Tutorial

Description

ELE 704 Analog CMOS Integrated CircuitsLaboratory One - Cadence TutorialProfessor Fei YuanSeptember 20111 Pre-LaboratoryPre-Laboratory must be completed and handed in prior to thecommence of the corresponding Laboratory Work1. Derive the voltage transfer function H(s) of the circuit in Fig.1.2. Obtain the zeros and poles of H(s).3. Determine the transfer characteristics of the circuit (low-pass, high-pass, or band-pass). Find the bandwidth of the passband.4. Sketch the Bode plot of |H(jω)| and its phase plot.5. Obtaintheresonantfrequencyω andthequalityfactorQofthecircuit.0VoVinR1=22kR2=75C=47nL=500mFigure 1: Schematic of RLC circuit12 Laboratory Work2.1 Cadence EnvironmentA. Start UpCadence is a set of computer-aided design tools for design, analysis, andverification of integrated circuits. To run Cadence, you need• Unix commands• Cadencetools: VirtuosoComposer,AnalogDesignenvironment(ADE)and Virtuoso XL• CMC’s cmosp18 design kitYour system has been pre-configured for that. To start Cadence fromyour home directory, type• cmosp18FirstRun (folder name)• cd cadence18• startCds -t cmosp18where folder name is the name of your lab folder under your home directory.Before create the folder, make sure your have enough space to finish all thelabs, e.g. 100MB.comsp18FirstRun (folder name): Newuserfirsttimemustrunthiscom-mand to build-up cadence environment automatically.startCds -t cmosp18: starts your Cadence software and launches the Ca-dence ...

Informations

• Publié par: Zoev
• Nombre de lectures: 32
• Langue: English

Extrait

ELE

704

Analog

CMOS

Integrated

Laboratory One - Cadence

Professor Fei Yuan

September 2011

Circuits

Tutorial

1 Pre-Laboratory

Pre-Laboratory must be completed and handed in prior to the commence of the corresponding Laboratory Work

1. Derive the voltage transfer function H ( s ) of the circuit in Fig.1. 2. Obtain the zeros and poles of H ( s ). 3. Determine the transfer characteristics of the circuit (low-pass, high- pass, or band-pass). Find the bandwidth of the passband. 4. Sketch the Bode plot of | H ( jω ) | and its phase plot. 5. Obtain the resonant frequency ω 0 and the quality factor Q of the circuit.

Vin R1=22k

C=47n

Vo R2=75

L=500m

Figure 1: Schematic of RLC circuit

1

2 Laboratory Work 2.1 Cadence Environment A. Start Up Cadence is a set of computer-aided design tools for design, analysis, and verification of integrated circuits. To run Cadence, you need • Unix commands • Cadence tools: Virtuoso Composer , Analog Design environment(ADE) and Virtuoso XL • CMC’s cmosp18 design kit Your system has been pre-configured for that. To start Cadence from your home directory, type • cmosp18FirstRun (folder name) • cd cadence18 • startCds -t cmosp18 where folder name is the name of your lab folder under your home directory. Before create the folder, make sure your have enough space to finish all the labs, e.g. 100MB. comsp18FirstRun (folder name): New user first time must run this com- mand to build-up cadence environment automatically. startCds -t cmosp18: starts your Cadence software and launches the Ca- dence Command Interpreter Window (icfb) where you can check your current version of Cadence tools and the version of the design kit being used.

2

B. Initialization Files The Cadence environment uses three major initialization files and one model file of cmosp18. cds.lib: sets the path to the libraries used in your design. This file is cre- ated in your current folder when you start Cadence. When you start Cadence for the first time, cds.lib will be automatically copied to the current directory. .cdsinit: Customizes specific simulation environmen .cdsenv: sets global Cadence environment.

C. Where to Find Help ‘open book’ : Online documentation for most Cadence tools. Access through: icfb | CMC Gateway | Start Cadence Documentation . CMOS18 technology information: design rules and model parameters. Access through: icfb | CMOSP18 | CMOSP18 documentation | launch Netscape for CMOS Docs or f ile : CM C tools cadence 2008 a I C 61 toolssun 4 vdf I I  locallibcmosp 18 cmosp 18 − docshtml Up to this point, you have learned how to start Cadence software and where to find on-line help. Before jumping to Cadence tools to start your circuit design project, it is beneficial to have a look at Cadence facilities that support the basic operation.

2.2 Cadence Facilities A. The icfb Window When Cadence starts, it brings up the icfb (Integrated Circuit front-to-back) window, as shown in Fig.2. It is Cadence’s Command Interpreter Win- dow that can be thought of ‘Cadence Shell’. It is through icfb window that 3

Figure 2: icfb window

you can do all of your Cadence tasks, including file management and program execution.

