Exercise 1
Getting Started with the Cadence Software. Main
Analyses
I.
Getting Started with the Cadence Software.
Schematic Capture
CADENCE DESIGN FRAMEWORK II requires X-windows
(CDE/Openwindows on Sun SPARC stations). It is a common interface to
the complete range of Cadence IC design tools. Using a common database
and user interface, the framework allows easy cross-checking between the
various stages of the design flow, e.g. comparing the layout and the
schematic.
1. Loading Cadence
The first step after loading an UNIX terminal is to create directory where you
will work with Cadence and will save all the schematic and simulation data.
1) mkdir <directory name>
For example: mkdir cadence
The next step is to enter on that directory:
2) cd <directory name>
For example: cd cadence
3) Cadence loading
source ~radonov/scripts/.cshrc-cad446
ams_cds –tech csx –mode fb
The option “–tech cs” determines the technology which parameters will be
used in the design process with Cadence. Now we use “csx” for AMS
technology. Use this option when you start Cadence for
your first time. Use option “-mode fb” to load all necessary libraries for
layout design.
Few seconds after loading Cadence you will see two kinds of windows:
 *CIW – Command Interpreter Window (fig.1)
 *LMW – Library Manager Window (fig.2)
2. The CIW
The Command Interpreter Window, is the Cadence console, it is the first
window that is created, and controls all of the functions which are session
wide.
 Window name - shows the name of the corresponding cadence tool
as well as the full name of the log file where all of the current
sessions are saved.
 Menu bar contains command menus for access to all
CADENCE DESIGN FRAMEWORK II products.
 Log Messages - shows the current session commands and their
results.
 Command entry – enter SKILL commands, which are the Cadence
scripting language.
 Mouse Map – describes the current properties of the mouse
buttons.
 Prompt Line – hints the next step for the current command
3. The LMW
LMW is the cadence library editor which visualizes all created libraries.
With its help it is possible to create, edit or delete libraries, to manipulate
with cells and their cellviews.
The cell is the common name of a project. A library may contain more
than one cell (projects). Each cell may have more than one cellview:
schematic, symbolic, layout, e.g.
4. Creating a Library
In order to create new projects, it is necessary to have a library where to keep
them. To do this, go to menu File of the library browser and choose
command New -> Library, as shown below:
A window “New Library” appears. In New Design Library box type the
new library name, for example: exercise 1 and press OK. The next window
you will see is for attaching the new library to a technology file (Technology
File for New Library). The menu bar allows attaching the new library with
different kinds of technological files. The attaching is with an extant
technological file (Attach to an existing techfile). In the form shown below
(Attach Design Library to Technology File) choose file for 0.35
CMOS, TECH_CSI technology.
5. Creating a new cell (project)
In order to create a new cell from menu File in LMW, choose New ->
CellView. In the opened form for example type:
Library Name: exercise 1
Cell Name
: amplify
View Name : schematic
6. Schematic Capture
In order to create a schematic it is necessary to add and place the
corresponding elements in the Cadence schematic tool (Virtuoso
Schematic Composer). To do this, go to command Add  Instance. A
new dialog window is opened. From Browse button you can choose a
library PRIMLIB (AMS 0.35
), which contains the actual
elements for the used technology. The ideal ones you can find in library
analogLib.
Library  AnalogLib
Cell Name  vdc
View Name  symbol
The chosen element can be placed multiple times in the schematic tool. In order
to cancel the command press Esc. If you change the name of the element in the
Add Instance form you can keep placing other elements. When all the elements
are placed in their proper positions, continue with suiting the values of their
properties. This can be done if pressing button ‘q’ from he keyboard. The same
result comes from Edit  Object Properties. The source vsin and the ground
(gnd) can be found in library analogLib.
Library
PRIMLIB
PRIMLIB
analogLib
PRIMLIB
PRIMLIB
analogLib
Element
rpoly2
rpoly2
res
cpoly
nmos4
vdc
Parameters’ values
R7=1000
R2=700
R8=100
C2 = 34,9998pF
DC voltage=2.8V
7. Adding wires
After all the elements are placed they should be connected with wires. Go to
Add  Wire (narrow) – 11th button from the left side in the schematic tool,
or press ‘w’ from the keyboard.
