Integrated Circuit Engineering 2

Lab 1   L-Edit


Introduction

This lab is provided to help you to remember what you knew of L-Edit and the Scalable CMOS technology. The lab will cover in particular the use of good hierarchy to create design modules and the use of T-Spice simulation to characterize your designs. It is hoped that by giving examples which use good design practice it will encourage you to use similar practices within your own designs.

Changes in Tools for This Year

Example Library File

The library file, W:\TannerLibs\intro_lab\INTRO_LAB.tdb, contains two leaf cells, EX_INV and EX_NAND2.

Four representations of the inverter, EX_INV, are shown below:

The first two are the symbol and the transistor level circuit schematic of the inverter. The third is the stick diagram for the inverter using the standard colour coding:

Red Polysilicon
Green N diffusion
Yellow / Brown P diffusion
Blue M1
Purple (Magenta) M2
L.Blue (Cyan) M3
Black Contacts & Taps

The stick diagram represents the layout in a shorthand form, allowing us to identify the arrangement of transistors, conductors and contacts. Note that an N transistor exists where Polysilicon (red) crosses N diffusion (green) while a P transistor exists where Polysilicon (red) crosses P diffusion (yellow/brown).

The last of the representations is known as a layout abstract or simply a black box representation. When we draw gate level circuit schematics we use the symbol for the inverter since we are not concerned with the implementation of the inverter only its function. Similarly when we draw a module layout including inverters and other leaf cells, we prefer to use the abstract representation of the inverter since it tells us exactly what we need to know in terms of the location, name and conductor type of each input and output together with an outline which tells us the extent of the cell (without the clutter created by including internal detail).

The corresponding representations for the two input NAND gate, EX_NAND2, are:

The third cell is a ring oscillator module, EX_RING, constructed from 9 leaf cells (8×EX_INV, 1×EX_NAND2) plus interconnect.

The stick diagram for the ring oscillator uses the abstract representations of the leaf cells:

Note that the wiring of VDD and GND is implicit where two leaf cells are butted within a row since the VDD and GND ports of one abstract butt against those of the adjacent abstract. Note also that this module uses a strict two conductor routing strategy with metal 1 horizontally and polysilicon vertically (the exception being the vertical power rails to the left and right which must always be in metal).

Procedure

Copy and Examine Example Library

Take a copy of file W:\TannerLibs\intro_lab\INTRO_LAB.tdb and save it in your own user space. Open the new file using L-Edit.

Simulate Ring Oscillator Cell

Design and Simulate Loaded NAND Module

Create NOR2 Cell


Iain McNally

25-2-2003