Unix For VLSI Industry - Part 1

Unix is universal and lot of Industry is using this. But still in our education system, it's not part of curriculum. And that's the reason lot of Students faces issues during Interview or after joining companies. Today, I am going to capture few of the commands, I have used in my career and I wish it will help everyone. From Interview point of view, if you will practice to all these - I am sure you will be at good position.

UNIX Commands

• Few commands- which are not that important but still good to know
• date
• whoami: Who Am I - Tells you your user information.
• clear
• ps
• kill
• basename / dirname : extract file / directory name from full path
• touch: change file timestamp
• Commonly used commands
• echo : print command
• env:
• df
• head / tail : returns first / last lines of a file
• more
• wc : word count on files
• Must known command :)
• sort : used to sort files in lexicographic order
• cat: concatenate files and print
• ls (it's options)
• cd
• mkdir
• rm
• cp
• chmod
• mv
• pwd
• grep (it's options): find regular expressions in files
• vi
• awk
• xterm
• man
• find: find files by criteria
• diff: find differences between files
• tkdiff
• which

Redirection and pipes: Apart of this there are few processes which we uses very commonly to handle the output of a particular command.

• prog redirection file
• < : redirect stdin
• > : redirect stdout
• >> : append stdout
• >& : redirect stdout and stderr
• >>& : append stdout and stderr
• prog1 pipe prog2
• | : redirect stdout of prog1 to stdin of prog2
• |& : same, with stdout and stderr

Unix Concepts: Understanding of below concepts are necessary.

• Relative Path and Absolute Path
• Alias Concepts
• Tool Binary concepts : It's similar to exe in windows

VI Editor: Few things in the VI Editor (it's very powerful editor in Unix environment).

• How to Open a file
• How to Close a file
• How to Save file
• Write-append
• Set number
• Set nonumber
• Search – reverse and forward
• Search and replace – prefix, suffix
• Delete character
• Delete line
• Delete para
• Jump to any line number
• Jump to Last line
• Figure out total line and name of file

In next article, I will try to show you the use model of few of the important commands. Also, I will try to update this list - If, I can figure out any command I have missed here.

Transmission | Pass Gate - Assignment

Transmission gate or say Pass transistor (NMOS pass transistor and PMOS pass transistor) are one of the concept which is usually asked by Interviewer and most of the time candidates become confused. I will explain the concepts some other time but right now if you know then practice is very important or you should know what all they can ask and how they can twist the questions.

Please try to solve below questions. And prepare yourself for any interview.

Q.1) Implement a Logic Function Y=((A+B)CD)'. Size the NMOS and PMOS devices so that the output resistance is the same as that of an inverter with an NMOS W/L = 4 and PMOS W/L = 8.

Q.2) Implement a Logic Function Y=((A' + B'(C' + D' + E' )G' using complementary CMOS. Which input pattern(s) would give the worst and best equivalent pull-down resistance.

Q.3) There is one parameter of an n-channel transistor that is much “better” than the same parameter for the p-channel transistor. This parameter characterizes the major reason why the n-channel transistor offers better performance than the p-channel transistor in circuits using these devices. What is this parameter and how much better is it?

Q.4) Draw the Cross Sectional view of the below given Top View and also tell the device name.

Q.5) Draw the Top view for the given below Cross Sectional view. Define all the layers used in Top view

Q.6) Predict the Vout you can assume VTP as Threshold Voltage of PMOS.

Q.7) Draw an XOR gate using CMOS Structure and using Pass Transistor Logic. Explain the Difference between the two.

Q.8) An NMOS pass-transistor network is supposed to implement logic AND function Y = AB. Please add appropriate signals in the boxes, such that the circuit works properly.

Q.9) An NMOS pass-transistor network is supposed to implement logic OR function Y = A+B. Please add appropriate signals in the boxes (above fig), such that the circuit works properly.

Q.10) Add minimum number of PMOS transistors to the circuit shown below, such that it has a full swing at its output for any combination on its inputs.

Q.11)

1. For the circuits shown in Fig 1 and Fig 2 the function implemented is same. Is this statement True or False.
2. If input E arrives last amongst the signal which of the circuit Fig 1 or Fig 2 is more optimized in terms of speed and why?
3. Which of the circuit will be affected more by body bias Fig 1 or Fig 2 assuming all inputs are arriving at same time

Concepts around these questions and how you are going to analysis - I will discuss and let you know soon.

-Prepared By Niti Gupta
(Director of eLearning and university Program)
(VLSI Expert Private Limited)

-Supervised By Puneet Mittal
(Founder & Director)
(VLSI Expert Private Limited)