Introduction to LTSpice

Transcription

1 Usage of Introduction to Department of EECS Jacobs University Bremen Instructors - Dr. Mathias Bode and - - m.bode@jacobs-university.de tel.: u.pagel@jacobs-university.de tel.: Website -

2 Outline Usage of Usage of

3 Design Flow Why Simulation? Simulators Usage of The normal design flow is: Develop a circuit (on paper) Check the design Improve the design Iterate through check/ improve Build/ use the developed circuit Design flow Checking a design means building a circuit, determine and improving the properties. This might be a time consuming process so in the early 1970s people at Berkeley started to develop a simulation program called SPICE. Simulation Program with Integrated Circuit Emphasis

4 Design Flow Why Simulation? Simulators Usage of Why should we use a simulation software? Why Simulation? The simulator allows a designer to evaluate a (maybe huge) circuit without building it. It makes it simple to check variations of a design It is possible to vary tolerances of components and the environment (temperature) It saves time and money After simulating a design the developer knows what to expect when building the circuit. Simulation alone is not sufficient to check the function of a circuit!!. The final hardware setup may add additional effects!

5 Design Flow Why Simulation? Simulators Simulators Usage of There are different specialized simulators available: for Analog circuits for pure digital circuits for mixed analog and digital circuits Of course digital circuits consist of analog elements. So in general it is possible to use an analog simulator. For optimization reasons these programs work different than the analog simulators.

6 From SPICE to LTSPice How works Usage of What is available - what will we use in lab: From SPICE to LTSPice As already mentioned in the beginning the development of SPICE started in the early 1970s at Berkeley. The last public domain version was SPICE3 in the mid 1980s. Based on the last Spice version commercial simulators were developed. These simulators cover printed circuit board design or integrated circuit design. Commercial simulators are in the range of several keur. Free trial versions are highly limited. In the lab we use one of the rare free (highly used) simulators developed and released from Linear Technology. This simulator is not limited in function. It is based on the old Spice and fully compatible. Of course you should use their components and libraries but it is no problem to use models and libraries from other sources.

7 From SPICE to LTSPice How works Usage of How works How works Spice works the same way how one would do it on paper! It will do a nodal analysis of the circuit, generate the equations and solve the resulting matrixes. Non-linear elements like diodes or transistors will be replaced by a simplified equivalent circuit before doing the nodal analysis. Example : Transistor p-model

8 From SPICE to LTSPice How works Usage of Circuit Elements Special functions How works - Axx - n1 n2 n3 n4 n5 n6 n7 n8 + <model> [extra parameters] Arbitrary behavioral source - Bxx - n+ n- <V=... or I=...> Capacitor - Cxx - n+ n- <capacitance> + [ic=<val.>] [Rser=<val.>] + [Lser=<val.>] [Rpar=<val.>] + [Cpar=<val.>] [m=<val.>] Diode - Dxx A K <model> [area] Voltage dependent voltage - Exx - n+ n- nc+ nc- <gain> Current dependent current - Fxx - n+ n- <Vnam> <gain> Voltage dependent current - Gxx - n+ n- nc+ nc- <transcond.> Current dependent voltage - Hxx - n+ n- <Vnam> <transres.> Independent current source - Ixx - n+ n- <current> JFET transistor - Jxx - D G S <model> [area] [off] + [IC=<Vds,Vgs>] [temp=<t>] Mutual inductance - Kxx - L1 L2 L3... <coeff.> Inductance - Lxx - n+ n- <inductance>[ic=<val.>] + [Rser=<val.>] [Rpar=<val.>] + [Cpar=<val.>] [m=<val.>]

9 From SPICE to LTSPice How works Usage of Circuit Elements MOSFET transistor Lossy transmission line Bipolar transistor Resistor Voltage controlled switch Lossless transmission line Uniform RC-line How works - Mxx - D G S B <model> [L=<len>] + [W=<width>] [AD=<area>] + [AS=<area>] [PD=<perim>] + [PS=<perim>] [NRD=<value>] + [NRS=<value>] [off] + [IC=<Vds, Vgs, Vbs> + [temp=<t>] - Oxx - L+ L- R+ R- <model> - Qxx - C B E [S] <model> [area] + [off] [IC=Vbe,Vce][temp=<T>] - Rxx - n1 n2 <value> - Sxx - n1 n2 nc+ nc- <model> [on,off] - Txx - L+ L- R+ R- ZO=<value> TD=<value> - Uxx - n1 n2 ncommon <model> L=<len> + [N=<lumps>] Independent voltage source - Vxx - n+ n- <voltage> Current controlled switch - Wxx - n1 n2 <Vnam> <model> [on,off] Subcircuit - Xxx - n1 n2 n3... <subckt name> MESFET transistor - Zxx - D G S model [area] [off] [IC=<Vds,Vgs>]

10 How works From SPICE to LTSPice How works Usage of Circuit Elements Circuit elements... are the generic components of a Spice simulation. describe the outline and the behavior of an element. are in almost all cases already some kind of model because there is no element which is pure. might be custom designed using Special Function and Subcircuit. All basic elements are predefined with basic models and meaningful parameters. So it is possible to simulate a circuit in any case. A real simulation needs adjusted models usually provided by the manufacturer of an element.

