Creating Subcircuits and Hierarchal Blocks in LT Spice
Contents
1. 4 On the schematic include a SPICE Directive with the path of the subcircuit file e g ib C Program Files LTC SwCADIIN My Work OpampExample lib Here is an example of an ideal op amp subcircuit Step 1 Create a subcircuit netlist using a text editor Tdeal Op Amp V V Out subckt myopamp 1 2 3 g1 3021 100Meg ends myopamp means this is a comment This line is for clarity only Subcircuit named myopamp with three pins Dependent source with nodes and gain End of the subcircuit Save As gt OpampExample lib in this example the full path is C Program Files LTC SwCADIIN My Work OpampExample lib f This is what a schematic of the subcircuit would look like g1 is a linear voltage controlled current source with pins of lt node gt lt node gt lt controlling node gt lt controlling node gt lt gain gt Now when the symbol is made the netlist order of the pins will be Inverting Input pin 1 Non Inverting Input pin 2 Output pin 3 Creating Subcircuits and Hierarchical Blocks in LTspice Step 2 The Inverting pin is on top and has a netlist order of 1 The Output is pin 3 Pinl Unnn was created by Edit gt Attributes gt Attribute Window and selecting InstName Pin3 This will appear as U1 U2 etc on the Pin2 schematic Select Edit gt Attributes gt x Ted Attrbutes Add Pin Port p Attribute Window Ctrl w a Move F72. Port Properties dialog box enter the label that matches the schematic oaBlock asc If making a new symbol from scratch use Edit gt Add Pin Port If using a previously created symbol Right Click on the pin to get the Pin Port Properties box Here the pin labels are visible this is optional Creating Subcircuits and Hierarchical Blocks in LTspice Step 3 744 Linear Technology x apalSwtschert AD lll oablock S ele ct Edit gt Attributes gt Edit File Edit Hierarchy Draw View Tools Window Help Po ATH QQQRIIIE Attributes Select Block from the ma symbol Attribute Editor Symbol Type drop down box Leave all attributes blank Save the symbol File gt Save As oaBlock asy Symbol Type Block attribute value Prefix SpiceModel Value VYalue2 SpiceLine SpiceLine2 Description ModelFile Cancel Insert the component in the schematic The displayed name was X1 Change its name if desired by placing the cursor over the label Right Clicking and replacing X1 with op_amp ee Gee 1E BL 16 Notes Right clicking on the component brings up the Navigate Edit Schematic Block dialog box The Symbol or its Schematic can then be opened If the lower level schematic is opened it s symbol can be opened from the Hierarchy menu y Linear Technology LTspice SwitcherCAD III LP_OpAmp asc F 4 Linear Technology LTspice SwitcherCAD III oablock asc File Edit Hierarchy View Simulate Tools Wi
3. hierarchical block a schematic is created to model the op amp and a symbol is made to represent the schematic of the op amp The op amp s schematic is a lower level schematic Selecting the symbol on the higher level schematic allows viewing of the lower level circuitry Once open the voltages and currents can be probed just as in the higher level schematic Procedure 1 Create a schematic of the device to be represented by a block a Use LTspice s schematic capture to draw the circuit If semiconductor models or subcircuits are used add a lib directive with the path and name of the file b Label any nodes that will be connected to the higher level circuit Select Edit gt Label Net In the box next to ABC type a name or number Port Type select None or as desired c Save the schematic as a asc file e g oaBlock asc This can be saved in a working directory Notes on Saving 2 Create a symbol to represent the lower level schematic a Select File gt New Symbol to open the symbol editor b Draw the symbol using the Draw menu and the Line Rect Circle etc commands c Place the pins Select Edit gt Add Pin Port to get the Pin Port Properties dialog box At the top right is the Netlist Order box The Netlist Order is not crucial but the Label box left of the Netlist Order box is very important The Label box must match the Net labels from step 1b To make the label visible select one of the Pin Label Position buttons i