B. Libraries, Cells and Views Cadence uses the hierarchy of Library | Cell | View to manage design data. Cadence stores design data into libraries that are not transparent to external file systems. How each library corresponds to a physical path in the file system is registered in the file named ‘cds.lib’, which is one of the three major initialization files mentioned earlier. This file can be modified using icfb | Tools | Library Path Manager . The first thing you should do in Cadence is to create your own library, we will come back to this point in ‘Cadence Walk Though’ shortly. A cell contains Cadence’s design data, or more specifically, the data of the designed circuit. Each cell has at least one view that is the representation of the cell. Fig.3 shows the Library Manager window. Each time when a new library or a new cell is created, a new item will appear in the corresponding column of the library manager. Three libraries that will be most frequently used in the laboratories are

• cmosp18 - this library contains the cells of 0.18 µ devices, such as tran- sistors, capacitors, and resistors.

• basic - this library contains ideal components of circuits.

4

Figure 3: Library Manager window

• analogLib library contains basic components for analog circuits. It also contains various types of independent and dependent sources.

2.3 Design Flow In this section, we will go through the basic design steps of Cadence CAD tools.

• Step 1 - Create Schematic

– Instance transistors and other elements from libraries – Create the schematic of the circuit by connecting elements to- gether and modify their properties. – Create the ’Symbol’ view of the schematic view.

• Step 2 - Simulation

5

– Use simulation and waveform viewers to modify circuit parameters until design specifications are met.

• Step 3 - Layout and DRC

– Map the schematic onto silicon – Layout must must follow the design rules of chosen technology and pass design rule check (DRC).

• Step 4 - Extraction and LVS

– Create post-layout schematic from layout. Both the parasitic ca- pacitances and resistances can be extracted from the layout in this step. – Perform LVS (Layout versus schematic) to verify whether the post-layout schematic matches the original schematic.

• Step 5 - Post-Layout Simulation

– Simulate extracted view (post-layout schematic) by taking into account the effect of parasitic capacitances and resistances. – Using simulation results to modify the layout until design specifi- cations are met.

Up to this point, you have known the overall picture of the design flow. In sections that follow, we will use a simple RLC circuit as an example to walk you through these basic steps.

2.4 Create Schematic In this laboratory work, You are required to do the followings

• Create the schematic of the RLC circuit.

6

• Create the symbol view of the circuit. • Create a test fixture circuit for testing the RLC circuit. • Perform transient analysis, AC analysis, and DC analysis on the circuit using Cadence’s Spectre analog simulator. • Provide a detailed comparison between the analytical results from your Pre-Laboratory Report and those obtained from the Laboratory Work.

A. Create New Libraries and Schematic Views 1. Create New Libraries

Figure 4: Create library window

It is necessary to have a separate library to store your design cells and their views. To do that

• From the icfb menu, select File | New | Library • Navigate to the cadence18 directory (if not already there) • Type in ‘mylibs’ as the name of your new library

7

• Select to attach to an existing techfile , click OK , then select the cmosp18 library when prompted. By selecting the techfile, you will be able to use the cells from cmosp18 library for your design.

2. Create new design cells

Figure 5: Create schematic view window

• From the icfb menu, select File | New | Cellview . You are prompted for the library to place the new cell in and what type of view you are creating. • Select ‘mylibs’ that was created in the previous step and ensure Composer-Schematic is selected as the tool for your new cell. Note that ‘schematic’ is the default name of the view. • Enter ‘rlc’ as the cellname and select OK to open the new cell in composer.

The rest of this section describes the steps to create the rlc circuit shown at Fig. 1 in schematic view.

8

B. Add Components and Wires When creating a schematic, you place instances that were created previously, edit their properties e.g. resistance, capacitance, width, etc, and wire them together. In the case of the RLC circuit, you will place two resistors, one capacitor, one inductor and ground. You wire the devices together using the wire tool, and wire snapping, and then edit the property of the devices to set R 1 =75kΩ, R 2 = 75Ω, C=47nF, and L=500mH. 1. Instantiate Components

Figure 6: Add instance window

To place a resistor, follow these steps from the main composer window

• Click on the Instance Icon. The Add Instance window will appear as shown in Fig. 6. Click on the Browse button.

9

Table 1: Component value of RLC circuit Component Library Cell View Value R1 analogLib res Spectre 75 kΩ R2 analogLib res Spectre 75 Ω C analogLib Cap Spectre 47 nF L analogLib Ind Spectre 500 mH Ground basic gnd symbol N/A

• In the browse library window, select cmosp18 library, resistor cell, and symbol view. • Move the cursor to the Composer Schematic window, the re- sistor symbol follows. Also, note that the Add Instance window has expanded to display other parameters. Before you click on the schematic window to place the resistor symbol, edit the form, modifying the resistance value to 75kΩ. IMPORTANT: Do not get concerned with all of the seemingly irrelevant parameters. They are used for more detailed simulations and other applications. • Click in the composer window to place the resistor. • Another resistor symbol follows the cursor. Place it in the window then click on Cancel on the Add Instance window. The form disappears. • In the same way in which you added the resistor, add the other instances from the library, cell, and view as indicated below. • To rotate an instance in Schematic Composer window, click once on it to select (left-click with the mouse), then middle-click to open the auxiliary menu. Select Rotate .

2. Add I/O pins

10