V =V cm2/V2-s X2MS sens. of mobility to substrate bias at Vds=Vdd cm2/V2-s * X3MS sens. of mobility to drain bias at V =Vds dd cm2/V2-s * X3U1 sens. of velocity saturation effect ds dddin bias at V =V MmV-2 * TOX gate oxide thickness ds dd Mm TEMP temperature at which parameters were measured oC VDD measurement bias range V CGDO gate-drain overlap capacitance per meter channel width F/m CGSO gate-source overlap capacitance per meter channel width F/m CGBO gate-bulk overlap capacitance per meter channel length F/m XPART gate-oxide capacitance charge model flag - N0 zero-bias subthreshold slope coefficient - * NB sens. of subthreshold slope to substrate bias - * ND sens. of subthreshold slope to drain bias - * XPART = 0 selects a 40/60 drain/source charge partition in saturation, while XPART=1 selects a 0/100 drain/source charge 44 partition. XPART=1 is recommended. [1] A. Vladimirescu and S. Liu, "The Simulation of MOS Integrated Circuits Using SPICE2", ERL Memo No. ERL M80/7, Electronics Research Laboratory, University of California, Berkeley, Oct. 1980. [2] B. J. Sheu, D. L. Scharfetter, and P. K. Ko, "SPICE2 Imple- mentation of BSIM" ERL Memo No. ERL M85/42, Electronics Research Laboratory, University of California, Berkeley, May 1985. [3] J. R. Pierret, "A MOS Parameter Extraction Program for the BSIM Model" ERL Memo Nos. ERL M84/99 and M84/100, Electronics Research Laboratory, University of California, Berkeley, Nov. 1984. 8. SUBCIRCUITS A subcircuit that consists of SPICE elements can be defined and referenced in a fashion similar to device models. The sub- circuit is defined in the input deck by a grouping of element cards; the program then automatically inserts the group of ele- ments wherever the subcircuit is referenced. There is no limit on the size or complexity of subcircuits, and subcircuits may contain other subcircuits. An example of subcircuit usage is given in Appendix A. 45 8.1. .SUBCKT Card General form: Examples: A circuit definition is begun with a .SUBCKT card. SUBNAM is the subcircuit name, and N1, N2, ... are the external nodes, which cannot be zero. The group of element cards which immedi- ately follow the .SUBCKT card define the subcircuit. The last card in a subcircuit definition is the .ENDS card (see below). Control cards may not appear within a subcircuit definition; however, subcircuit definitions may contain anything else, including other subcircuit definitions, device models, and sub- circuit calls (see below). Note that any device models or sub- circuit definitions included as part of a subcircuit definition are strictly local (i.e., such models and definitions are not known outside the subcircuit definition). Also, any element nodes not included on the .SUBCKT card are strictly local, with the exception of 0 (ground) which is always global. 8.2. .ENDS Card General form: .ENDS <SUBNAM> 46 Examples: .ENDS OPAMP This card must be the last one for any subcircuit defini- tion. The subcircuit name, if included, indicates which subcir- cuit definition is being terminated; if omitted, all subcircuits being defined are terminated. The name is needed only when nested subcircuit definitions are being made. 8.3. Subcircuit Calls General form: XYYYYYYY N1 <N2 N3 ...> SUBNAM Examples: X1 2 4 17 3 1 MULTI Subcircuits are used in SPICE by specifying pseudo-elements beginning with the letter X, followed by the circuit nodes to be used in expanding the subcircuit. 47 9. CONTROL CARDS 9.1. .OPTIONS Card General form: .OPTIONS OPT1 OPT2 ... (or OPT=OPTVAL ...) Examples: .OPTIONS RELTOL=.005 TRTOL=8 This card allows the user to reset program control and user options for specific simulation purposes. Any combination of the following options may be included, in any order. 