ECE122 – Digital Electronics & Design

Tanner Tools Tutorial

Ritu Bajpai

Objective of the lab

● To develop an understanding of design and simulation of digital logic circuits.

● To get a basic understanding of layout of electronic circuits.

● We will use Tanner tools for design and simulation.

● This lab introduces us to Tanner tools.

Introduction to Tanner tools

● Tanner tool- simulation tool for the class

● Upgraded from last year● Some slides may look different as you

will see on your computer● Slides will be updated to correspond

with the new version of Tanner as we advance into the semester

Tanner tools consists of the followingL-Edit: Layout editing

LVS: Layout vs. Schematic

S-Edit: Schematic Entry

T-Spice: Simulation

W-Edit: Waveform formatting

This is S-Edit

For creating new design go

File->New->New design

Enter design name and the folder name where you want to save your work.

Recommendations

● Make a new folder in your name and always save all your work there.

● Use same system each time so that you don’t have to transfer your old files to another system if needed.

● Create a backup of your work if needed as the lab computers are formatted from time to time.

Now go to Cell->New View

Hit OK to start with new cell schematic design

Levels of design in S-Edit● The highest level in the S-Edit design

hierarchy is the design file. Files contain modules, which can contain primitive objects or reference to other modules.

● A module can further have pages.● S-Edit has 2 viewing modes, Schematic

mode and Symbol mode. We can switch between 2 modes using the tabs in the tool bar or using a question mark (?).

Select tool Draw wire

Cap Node

Label Node

For more help with S-Edit go to

Help->Tutorial

Library file path

C:\Desktop\Student\My Documents\Tanner EDA\Tanner Tools v15.0\Process\Generic_250nm\Generic_250nm.tanner

Click here to add libraries

Browse the library file from the path above and hit OK.

There are other libraries in the process folder. Feel free to add them and see what components they have. For example we will add spice_components and spice_commands from the library “standard_library”.

Now we will instance first element NMOS from the library Devices and hit done.

Some useful tips● To move an object: Use center wheel of

the mouse.● For zoom in and zoom out use + and –

respectively from the key board.● To view/edit object properties, select

object and use CTRL+E.● Do not use space in your design names. ● Do not use special characters in port

names.

Introduction to MOSFET● A MOSFET can be

• PMOS

• NMOS● A MOSFET is a four terminal device.

Four terminals are:• Gate

• Drain

• Source

• Bulk● A MOSFET is symmetrical device unlike

a BJT which means either terminal can be drain or source unless connected in a circuit.

Introduction to MOSFET

● For a PMOS source is always connected to highest voltage in the circuit.

● For an NMOS source is always connected to lowest voltage in a circuit.

● The bulk is always shorted to the source for both devices.

Introduction to MOSFET● The bulk terminal is identified by an

arrow.● We can distinguish PMOS symbol from

NMOS symbol as follows:• PMOS bulk has arrow coming out .

• NMOS bulk has arrow going in. (Tip: remember ‘in’ sounds like N.)

• PMOS gate has a bubble attached to it.● There can be different symbols for

PMOS and NMOS for example the bulk may not be shown but the above points hold good for the MOSFETS we will be using from SCMOS library in S-Edit.

Schematic design of an inverter

● Today we will design an inverter schematic in S-Edit.

● In this class we will design CMOS based logic circuits.

● Thus an inverter consists of a PMOS and an NMOS connected in series with PMOS source connected to Vdd and NMOS source connected to Gnd.

● Input is applied at the gates.● Output is collected from the drains

which are connected together.

Vdd from library Misc

Gnd from library Misc

PMOS from library Devices

Input portOutput port

Now we are ready to create a symbol for the schematic design

Draw the symbol of the module which clearly represents the function if possible.

Create a new design file just as you did for inverter now to make the schematic for the inverter test bench.

Add libraries and make sure you also add inverter as a library so that you can instance it.

Voltage sources from spice elements

library

Print voltage probe from spice commands

Voltage source properties can be modifies from here

Now we will set up the simulation settingsClick to pop up the set up window

Browse the library file

My Documents\Tanner EDA\Tanner Tools v15.0\Process\Generic_250nm_Tech\Generic_250nm.lib. Add a space followed by letters TT at the end of the path. This is must for spice to recognize this path.

Select Transient/Fourier analysis

Hit OK and click the green play button on the top left

Types of analysis

● DC Operating Point Analysis.● DC Transfer Analysis.● Transient Analysis.● AC Analysis.● Transient Analysis, Powerup Mode.● Noise Analysis.

Types of analysis● DC operating point analysis: It finds the

circuit’s steady-state condition, obtained (in principle) after the input voltages have been applied for an infinite amount of time.

● DC Transfer Analysis: It is used to study the voltage or current at one set of points in a circuit as a function of the voltage or current at another set of points. This is done by sweeping the source variables over specified ranges, and recording the output.

Types of Analysis● Transient Analysis: It provides

information on how circuit elements vary with time.

● AC Analysis: It characterizes the circuit’s behavior dependence on small signal input frequency.

● Transient Analysis power up mode: Some circuits do not have a DC steady state so it is difficult to specify there initial state. This is done using power up option of the .tran command. It sets entire circuit to zero for time equal to 0.

Propagation Delay● Propagation Delay is the amount of time

it takes a change of input to appear as a change on the output.

● Propagation Delay is measured from the 50% point on the input signal to the 50% point on the output.

Input

Output

tpHL

Transition time

● High-low and low high transition times at the output of a gate are defined as tHL and tLH between the 10% and 90% points.

tLH

10%90%

tHL

10%90%

Gate Delay

● The load capacitance severely affects the gate delay.

Inv1

Inv2

Simulating NAND gate

● Next we will make a NAND gate using p and n MOSFET and test its performance.

Note parameters W=2.50u and L=0.25u

NAND GATE

TEST BENCH FOR THE NAND GATE

NAND GATE

TEST BENCH FOR NAND GATE

NAND GATE

TEST BENCH FOR NAND GATE

tpHL

Record the propagation delay

● Record tpHL and tpLH for the NAND gate.

● Record the waveform for the same.

Lab Reports

● Strictly adhere to the lab report format and other instructions on the website

● No late submissions without prior permission