Intro Mentor

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Introduction in DA and Accusim

names e.g. ~/designs/rc_tp (RC lowpass filter). Do not move this directory.2. the mentor environment files are written for use in the C-shell. The shell is invoked

by typing in the UNIX command: csh .3. your Mentor environment is located in the directory ~/mgc.

Under your home directory you will find two directories, mgc and designs, and some files.The meenings are given below in the table:

mgc/mgc_location_map library pathes for the Mentor tools

mgc/startup startup directory for Design Manager

designs Location of your designs

If an error message appears after typing in a Mentor command that says: "sh: dmgr: notfound", make sure that you are currently working under a C-shell.

Now, the preparation is finished and you can start with the design entry.

3 Schematic Entry

To get familiar with the Mentor tools you will start with the schematic entry of the well

known RC lowpass filter shown in figre 3-1. Resistor R1 has a value of 1k and the

capacitor has a value of 10nF .

figure 3-1: RC Lowpass filter

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Starting from scratch you should first place all the instances before you wire them. Locatethe input ports on the left side of your sheet and the output ports on the right side. A wire isfinished with a double click at the end point. Make sure that there is always a wire betweentwo instances. In Mentor the name of the port is the name of the attached net.

The design entry is typically done within a tools framework. This framework is called'Design Manager' and is shown in figure 3-2.

figure 3-2: Design Manager

From the design manager you can start all the other Mentor tools and modify the designs.The schematic entry is done with the 'Design Architect' (DA) and for the subsequent

simulation you use the analog SPICE simulator 'Accusim II'.

Attention: When you copy or move designs, you should use the Design Manager becausein this case the system will update the references in several design files.

1. Invoke the 'Design Manager' by typing in

dmgr

on the shell of the operating system.

2. Double click 'design_arch' icon in the 'Tools' window and the 'Design Architect'window is generated.

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3. Select 'Open Sheet' from the 'Session Pallette' window. A dialog box will appear.Notice, that you use the 'Open Sheet' button to create a new component but youalso use this button to open an existing component.

4. In the box labelled 'Component Name' complete the path with the name of thecomponent you will be creating (e.g. /user1/bumuellr/designs/rc_tp).

5. Then click 'OK'. For an existing cell, you may use the navigator to locate thecomponent in your directories. Your screen should look like that given in figure 3-3.The menus are context sensitive and therefore the appearance can vary.

figure 3-3: Design Architect with names of regions

6. To enter your schematic, first select analog device library by clicking the left mousebutton in the menu bar:

Libraries -> MGC Analog Libraries -> Display Libraries Palette

The 'MGC Analog Libraries' palette will become visible on the right side of thescreen.

7. You will find the components i.e. the resistor, the capacitor, the portin and theportout, in Generic Parts. Place them in a way given in figure 3-1.

8. To modify the properties of an instance, e.g. the resistor R1, move the cursor overthe resistor and press the left mouse button (LMB). The resistor is highlighted. Nowpress the right mouse button (RMB) and choose:

Properties -> Modify Multiple

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The 'Modify Editable Properties' selection box will appear. Modify the values of thebox to the correspondig values as shown in Fig 3-4. Then click 'OK'.

Fig. 3-4: Modify Editable Properties selection box

The values in this box you have to modify are: INST=R1 and INSTPAR=1k. Forthe other properties use their default values.

9. Switch the palette menu back to 'Schematic' palette by selecting :

Libraries -> Display Schematic Palette

from the main menu bar.10.With the 'Add Wire' button in the schematic palette you can wire the small circuit as

shown in figure 3-1.

11.To name the input and the output ports of the circuit the attached net must benamed.

12.Now, we need to check and save the complete design.

13.To maintain the overview of your desk quit the Design Architect.

Remark: Properties

A property contains additional information about instances that are used by downstreamtools like Accusim. The syntax of a property is

owner property_name value

Accusim e.g. reads the values of the properties INSTPAR and INST of the componentRESISTOR_H and creates the corresponding line in the spice input file.

The colour of the property depends on the owner. The dependencies are given intable 3-1.

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colour owner

yellow net

blue component

magenta pin

Table 3-1: Property Colours

4 Simulation In Accusim

4.1 Create a simulation viewpoint

When you create the schematic using the Design Architect, the DA has no idea what youare going to use the schematic for, digital simulation, analog simulation, VLSI layout, boardlayout, etc. Before the schematic can be used for a specific purpose, a design viewpointmust be created for it. A viewpoint tells the down-stream tool (the tool that uses theschematic after it is created) what information on the schematic is to be used and whatproperties on the instances contain the information. For Accusim we create it using theDesign Viewpoint Editor, DVE.