'x' (below) represents some positive number. option effect GMIN=x resets the value of GMIN, the minimum conductance allowed by the program. The default value is 1.0E-12. RELTOL=x resets the relative error tolerance of the program. The default value is 0.001 (0.1 percent). ABSTOL=x resets the absolute current error tolerance of the program. The default value is 1 picoamp. VNTOL=x resets the absolute voltage error tolerance of the program. The default value is 1 microvolt. TRTOL=x resets the transient error tolerance. The default value is 7.0. This parameter is an estimate of the factor by which SPICE overestimates the actual truncation error. CHGTOL=x resets the charge tolerance of the program. The default value is 1.0E-14. PIVTOL=x resets the absolute minimum value for a matrix entry to be accepted as a pivot. The default value is 1.0E-13. PIVREL=x resets the relative ratio between the largest column entry and an acceptable pivot value. The default value is 1.0E-3. In the numerical pivoting algorithm the allowed minimum 48 pivot value is determined by EPSREL=AMAX1(PIVREL*MAXVAL,PIVTOL) where MAXVAL is the maximum element in the column where a pivot is sought (partial pivoting). TNOM=x resets the nominal temperature. The default value is 27 deg C (300 deg K). ITL1=x resets the dc iteration limit. The default is 100. ITL2=x resets the dc transfer curve iteration limit. The default is 50. ITL5=x resets the transient analysis total iteration limit. the default is 5000. Set ITL5=0 to omit this test. DEFL=x resets the value for MOS channel length; the default is 100.0 micrometer. DEFW=x resets the value for MOS channel width; the default is 100.0 micrometer. DEFAD=x resets the value for MOS drain diffusion area; the default is 0.0. DEFAS=x resets the value for MOS source diffusion area; the default is 0.0. 9.2. .OP Card General form: .OP The inclusion of this card in an input deck will force SPICE to determine the dc operating point of the circuit with inductors shorted and capacitors opened. Note: a dc analysis is automati- cally performed prior to a transient analysis to determine the transient initial conditions, and prior to an ac small-signal analysis to determine the linearized, small-signal models for nonlinear devices. 49 SPICE performs a dc operating point analysis if no other analyses are requested. 9.3. .DC Card General form: .DC SRCNAM VSTART VSTOP VINCR [SRC2 START2 STOP2 INCR2] Examples: .DC VIN 0.25 5.0 0.25 .DC VDS 0 10 .5 VGS 0 5 1 .DC VCE 0 10 .25 IB 0 10U 1U This card defines the dc transfer curve source and sweep limits. SRCNAM is the name of an independent voltage or current source. VSTART, VSTOP, and VINCR are the starting, final, and incrementing values respectively. The first example will cause the value of the voltage source VIN to be swept from 0.25 Volts to 5.0 Volts in increments of 0.25 Volts. A second source (SRC2) may optionally be specified with associated sweep parameters. In this case, the first source will be swept over its range for each value of the second source. This option can be useful for obtaining semiconductor device output characteristics. See the second example data deck in that section of the guide. 50 9.4. .NODESET Card General form: .NODESET V(NODNUM)=VAL V(NODNUM)=VAL ... Examples: .NODESET V(12)=4.5 V(4)=2.23 This card helps the program find the dc or initial transient solution by making a preliminary pass with the specified nodes held to the given voltages. The restriction is then released and the iteration continues to the true solution. The .NODESET card may be necessary for convergence on bistable or astable circuits. In general, this card should not be necessary. 