IN3170/4170, spring 2020, mandatory labratory exercise 2: Gate delay - - PDF document

IN3170/4170, spring 2020, mandatory labratory exercise 2: Gate delay and nFET intrinsic gain (deadline 16-Mar-2020, 10:00!)

• P. H¨

afliger & Sebastian Wood Institute of Informatics University of Oslo e-mail: hafliger@ifi.uio.no February 17, 2020

Abstract This second lab is ment to show some analog limitations of digital circuits and a first glimpse of how to implement electronic amplifiers as well. It is the second in a series of three labs that will be graded and will count 40% towards the final grade. The first lab has been ’pass’ or ’fail’ with a requirement to pass. This second lab and the third lab will give you points that will weigh 20% towards your final course score. The deadline is March 16th, 10:00! It is a hard deadline! Do not miss it! Plan to submit well ahead of the deadline! We will use devilry.ifi.uio.no for submission of you lab report.

1 Lab Rules

1.1 Safety

Voltages over 40 Volt can in some cases be harmful, even though it usualy requires more than that. The lab equipment is thus not able to provide voltages higher than 36V. Do not use equipment other than that provided in the lab! If a part of the skin is covered with a conductive fluid or is pierced and exposed to such voltages, a current could bypass the “insolator” of the skin and run through the body. If this current passes through the heart it can cause fibrillations or even cardiac arrest. Even higher more extreme currents could also give rise to internal burns. If this happens to anybody or something else happens in the lab, seek medical help immediately: heart fibrillations can last and cause trouble long after the incident. Also notify the person in charge of the lab. 1

Some electronic components can explode if they are exposed to high currents. This is important to remember when working with electrolytic capacitors. How- ever, none of the capacitors provided in the lab are electrolytic capacitors. Never bring your own electronic components into the lab!

1.2 Conduct

Good routines are necessary to make the work in the lab effective and safe:

• Food and drinks are prohibited from every lab.
• In general everybody is responsible for keeping the lab tidy.
• Always turn off the power supply before you start adding and/or removing

components.

• Use an ESD protection wrist strap when handling ICs and other sensitive

components.(ESD: electrostatic discharge)

• Always clean up after using equipment and tools:

– Turn off all equipment, except for lab computer. – Throw away cutoffs and vacuum clean the desk, chair, and floor if nessesary. – Place all components you have used back to their respective places. (Do this while you work, if you have a component you don’t use anymore, put it back.)

• When you leave; the desk should be clean and ready for the next group.
• Read the information posters in the lab describing what to do in case of

fire or medical emergency.

2 Report and Group Assignments

2.1 Requirements for the Lab Report (read carefully!)

You are required to execute the tasks and answer all the questions posed below and to submit a report on your work. The report needs to be explaining clearly what you have done, how you have done it, what the results were and what you conclude from them. Make sure to answer all questions! Supply the report with drawings of the circuits (including the values of the components and parameters you used where appropriate, e.g. bias voltages/currents, component sizes etc.) and measurement setups, and show your measurements in graphs! Use labels in the schematics that you draw, such as M1, M2 (M is often used fro labelling CMOS transistors), opamp1, I1, V1 etc. You should then use those labels in your text, since it is much easier to write: ’transistor M1 in figure 1’ than ’the transistor third from the top and second from the left in the righthand side 2

circuit in figure 1’. MANDATORY: Include a photograph of your circuit into the report!

2.2 Graded Mandatory Group Assignments

Note that this is part of the courses exam and strict rules apply as described in the document http://www.mn.uio.no/ifi/english/studies/admin/mandatory-assignments/ index.html. The page explains the significance of mandatory assignments in a course and in particular group assignments. It also specifies your responsibility to not plagiarize anybody else’s work and that you are required to conduct and understand your own experiments and obtain your own results, while you are still allowed and encouraged to exchange advice and experiences also between groups. Each group must deliver a written lab report using the Devilry online sub- mission system before the hard deadline indicated in the title. Note that you can submitt multiple times and the last submission before the deadline will be graded, so it might be a good idea to plan to submit preliminary versions well before the deadline. The points given for this lab assignment will determine if the lab assignment is accepted or rejected. You will need to pass this lab assigment in order to be admitted to the exam. The next two lab assignments will be weighted as 20% of the total score of the course, i.e. your final grade. Each task is labelled with how many points it will contribute towards the score.

3 Lab Task

3.1 Introduction

Transistors are intrinsically well suited to implementing abstract logic functions. As long as one operates them far from their top speeds and at their nominal supply voltages this is quite straight forward and unproblematic. However, aiming for top performance, the differences between the logic/binary abstraction and real world circuit behaviour become apparent and extra caution and deeper knowledge is required. Task 1 illustrates some effects of the speed limitation of real world digital circuits. In task 2 we get a first glimps of the analog use of transistors, i.e. their use in amplifying circuits. Amplification is a very fundamental requirement in signal processing, be it in artificial machines or living organisms: whenever signals are combined, analysed, and finally result in a reaction of a system, amplification is important to maintain signal quality along the processing chain. Task 2 explores the ’intrinsic gain’ of a transistor, i.e. its upper limit for voltage gain if it is used as a simple amplifier. 3

3.2 Tools

• The NI-ELVIS bord and plug-in bread bord

You shall use a bread board to plug in cables and discrete components to compose your test circuits. The bread bord can be removed from the socket in the ELVIS bord and each group can keep one for the duration

• f the course. Thus, once you are done for the day you can leave your

components in place and lock your bord away or take it home with you until your next lab session. The ELVIS bord has some built in instruments that are displayed on the computer at each work place. You shall use those instruments to characterize your circuit. Some general advice: plan your layout of components and cables on the bread bord before you start plugging them in and try to make things compact and organized.

