Cells Manipulation in L-Edit

Digital System Layout options:1. Full Custom. Every detail of the integrated circuit layout needs to be completed. All gates

Digital System Layout options:y g y p g

must be designed, drawn, and simulated.

Advantages: reduced area and performance improvements.Disad antages: increased man fact ring and design time more comple it in theDisadvantages: increased manufacturing and design time, more complexity in the computer-aided design (CAD) system, and a much higher skill requirement on the part of the design team. It is appropriate for chips having large production runs.

2. Cell Based. Layout designs are based on exiting layout cells stored in a libraries. These libraries are provided by the device manufacturer. Using the software, the interconnections can be done manually or automatically by what is called Place and Routing..

Advantages: Fast, design can be changed easily and not need much higher skills in layout.Disadvantages: increased area, less performance.

• In this session you start layout a digital system according to cell based.

Cells Maniulation in L EditCells Manipulation in L-EditCells Maniulation in L-Edit• L-Edit provides very powerful commands for creating, editing, and

Cells Manipulation in L Editp y p g g

applying cells in layout drawings. These are accessed from the Cell Window of the Menu Bar. cell libraries will be available when the file is opened.opened.

Cells Manipulation in L-Edit• Every drawing in L-Edit is labeled with a file name,

Cells Manipulation in L Edity g ,

with the default name being Layout1. The cell name is assigned to the drawing on the screen; the default g g ;name is cell0.

Cells Manipulation in L-EditCells Manipulation in L Edit

• It is possible to create cells and store them in the memory. Stored cells can be accessed using the Instance Command. When this command is executed, a list of currently available cells is displayed. The

Cells Manipulation in L-Edit• All integrated circuits require power distribution bus lines to

Cells Manipulation in L Edit• All integrated circuits require power distribution bus lines to

supply current to the gates. In CMOS, usually a positive VDD and a ground or VSS must be routed across the die. It is gimportant to use geometrical structure that accommodates the shape of the logic cell as shown in the figure below.

Cells Manipulation in L-Editp

di t ib tipower distribution bus linesbus lines

Cells Manipulation Example• Suppose you want to draw the layout of the following D-Flip

p p

Flop.

• If you have the layout of 3-inputs Nandas a standard cell in your Library then it will be easier to draw the layout.

• But if you don’t have that Library, create a cell for the 3-inputs Nand and use it to create the D-Flip Flop. That’s will be done in this session.

DFF Cells Manipulation Example• Run L‐Edit and Save the file as progect.tdb

DFF Cells Manipulation Examplep g

DFF Cells Manipulation Example• From main menu, select Cell>> Rename and change

p p

cell name from Cell0 to nand3

DFF Cells Manipulation Examplep p• Draw the layout of the 3-input nands as below, check the design

rules extract to spice and simulate to be sure the layout is correctrules, extract to spice and simulate to be sure the layout is correct.

DFF Cells Manipulation Examplep p• From main menu, select Cell>> New ,put the new cell name as

dfilipflop as belowdfilipflop as below

DFF Cells Manipulation Examplep p• New empty cell will be opened, with dflipflop as a name in the

project tdb fileproject.tdb file.

DFF Cells Manipulation Examplep p•From main menu, select Cell>> Instance ,and select nand3 cell.

DFF Cells Manipulation Examplep p•The nand3 cell will be inserted in the dflipflop cell.

DFF Cells Manipulation Examplep p•You needs six nand3 cells, select Cell>> Instance ,and choose

d ll i b d fi llnand3 cell again because you need extra five cells.

DFF Cells Manipulation Examplep p

DFF Cells Manipulation Examplep p•The six nand3 cells are shown but without connections between themthem.

DFF Cells Manipulation Examplep p•Do the extra connection to have D Flip Flop. Check design rules, extract to spice and make sure that the layout work correctly as DFFextract to spice and make sure that the layout work correctly as DFF.

Cells Manipulation Assignment• Before you have created a file that contains two cells the

Cells Manipulation Assignment• Before you have created a file that contains two cells, the

inverter cell and the 2-inputs Nand cell.

• Modify the layout of the Nand gate such that it has the same speed of the inverter.p

• In the same file create a new cell for 2-input Nor also has the psame speed of the inverter.

• Use the three previous cells, to draw a 3-inputs And gate. Verify the layout with SPICE.