9.5. .IC Card General form: .IC V(NODNUM)=VAL V(NODNUM)=VAL ... Examples: .IC V(11)=5 V(4)=-5 V(2)=2.2 This card is for setting transient initial conditions. It has two different interpretations, depending on whether the UIC parameter is specified on the .TRAN card. Also, one should not 51 confuse this card with the .NODESET card. The .NODESET card is only to help dc convergence, and does not affect final bias solu- tion (except for multi-stable circuits). The two interpretations of this card are as follows: 1. When the UIC parameter is specified on the .TRAN card, then the node voltages specified on the .IC card are used to compute the capacitor, diode, BJT, JFET, and MOSFET initial conditions. This is equivalent to specifying the IC=... parameter on each device card, but is much more convenient. The IC=... parameter can still be specified and will take precedence over the .IC values. Since no dc bias (initial transient) solution is com- puted before the transient analysis, one should take care to specify all dc source voltages on the .IC card if they are to be used to compute device initial conditions. 2. When the UIC parameter is not specified on the .TRAN card, the dc bias (initial transient) solution will be computed before the transient analysis. In this case, the node voltages speci- fied on the .IC card will be forced to the desired initial values during the bias solution. During transient analysis, the con- straint on these node voltages is removed. 9.6. .AC Card General form: .AC DEC ND FSTART FSTOP 52 .AC OCT NO FSTART FSTOP .AC LIN NP FSTART FSTOP Examples: .AC DEC 10 1 10K .AC DEC 10 1K 100MEG .AC LIN 100 1 100HZ DEC stands for decade variation, and ND is the number of points per decade. OCT stands for octave variation, and NO is the number of points per octave. LIN stands for linear varia- tion, and NP is the number of points. FSTART is the starting frequency, and FSTOP is the final frequency. If this card is included in the deck, SPICE will perform an ac analysis of the circuit over the specified frequency range. Note that in order for this analysis to be meaningful, at least one independent source must have been specified with an ac value. 9.7. .TRAN Card General form: .TRAN TSTEP TSTOP <TSTART <TMAX>> Examples: .TRAN 1NS 100NS .TRAN 1NS 1000NS 500NS .TRAN 10NS 1US 53 TSTEP is the printing or plotting increment for line-printer output. For use with the post-processor, TSTEP is the suggested computing increment. TSTOP is the final time, and TSTART is the initial time. If TSTART is omitted, it is assumed to be zero. The transient analysis always begins at time zero. In the inter- val <zero, TSTART>, the circuit is analyzed (to reach a steady state), but no outputs are stored. In the interval <TSTART, TSTOP>, the circuit is analyzed and outputs are stored. TMAX is the maximum stepsize that SPICE will use (for default, the pro- gram chooses either TSTEP or (TSTOP-TSTART)/50.0, whichever is smaller. TMAX is useful when one wishes to guarantee a computing interval which is smaller than the printer increment, TSTEP. UIC (use initial conditions) is an optional keyword which indicates that the user does not want SPICE to solve for the quiescent operating point before beginning the transient analysis. If this keyword is specified, SPICE uses the values specified using IC=... on the various elements as the initial transient condition and proceeds with the analysis. If the .IC card has been specified, then the node voltages on the .IC card are used to compute the intitial conditions for the devices. Look at the description on the .IC card for its interpretation when UIC is not specified. 54 9.8. .FOUR Card The .FOUR card used by SPICE2 to request fourier analysis of outputs has been replaced by the fourier command in nutmeg and the interactive SPICE3 front end. For details of this command, see the manuals for these interfaces. 