4. lt Drag F8 m EJ AE Delete Duplicate Linear Technology LTspice SwitcherCAD III op_amp_variable asy File Edit Hierarchy Draw View Tools Window Help ascu ye QLA fd BRS sham ASsl ine Eq E Symbol Attribute Editor Symbol Type Cell v This determines the type of a circuit element e g R C or L Prefix x attribute value SSS E Ts SpiceModel Value myopamp Value2 SpiceLine SpiceLine2 Description ModelFile ae Cancel Symbol Type gt Cell Prefix gt X Value gt myopamp The name of the subcircuit myopamp is placed in the Value field This is the name that follows the subckt statement in the netlist not the name of the file File gt Save As gt myopamp asy Creating Subcircuits and Hierarchical Blocks in LTspice Step 4 lib statement tells LTSPICE where to find the file OpampExample lib which contains the subcircuit myopamp lib CAFProgram Filesi LTC SwCADIIMy WorkvOpampExample lib ac dec 100 0 01 10 Notes Right clicking on U1 will bring up the Component Attribute Editor Here information can be made visible on the schematic by selecting the desired line and checking the Visible box Notice an x is shown in the V column indicating the instance name U1 will be visible on the schematic This editor will also allow changes to the attributes listed The path of the device symbol is shown to th
5. Creating Subcircuits and Hierarchical Blocks in LTspice Mike Kelsch January 2007 This tutorial gives some techniques for creating Subcircuits and Hierarchical Blocks using LTspice SwitcherCAD III Version 2 19p available free from Linear Technology at http www linear com company software sp Subcircuits Subcircuits allow the designer to create a model or circuit for a device that may be used many times in a schematic and saved for later use in other circuits Each instance of the device can use the same parameters values or the parameters can be changed on an instance by instance basis The advantage of a subcircuit is that one symbol on a schematic can represent another circuit Whenever that symbol is placed on the schematic the entire subcircuit is placed This allows for ease of design with more clarity on the schematic Procedure 1 Create a netlilst using a text editor such as notepad a use the subckt statement followed by the name of the subcircuit followed by the pins e g subckt myopamp I 2 3 see example The numbers will be used as node numbers for connection to other components 0 is ground The order of the numbers will be the order used for the pin port netlist order on the symbol b End the subcircuit with the ends statement e g ends myopamp c Save the netlist as filename lib or filename sub the name does not have to be the same as the name of the subcircuit in fact more than one
6. Log can be accessed from the View menu and come in handy during troubleshooting A Netlist can be exported as a net file using Tools gt Export Netlist I hope this information is useful To leave comments mk 104mk mindspring com Mike Kelsch Additional information is available from the following LTspice user s manual http Itspice linear com software scad3 pdf LTspice user s group http tech groups yahoo com group LTspice Linear Technology http www linear com 10 Creating Subcircuits and Hierarchical Blocks in LTspice Works Cited Sennewald Helmut 2006 Third Party Models http tech groups yahoo com group LTspice Tront Joseph G 2004 Pspice for Basic Circuit Analysis New York McGraw Hill LTspice Users Manual http Itspice linear com software scad3 pdf Winspice Tutorial 11 Creating Subcircuits and Hierarchical Blocks in LTspice Glossary Device A circuit component This could simply be a resistor or a complex circuit e g an op amp which is represented on the schematic by a symbol Instance each time a component or device is placed on a schematic it is called an instance of that device For example if a circuit contains three Op amps each individual Op amp is an instance of that op amp Each instance is identified by a letter representing the type of component e g R for resistor followed by a unique number Instance numbers can be changed and can contain numbers and or letters as long as n
7. ar Technology LTspice SwitcherCAD III Draft2 asc A directory called MyLib was L File Edit Hierarchy View Simulate Tools Window Help created in the C Pro gram Files LTC SwCADII ib sym directory Closing and restarting Double click to change directory to LI sp ice then op ening the Select MyLib Component Symbol dialog box Edit gt Component shows the directory Double clicking on the directory opens it Save all symbols asy files in this directory and they will now be C Program FilessSLTC SwCADIII lib sym available Each time a new FeriteBead I mestat symbol is saves close and restart nif g2 nmas LTspice nimose curent i npr diode i hpne e npr Be niprid f load pit E Select Component Symbol SpecialFunctions FeriteBead Iprnp pmog bi FeriteBeads ltline prices Si iiil gt Cancel Setting User Preferences Color preferences for background schematic components and text and plots can be changed using the Color Palette Editor Select Tools gt Color Preferences To eliminate the saving of files generated during simulations raw log files etc select Tools gt Control Panel gt Operations Tab and select yes to Automatically Delete Schematic font sizes can be found on the Control Panel gt Drafting Options Tab Also on the Drafting Options Tab is the Hot Keys Button This screen allows for customizing Keyboard shortcuts for commonly performed tasks The SPICE Netlist and Error