Open DVE on your rc_tp design from the Design Manager tools window.

Use from the menu bar

Setup -> Accusim

to setup the viewpoint for Accusim.Save the viewpoint with

File- > Save Design viewpoint

and exit DVE.

4.2 Simulate your schematic

1. In the Design Manager tools window, double-click on the "Accusim" icon to invokethe simulator.

2. A dialog box will appear. Enter the complete pathfor the viewpoint of yourschematic you will be simulating.

3. Accusim II window will be open along with your design.

A screenshot of Accusim II window is given in figure 4-1.

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figure 4-1: Accusim Window with RC lowpass filter

4.3 Perform an AC simulation

The frequency response analysis calculates all of the AC node voltages and branchcurrents over a swept range of frequencies. The output of this analysis are the values forthe amplitude of node voltages and device currents.

By frequency response we mean "small-signal frequency response", where the analysis isdone with the assumption that the input signals are small enough to minimize nonlinear

effects.

The input level for the AC source is typically set to 1 volt. Since frequency responseanalysis is a small-signal analysis, this simplifies looking at the ratio of output response toinput excitation.

Before you can start the simulation you must attach a voltage source to your input node.This is done in the following way:

1. Select the input node in the schematic window and click the Add Force button inthe palette.

2. In the Force dialog box, set the Mode to Frequency and the Force Type to AC.

3. Set the Magnitude item to 1 and click OK.

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4. Click the Setup Analysis button in the palette. In the dialog box that comes up, setthe Analysis item to AC. Set the Start Freq item to 1 and the Stop Freq to100Meg. Leave the Sweep Type item set to Decade and click OK.

5. Use the Setup -> Keeps -> Keeps All

6. To start the simulation click the Run button in the palette.

Remember:

SPICE interprets the dimension m or M in e.g. 1MV as 1*10-3 V ( SPICE syntax isnot case sensitive). If you mean the dimension mega you must write MEG or 10E6.

4.4 View the results

Accusim has a powerful waveform postprocessor. The easiest way to view the result of anode is to select this node with the LMB and click from the menu bar

Result -> Chart -> Chart Result

The Chart Result window appears as shown in figure 4-2.

figure 4-2: Chart Result window

Note: The node as selected before will appear in the signal field.

To obtain a bode plot with separated magnitude and the phase response you must choosethis window twice - one with the Mag and the other with the Phase button pressed. Theresult should look like the waveforms in figure 4-3.

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figure 4-3: Bode plot of the RC lowpass filter

Further measurements can be done by using the waveform measurement feature. To getthe passband frequency click from the palette menu

WF Measurement -> Measure Funktion -> lowpass

to obtain the 3dB corner frequency in a text window.

4.5 Perform a Transient simulation

Transient, or time-domain, response simulate the operation of your circuit as timeprogresses and input level change under the control of components values.

Now we will examine how the circuit behaves with a square wave on its input. Close thecurrent Chart window and unselect everything (hit the F2 key). Select the force bubble onthe input node and hit the delete key to remove the force.

To start with the transient analysis select the input node once again and hit the Add Force

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button. In the dialog box set the Mode item to Time and set the Force Type to Pulse.Adjust your dialog box as shown in figure 4.4

figure 4.4: Add Force dialog box

Click on the Setup Analysis button in the palette and set the Analysis item to Transient.Set the Time Step item to 1u and the Stop Time to 1m and click OK.

In the schematic window, select the input and the output nodes and click on the Tracebutton in the palette.

Click on the Run button in the palette to start the simulation. The result should be a tracewindow like the one in figure 4-5.

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figure 4-5: Transient waveforms

Literature

1. Paul W. Tuinenga, SPICE: A Guide to Circuit Simulation & Analyisis USINGPSPICE, ISBN 0138346070, , Prentice Hall, 1988

2. Mildenberger, Otto: "Entwurf analoger und digitaler Filter", 3-528-06430-7, Vieweg,

1st edition, 19923. Best, Roland: "Handbuch der analogen und digitalen Filterungstechnik" 3-85502-

148-1, AT Verlag, 2nd edition, 19874. Sedra/Smith/Roberts: "Spice for Microelectronic Circuit" 0-03-052617-5, Saunders

College Publishing, 3rd edition, 1992

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Appendix

Strokes for Design Architect

12

Intro Mentor

Documents

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