Once you have several wires drawn, you may wish to label some of them.
This might be done to affect a label to label connection, or to supersede the
name which the wire has inherited from the pin which it is connected to. To
do this, go to Add  Wire Name or the 13th button from the left side of the
schematic tool.
It is good in time to time to check your work for errors and to save it. This
can be done in Design  Check and Save.
II. Analog Simulation using Simulation Tool SPECTRE
To choose and start the simulation, go to menu Tools in schematic editor and
choose Analog Environment. The next you will see is a dialog window for
analog simulation Affirma Design Environment (ADE), shown in the
figure below:
Frame Design - information about the project that will be simulated (library,
project name and kind)
Frame Analyses – shows a list with chosen analyses
Frame Design Variables – shows a list with all variables which are used in
the circuit and will be simulated.
Frame Output – shows list of voltage/electricity which should be simulated,
visualized, or kept.
The buttons which are placed on the right side in ADE are subsidiary and
represent shortcuts to few of the main command in the menu:
1st button – Choose design;
2nd button – Choose Analyses;
3rd button – Edit variables;
4th button – Setup Outputs;
5th button – Delete;
6th button – Netlist and Run
7th button – Run Simulation
8th button – Plot Outputs
1. Choosing Simulator
The default simulator for ADE is SPECTRE. Anyway the simulator
can be changed from menu Setup - Simulator/Directory/Host
In the drop-down list you can choose the wished simulator. On other
hand from that form you can set the directory path where to save the
results.
2. Choosing analyses
In order to choose analyses in ADE go to Analyses  Choose. You
will see a form with all available analyses. To start the simulation,
press the button with green traffic light or choose Simulation  Run.
After the simulation is completed, there are few ways to visualize the
results. If few of the outputs were previously chosen for visualization,
they will be automatically shown in the Output frame. Otherwise go to
Results  Direct Plot, or choose Calculator from menu Tools.
3. Direct-current analysis (dc)
DC analysis is used to determine the operating point, to set the dc rate
per temperature, or to change some element’s parameter.
In order to make dc analysis, follow the steps:
1) Choose Analyses  Choose  dc;
2) Mark Save DC Operating Point;
3) Select Component Parameter and choose the element R8
which parameter r varies in range 50 to 500 with step
50
4) Press OK in order to start the simulation
5) To visualize the results go to Results  Direct Plot  dc.
Choose pins Vout, Vgate and Vin and press Esc.
6) To visualize the results for R8 per parameter, go to Results
 Direct Plot  dc, choose the pin Vout and press Esc.
In DC analysis it is possible to visualize the parameters’ values for an
element for given operating point. To do this, go to Results  Print 
Operating Point, and choose the desired element from the schema. On
the figure below you can see the parameters’ values for NMOS transistor
(nmos4)
4. Frequency Analysis (ac)
In order to run frequency analysis, go to Analyses  Choose  ac
from ADE window and follow the steps described below:
1) Choose ac;
2) Set the frequency as Sweep Variable and Sweep Range
from 1Hz до 100GHz. Set Sweep Type to Automatic;
3) Press OK to start the simulation;
4) In order to visualize the results :
 Results  Direct Plot  AC Phase, choose pins Vin
and Vout and press Esc.
 Results  Direct Plot  AC db20, choose pins Vin
and Vout and press Esc.
Фиг. 17. Фаза на напреженията във възли
“Vin” и “Vout”
5. Transient Analysis (tran)
In order to run transient analysis, go to Analyses  Choose  tran.
Set Stop Time box to some value in order to determine the time range for
simulation. Set the tran analysis accuracy and check Enable box.
To do the tran analysis follow the steps below:
1)
2)
3)
4)
Choose tran;
Set Stop Time to 10s;
Press OK to start the simulation
In order to visualize the results, go to Results  Direct
Plot  Transient Signal, check pins Vin, Vgate and
Vout and press Esc.