8. e right of the Open Symbol button i7 Linear Technology LTspice SwitcherCAD ill LP_OpAmp asc Component Attribute Editor Open Symbol C program fles itc sweadislibyeym mplib smyopamp asy FREM ASL4 P2 390 _LP_OpAmp asc ax This is the name of the instance like a reference designator lnstName ui Visible Attribute Value Prefix k u SpiceModel Value myopamp Value SpiceLine SpiceLinez Jib CAP regram Files LTC Sw ADI My Workpampexample lib ac dec 100 0 01 10 Selecting the Open Symbol button opens the symbol for the device With the symbol opened the Edit gt Attributes commands can be used in the same manner described in steps 2d and 3 Creating Subcircuits and Hierarchical Blocks in LTspice F j Linear Technology LTspice SwitcherCAD III myopamp asy The open symbol can be edited using the File Edit Hierarchy Draw View Tools Window Help eae EEN sew yae Edit gt Attributes commands i LP_OpAmp asc gt myopamp asy E Hierarchical Blocks Creating Hierarchical Blocks is similar to using a subcircuit in that a symbol can represent another circuit in a schematic The hierarchical block is a schematic that is represented on a higher level schematic by a symbol In the example on subcircuits a netlist represented an op amp then a symbol representing that subcircuit was placed on the schematic For a
9. f desired d Some information such as Instance Name can be added by selecting Edit gt Attributes gt Attribute Window and selecting the information Clicking OK will allow pasting on the symbol Creating Subcircuits and Hierarchical Blocks in LTspice 3 Open the Symbol Attribute Editor Select Edit gt Attributes gt Edit Attributes Select Block from the Symbol Type drop down box Leave all attributes blank Save the symbol File gt Save As saves the file as a asy See Notes on Saving 4 Now the component can be placed in a new schematic Here is an example of an ideal op amp using a hierarchical block Step 1 Step 2 F 4 Linear Technology LTspice SwitcherCAD III myopamp asy File Edit Hierarchy Draw View Tools Window Help ASE PT 49 QLQQ Ss BSW sa myopamp asy SEE File Edit Hierarchy Draw View Tools Window Help Aas AP ZARLAR ESRB amp Bw Label Netlist Order Pin Label Position O TOP LEFT RIGHTO BOTTOM O NONE Not Visible C Vertical Text Offset 66 99 Schematic created using g from the symbol library using the Select Component Symbol dialog box Edit gt Component Nodes Labeled using Edit gt Label Net Numbers or names can be used File gt Save As oaBlock asc A new symbol can be created or a previously created symbol can be used Here myopamp asy from the previous example is used In the Label box of the Pin
10. list Options aad Waveforms When not using default models eee a model statement must be El Reverse comp order included on the schematic with es the path and name of the Default Devices model file e g lib C Program Files LTC SwCADIII My Setting remembered between program invocations Work CMOS lib C Default Libraries Notes on Saving LTspice searches for the needed files as specified in the lib or include statement that is placed on the schematic or in a netlist If no statement exists LTspice looks in the SwCDIi ib cmp SwCDIMib sub or the path of the schematic It is recommended to always use the lib or include directive to avoid error messages Here are a couple of techniques that might avoid headaches later 1 Make a working directory in the SwCADIII folder e g C Program Files LTC SwCADII My Work Save all your schematics in this directory 2 Make a directory in the C Program Files LTC SwCADIIMib sym directory to save all newly created symbols This allows selection of a device from the Select Component Symbol dialog box by locating the directory and selecting from the list Now custom components can be kept separately from Linear Technology s library of symbols Creating a directory called MyLib C Program Files LTC SwCADII ib sym MyLib is shown Double clicking on MyLib opens the new directory and lists the available symbols Creating Subcircuits and Hierarchical Blocks in LTspice F j Line