• The NI ELVISmx Instrument Launcher

BEFORE you launch the NI ELVISmx Instrument Launcher you should switch on the ELVIS board, such that the software (SW) recognizes the hardware (HW) correctly. Note that there are two power switches, one

• n the right hand side on the back of the board and one on top of th

board also on the right near the back. You may launch the NI ELVISmx Instrument Launcher from the icon on your Windows desktop in the lab and you will get a list of icons representing the various instruments that are built in into the ELVIS board. See figure 1. Note that the interface looks now a bit more modern than in the description of IN1080.

• The NI ELVISmx 2-wire VI Analyzer

Another NI ELVISmx instrument i the 2-wire VI analyzer and when you click it its front panel pops up and looks as depicted in figure 2. It let’s you sweep a voltage and measure a current accross a device/circuit. The connections on the bread board left hand side between which you need to place your circuit under analysis are DUT+ and DUT- . For more help, press the ’help’ button. Note that this instrument will execute a series of measurements that you could have performed by hand. This is

• ften a good thing, but has some pitfalls: you should know in some detail

how the results are obtained, because sometimes results of automated measurements can be something else than what you think they should be, because they are not exactly obtained as you think they are ...

• NI ELVISmx Variable Power Supply

Start it from the Instrument Launcher and consult the help pages or ask your lab assistant if something is unclear.

• The NI ELVISmx Oscilloscope

4

Figure 1: The NI ELVISmx Instrument Launcher 5

Figure 2: The NI ELVISmx 2-wire VI Analyzer Virtual Instrument 6

Figure 3: The NI ELVISmx Oscilloscope Virtual Instrument 7

Figure 4: Connections on the ELVIS II bread board, with the oscilloscope con- nections highlighted. 8

When you open the Oscilloscope in the instrument launcher the virtual instrument pops up like in figure 3. You’ll have two channels to observe waveforms on the oscilloscope that are conected to BNC ports labelled CH0 and CH1 on the ELVIS board, the upper left red circle in figure 4. Per default they should be connected with BNC cables to ports BNC1 and BNC2 such that you can connect them by plugging in wires into the bread board to the right of the labels BNC 1 ± and BNC 2 ± (the lower red circle). Note that you should connect the minus terminal to a GROUND. You can briefly check out its function by connecting the output of the function generator (output labelled FGEN on the breadboard and you need to launch its VI) to one of the channels and play around with the various knobs. More help for the instrument is available if you press on the help button in the VI front panel. That’s true for all instruments! An important function/button is the ’write to log’ which will export the graph in a text file that you can make readable by MATLAB with a few simple edits. Then you can create nice graphs for your report or do some more adavanced analysis of the data in MATLAB.

• NI ELVISmx Function Generator

Start it from the Instrument Launcher and consult the help pages or ask your lab assistant if something is unclear.

• CMOS transistors

The IC that contains a set of individual transistors is labeled ’MC14007UBCP’. There may be other IC’s containing the number 4007 in their name and those contain the same arrangement of transistors with the same pin- assignment and can also be used. The difference is that they are in a different CMOS process technology, so the transistor properties will be

• different. A data sheet will be available in the lab or through the course

pages that shows which pins are to be used as bulk, source, drain, and

• gate. Do not forget to connect the power pins (14 and 7)!
• MATLAB

We will be using MATLAB for some excersises and it’s the best tool for plotting all of your results as nice graphs. An important function/button on all ELVIS VIs is the ’write to log’ which will export the graph in a text file that you can make readable by MAT- LAB with a few simple edits. Then you can create nice graphs for your report or do some more adavanced analysis of the data in MATLAB. Thus, you should bring a working knowledge of MATLAB to this course. If you have none, get a crash course from a fellow student who has used it! It is a powerful mathematics tool with a command line interface. One useful function is ‘help’. ‘help <command name>’ will display an explanation

• n how to use ‘<command name>’. Another help function that helps you

find functions that you do not know the exact name of is ‘lookfor’. Type ‘help lookfor’ to learn more. 9

3.3 General Advice

• Draw a schematic before you start assembling components on the PCB!

Label pins on the PCB and in the schematics (!) clearly in order to keep your overview. Debuging will be much, much easier that way!

• Come to the lab with a work plan: Read the entire lab task beforehand

and make a plan how to proceed. Put yourself a goal for a lab session. Read the relevant book chapters in order to understand the entire lab. Be ready with questions already before the lab if there are still things unclear.

3.4 Lab Tasks

Task 1 (8p): Use the transistors on the MC14007UBCP IC to build a cascade

• f inverters with 10V supply. Connect a 1uF capacitor as a load on the

inverter output of the last inverter in the chain. This capacitor should be big enough to see a significant (in the order of 1ms) propagation delay if you use only one inverter. If that is not the case, increase the capacitor size until you get an obvious propagation delay. Document that delay as your ’starting point’. Use an arbitrary number of inverters (more than zero!) and use an arbitrary number of transistors in parallel for each inverter, except for the first one which needs to be composed as a ’normal’ small inverter with two transistors only. Try to make it so that the propagation delay of the input signal (a sharp step from the signal generator) is as short as possible. Use the oscilloscope to record both the input step and final output. Document your experiments along the way and show a good measurement of the propagation delay in each case! (Note: it is sufficient for a maximum score to show one variant with improved propagation delay.) Task 2 (4p): Use an nFET from the MC14007UBCP and determine it’s in- trinsic gain for with 10V supply and a selection of at least 8 different points of operation for vGS. How do you do that? Document thoroughly! (Hint: maybe you can use results from lab1?) 10