11 From SPICE to LTSPice How works Usage of Net List The net list is the main control of a Spice simulation. How works It is created either with a text editor or it is compiled from a schematic. The net list includes the circuit with all connections and elements, models, sub circuits, and simulation (dot) commands. Example:

12 How works From SPICE to LTSPice How works Usage of Simulation Modes: DC bias point details (.op) DC analysis (.DC <srcnam> <Vstart> <Vstop> <Vincr> + [<srcnam2> <Vstart2> <Vstop2> <Vincr2>] ) Transient analysis.tran <Tstep> <Tstop> [Tstart [dtmax]] [modifiers] AC analysis.ac <oct, dec, lin> <Nsteps> <StartFreq> <EndFreq> Temperature analysis Monte Carlo analysis (Analysis use random parameters)

13 Usage of Circuit input Usage of Circuit input Simulation Output Install Circuit input The archaic way... Use a sketch of the circuit, mark all nodes, and write the net list using a text editor. Add all needed libraries, definitions, and measurement and simulation commands. Store it as a "*.cir" file. Run the simulation! In pre GUI times the only way. Nowadays still reasonable when creating model definitions or special functions. That s why it is necessary to at least understand the contents of a netlist!!!! The usual way today (and in )... Draw the circuit using a schematic editor. Select all needed libraries, definitions, and measurement and simulation commands either from a menu or add it in textual form to the sketch. Save and run the simulation!

14 Usage of Simulation Usage of Circuit input Simulation Output Install Simulation There is not much to say... simply start the simulation by pushing the button!!! In case of problems like missing values, definitions, or connections a window will pop up and will give you a more or less reasonable hint. You will find the text also in the "*.log" file. If the run was successful only in case of a.op simulation a window will pop up. in all other cases the (empty) diagram window will show up. Additional information is written into the "*.log" file. In case of a.op run also the values are shown there.

15 Usage of Circuit input Simulation Output Install Output Usage of Output In prehistoric times... The output is a may be several 1000 lines long list with the requested numbers in several rows! Your problem to make a diagram out of it... Nowadays textual output is only used for special single measurement, e.g. the calculated frequency parameters of a filter, or the DC operation points from an.op analysis. These parameters will show up in the "*.log" file after the simulation run. The usual way today (and in )... After the simulation a diagram screen will show up. Like with a probe on the bread board you point with the cursor to the nodes in the circuit diagram. The time response will be shown in the diagram!! In case of the.op analysis the cursor makes the potential and/or current at that point visible. If needed the value list is still available. This may be used to transfer the values to e.g. MatLab for further analysis.

16 Usage of Circuit input Simulation Output Install Usage of is NOT Case sensitive!!. E.g. the engineering multiplier "milli" can be expressed as "m" or "M". After the component identifier e.g. Q for a BJT the name may have any length and must be unique for every component. When writing a net list or drawing a schematic... You -MUST- define a ground node. There must be a node 0 in the "*.cir" file or the GND symbols has to be placed in the schematic. The ground node is the reference for the simulation!! For the simulation in general... Keep in mind that it is some kind of ideal!! The components might be close to reality but the real hardware may contain some extra elements like line resistance, parasitic inductance and capacitance. The output values are measured with ideal instruments.

17 Usage of Circuit input Simulation Output Install Usage of Numbers can be expressed in scientific notation; e.g., 1e3, in normal format 1000; but can also use engineering multipliers like m, k. So may be written as 1K. Below is a table of understood multipliers: Suffix Multiplier T, t G, g 10 9 Meg, meg 10 6 k. K 10 3 Mil, mil m, M 10 3 u(or µ) 1 6 n, N 10 9 p, P f, F 10 15!!Be careful... "m" or "M" is the same, means "milli". "M" is not "Mega". Use "Meg" instead!!

18 Usage of Install Usage of Circuit input Simulation Output Install Install Download LTspice from The program is named LTspice. It is available as Windows and OSx version! There is no special Linux version. It should work using "Wine". Install LTspice with the suggested options. Although the simulator includes a lot of elements in it s libraries some components for the course are missing. Download the following files from the course web site: AdvEE_Components.zip An analog library with all necessary components. DigLibs.zip A digital circuit library. Instructions how to install the libraries are included in the.zip files! Installation of the software is the prelab this time. The first session in lab is a tutorial on using the simulator!