11. ndow Help File Edit Hierarchy View Simulate Tools Window Help Bs UP 409 QOQR BO Bae sae as EE D gt Create a New Symbol K LPO HK Create a New Sheet oablock asc Instance op_amp SEE E Navigate Edit Schematic Block C program files ltc sweadii lib sym mylib oablock asy C Program FilesS LTC SwCADIIISMy Work oablock asc Visible Instance Name PARAMS C Cancel 100meg Creating Subcircuits and Hierarchical Blocks in LTspice Passing Parameters Curley Brackets and the param statement can be used to pass parameters to components Curley brackets enable the use of variables The param statement can be used to specify values for the variables For example Linear Technology LTspice SwitcherCAD III LP_OpAmp asc subckt V_opamp 1 2 3 File Edit Hierarchy View Simulate Tools Window Help _ ASU PF Q0QX BU BBY sham aay 1050 Rout co 3 0 Cout el 3012 Ao _param Cout 1 2 pi fo Rout _param Ao A ends V_opamp E Component Attribute Editor Open Symbol C program files Itc sweadiilib sym mylib op_amp_variable as Attribute Prefix x InstN ame u1 x SpiceModel Value Y_ opamp Value2 SpiceLine 4 100meg fo 10k Rout 10 SpiceLine2 Cancel lib C Program Files LTC SwCADIII My Work opamps lib ac dec 100 0 01 10 Here variables are set using a combination of curly brackets and param statements This allows the
12. o two instances have the same label Instances can have different parameters values Netlist A text file representing a circuit LT Spice recognizes files ending in cir net and sp as netlists The first line of a netlist is taken to be a comment so begin all netlists with a comment End a netlist with the end statement WinSPICE uses filename cir and PSPICE uses filename net Parameters Values for a device or used for calculating the values for the device Parameters can be assigned by use of a param statement or by use of curly brackets in a subcircuit SPICE Directive A command telling a SPICE program to perform an operation SPICE directives can be included in netlists as for a subcircuit or placed on the schematic These directives begin with a period Some examples lib include subckt model tran Place a SPICE directive using Edit gt SPICE Directive or use the op icon Symbol A user created drawing used to represent a device The device could be described by a subcircuit or a hierarchical block To make a symbol select File gt New Symbol Then use the Draw menu to add shapes and text The shapes have no electrical connection The electrical connection is established by placing pin ports using the Edit gt Add Pin Port command
13. subcircuit can be included in a lib or sub file See Notes on Saving 2 Draw a symbol to represent the device a Select File gt New Symbol to open the Symbol Editor b Draw the symbol using the Draw menu and the Line Rect Circle etc commands c Place the pins Select Edit gt Add Pin Port to get the Pin Port Properties dialog box At the top right is the Netlist Order box This order corresponds to the order of the pins in the subciruit A label can be inserted using the Label box e g Vin but has nothing to do with the function of the pin The pin s function relates to the connection specified in the subcircuit netlist To make the label visible select one of the Pin Label Position buttons d Some information such as Instance Name can be added by selecting Edit gt Attributes gt Attribute Window and selecting the information Clicking OK will allow pasting on the symbol Creating Subcircuits and Hierarchical Blocks in LTspice 3 Open the Symbol Attribute Editor to enter the appropriate information a Select Edit gt Attributes gt Edit Attributes 1 Select Cell in the Symbol Type drop down box 11 Select Prefix type X in the Prefix box X tells LTspice that this is a subcircuit 111 In the Value field type the name of the subckt e g myopamp iv SPICELine can be used to pass parameters v Leave ModelFile blank b Save the symbol File gt Save As saves the file as a asy See Notes on Saving
14. use of one subcircuit with parameters being changed on the schematic using the Component Attribute Editor instead of in the netlist Right Clicking the component can access the editor To use this method add the variable names and values to the SpiceLine and SpiceLine2 values e g A 100meg when first creating a symbol see number 3 of the subcircuit procedure Alternatively for an existing symbol use the Component Attribute Editor Each instance of a component can have different parameters through use of the Component Attribute Editor A param statement can also be placed on a schematic as a SPICE Directive Model Statements Some devices such as transistors and diodes require information on the device in order to make calculations A model statement tells LTspice what parameters to use for modeling semiconductors However LTspice uses default models even if a model file is included To use models other than the default select Tools gt Control Panel gt Netlist Options tab and uncheck the Semiconductor Models boxes Remember to use a lib or include directive to include the path of the model file e g lib C Program Files LTC SwCADIII My Work CMOS 1ib Creating Subcircuits and Hierarchical Blocks in LTspice 4 File Edit Hierarchy View Simulate Tools Window Help Sereas A e ASSL Models boxes when not using LTspice default models Compression S Save Defaults F gt SPICE SF Drafting Options Operation Hacks Y Intemet Net
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