10. APPENDIX A: EXAMPLE DATA DECKS 10.1. Circuit 1 The following deck determines the dc operating point of a simple differential pair. In addition, the ac small-signal response is computed over the frequency range 1Hz to 100MEGHz. SIMPLE DIFFERENTIAL PAIR VCC 7 0 12 VEE 8 0 -12 VIN 1 0 AC 1 RS1 1 2 1K RS2 6 0 1K Q1 3 2 4 MOD1 Q2 5 6 4 MOD1 RC1 7 3 10K RC2 7 5 10K RE 4 8 10K .MODEL MOD1 NPN BF=50 VAF=50 IS=1.E-12 RB=100 CJC=.5PF TF=.6NS .AC DEC 10 1 100MEG .END 55 10.2. Circuit 2 The following deck computes the output characteristics of a MOS- FET device over the range 0-10V for VDS and 0-5V for VGS. MOS OUTPUT CHARACTERISTICS .OPTIONS NODE NOPAGE VDS 3 0 VGS 2 0 M1 1 2 0 0 MOD1 L=4U W=6U AD=10P AS=10P .MODEL MOD1 NMOS VTO=-2 NSUB=1.0E15 UO=550 * VIDS MEASURES ID, WE COULD HAVE USED VDS, BUT ID WOULD BE NEGATIVE VIDS 3 1 .DC VDS 0 10 .5 VGS 0 5 1 .END 10.3. Circuit 3 The following deck determines the dc transfer curve and the transient pulse response of a simple RTL inverter. The input is a pulse from 0 to 5 Volts with delay, rise, and fall times of 2ns and a pulse width of 30ns. The transient interval is 0 to 100ns, with printing to be done every nanosecond. SIMPLE RTL INVERTER VCC 4 0 5 VIN 1 0 PULSE 0 5 2NS 2NS 2NS 30NS RB 1 2 10K Q1 3 2 0 Q1 RC 3 4 1K .MODEL Q1 NPN BF 20 RB 100 TF .1NS CJC 2PF .DC VIN 0 5 0.1 .TRAN 1NS 100NS .END 56 10.4. Circuit 4 The following deck simulates a four-bit binary adder, using several subcircuits to describe various pieces of the overall circuit. ADDER - 4 BIT ALL-NAND-GATE BINARY ADDER *** SUBCIRCUIT DEFINITIONS .SUBCKT NAND 1 2 3 4 * NODES: INPUT(2), OUTPUT, VCC Q1 9 5 1 QMOD D1CLAMP 0 1 DMOD Q2 9 5 2 QMOD D2CLAMP 0 2 DMOD RB 4 5 4K R1 4 6 1.6K Q3 6 9 8 QMOD R2 8 0 1K RC 4 7 130 Q4 7 6 10 QMOD DVBEDROP 10 3 DMOD Q5 3 8 0 QMOD .ENDS NAND .SUBCKT ONEBIT 1 2 3 4 5 6 * NODES: INPUT(2), CARRY-IN, OUTPUT, CARRY-OUT, VCC X1 1 2 7 6 NAND X2 1 7 8 6 NAND X3 2 7 9 6 NAND X4 8 9 10 6 NAND X5 3 10 11 6 NAND X6 3 11 12 6 NAND X7 10 11 13 6 NAND X8 12 13 4 6 NAND X9 11 7 5 6 NAND .ENDS ONEBIT .SUBCKT TWOBIT 1 2 3 4 5 6 7 8 9 * NODES: INPUT - BIT0(2) / BIT1(2), OUTPUT - BIT0 / BIT1, * CARRY-IN, CARRY-OUT, VCC X1 1 2 7 5 10 9 ONEBIT X2 3 4 10 6 8 9 ONEBIT .ENDS TWOBIT .SUBCKT FOURBIT 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 57 * NODES: INPUT - BIT0(2) / BIT1(2) / BIT2(2) / BIT3(2), * OUTPUT - BIT0 / BIT1 / BIT2 / BIT3, CARRY-IN, CARRY-OUT, VCC X1 1 2 3 4 9 10 13 16 15 TWOBIT X2 5 6 7 8 11 12 16 14 15 TWOBIT .ENDS FOURBIT *** DEFINE NOMINAL CIRCUIT .MODEL DMOD D .MODEL QMOD NPN(BF=75 RB=100 CJE=1PF CJC=3PF) VCC 99 0 DC 5V VIN1A 1 0 PULSE(0 3 0 10NS 10NS 10NS 50NS) VIN1B 2 0 PULSE(0 3 0 10NS 10NS 20NS 100NS) VIN2A 3 0 PULSE(0 3 0 10NS 10NS 40NS 200NS) VIN2B 4 0 PULSE(0 3 0 10NS 10NS 80NS 400NS) VIN3A 5 0 PULSE(0 3 0 10NS 10NS 160NS 800NS) VIN3B 6 0 PULSE(0 3 0 10NS 10NS 320NS 1600NS) VIN4A 7 0 PULSE(0 3 0 10NS 10NS 640NS 3200NS) VIN4B 8 0 PULSE(0 3 0 10NS 10NS 1280NS 6400NS) X1 1 2 3 4 5 6 7 8 9 10 11 12 0 13 99 FOURBIT RBIT0 9 0 1K RBIT1 10 0 1K RBIT2 11 0 1K RBIT3 12 0 1K RCOUT 13 0 1K *** (FOR THOSE WITH MONEY (AND MEMORY) TO BURN) .TRAN 1NS 6400NS .END 10.5. Circuit 5 The following deck simulates a transmission-line inverter. Two transmission-line elements are required since two propagation modes are excited. In the case of a coaxial line, the first line (T1) models the inner conductor with respect to the shield, and the second line (T2) models the shield with respect to the out- side world. 58 TRANSMISSION-LINE INVERTER V1 1 0 PULSE(0 1 0 0.1N) R1 1 2 50 X1 2 0 0 4 TLINE R2 4 0 50 .SUBCKT TLINE 1 2 3 4 T1 1 2 3 4 Z0=50 TD=1.5NS T2 2 0 4 0 Z0=100 TD=1NS .ENDS TLINE .TRAN 0.1NS 20NS .END