vlsi project report

A

PROJECT REPORT

ON

“4-BIT BARREL SHIFTER”

Ronak D. Thakare (Roll No:M-17)

Viraj S. Wagh (Roll No:M-27)

Kiran M. Malang (Roll No:M-28)

Pranil R. Waghale (Roll No:M-30)

Nikhil U. Dantkale (Roll No:N-23)

DEPARTMENT OF ELECTRONICS ENGINEERING

VISHWAKARMA INSTITUTE OF TECHNOLOGY

(An Autonomous Institute, Affiliated to Pune University)

Academic Year 2012-13

CERTIFICATE

VISHWAKARMA INSTITUTE OF TECHNOLOGY

Department of Electronics Engineering

This is to certify that

1. Ronak D. Thakare (Roll No:M-17)

2. Viraj S. Wagh (Roll No:M-27)

3. Kiran M. Malang (Roll No:M-28)

4. Pranil R. Waghale (Roll No:M-30)

5. Nikhil U. Dantkale (Roll No:N-23)

have submitted a project on the topic “ 4-BIT BARREL SHIFTER ”

in Mixed Signal VLSI Design LAB (VLSI Honor) for the academic year 2012-13.

Prof. A.V. Pedgaonkar A.M.Chopde

Assistant Professor Head of the Department

Electronics Engineering

ACKNOWLEDGEMENT

It is matter of great pleasure for us to submit this project report on

“4-BIT BARREL SHIFTER”, as a part of curriculum for award of

“Bachelor of Engineering in Electronics”.

We are thankful to our project guide Prof. A. V.

PEDGAONKAR Assistant Professor in Electronics Engineering

Department for her constant encouragement and able guidance.

We are also thankful to Prof. A. M. Chopde, Head of

Electronics Engineering Department for his valuable support. We take this

opportunity to express our deep sense of gratitude towards those, who have

helped us in various ways, for preparing our project. At the last but not least,

we are thankful to our parent, who had encouraged & inspired us with their

blessings.

Ronak D. Thakare (Roll No:M-17)

Viraj S. Wagh (Roll No:M-27)

Kiran M. Malang (Roll No:M-28)

Pranil R. Waghale (Roll No:M-30)

Nikhil U. Dantkale (Roll No:N-23)

TABLE OF CONTENT

Sr

No.

Content Page No

1. Introduction 6

2. Implementation of Barrel Shifter

using 2:1 Multiplexer

7

3. Transistor Level Diagram of 2:1

Multiplexer

8

4. Code For 4-Bit Barrel Shifter using

2:1 Multiplexer

9

5. Output waveforms of Barrel Shifter 11

6. Advantages of Barrel Shifter 12

7. Applications of Barrel Shifter 13

8. Conclusion 14

9. Bibliography 15

ABSTRACT

A barrel shifter is a combinational logic circuit with n data inputs, n data

outputs, and a set of control inputs that specify how to shift the data between

input and output.

In this project we have implemented 4-Bit Barrel Shifter which has 4 data

inputs D0,D1,D2,D3 and 4 data outputs Y0,Y1,Y2,Y3 using VLSI Technology. Three

modules have been designed which consist of four 2:1 Multiplexer in each module. Each

module has one select line. Select lines of first and third module determines how many

positions bits to shift. Select line of second module specifies shifting of data either to left

or right. Third module provides you your desired output.

We have implemented 2:1 mux using transmission gates which requires 6

transistors. Thus we have implemented 4-Bit Barrel Shifter using 72 transistors.

We designed a 4 bit Barrel Shifter that shifts data from an input to an output

depending on the combination of two select lines. Our design of the Barrel shifter allows

for an increase in the number of input bits without having to modify the existing design.

1. INTRODUCTION

A barrel shifter is a digital circuit that can shift a data word by a specified

number of bits. It can be implemented as a sequence of multiplexers (mux.), and in such

an implementation the output of one mux is connected to the input of the next mux in a

way that depends on the shift distance.

A barrel shifter that is part of a microprocessor CPU can typically specify the

direction of shift (left or right), the type of shift (circular, arithmetic, or logical), and the

amount of shift (typically 0 to n-1 bits, but sometimes 1 to n bits), where 'n' is data inputs

and data outputs of barrel shifter.

Barrel shifters are often required for performing data shifting and rotation in

many key computer operations from address decoding to computer arithmetic. Barrel

shifter circuits are essential elements in the design of data paths for DSP applications. A

significant reduction in area and power required by the barrel shifter circuit is achieved by

implementing rightward operations as operations in leftward direction. A significant

reduction in delay is possible by reducing the length of critical path.

2. Implementation of Barrel Shifter using 2:1

Multiplexer

3. Transistor Level Diagram of 2:1 Multiplexer

Fig. Transistor Level Diagram of 2:1 Multiplexer using Transmission Gate

4. Code For 4-Bit Barrel Shifter using 2:1 Multiplexer

*barrel shifter

.subckt two 1 4 5 6

.model p pmos

.model n nmos

m1 3 1 0 0 n

m2 3 1 2 2 p

m3 4 3 6 0 n

m4 6 1 4 2 p

m5 5 1 6 0 n

m6 6 3 5 2 p

vdd 2 0 dc 5v

.ends

X1 6 1 3 7 two

X2 6 2 4 8 two

X3 6 3 1 9 two

X4 6 4 2 10 two

X5 15 8 10 11 two

X6 15 9 7 12 two

X7 15 10 8 13 two

X8 15 7 9 14 two

X9 5 7 11 16 two

X10 5 8 12 17 two

X11 5 9 13 18 two

X12 5 10 14 19 two

v1 1 0 pulse(0 0 0ns 0ns 0ns 1000ns 1000ns)







.tran 0.01ns 1000ns

.plot v(1) v(2) v(3) v(4) v(5) v(6) v(15) v(16) v(17) v(18) v(19)

.end

5. OUTPUT WAVEFORMS OF BARREL SHIFTER

6. ADVANTAGES

1. Using Barrel shifter input word is either shifted left or right or remains unchanged

as per select line at a time, whereas in shift registers, data is shifted by one bit on

the rising edge of clock.

2. The propagation delay of Barrel Shifter is theoretically constant and independent

of the shift value or shifter size.

3. Barrel shifter is appropriate for smaller shifts. For larger shift values, the

logarithmic shifter becomes more effective.

7. APPLICATIONS OF BARREL SHIFTER

1. Several microprocessors incorporate it as a part of their ALU to provide fast shift

operations.

2. Barrel shifter circuits are essential elements in the design of data paths for DSP

applications.

3. Barrel shifters are often required for performing data shifting and rotation in

many key computer operations from address decoding to computer arithmetic.

4. It is used extensively in floating-point units, scalars, and multiplications by

constant numbers.

8. CONCLUSION

Each output bit of 4-bit barrel shifter can be obtained from a 2-input

multiplexer controlled by the shift-control inputs. Barrel shifter requires transmission

gates. A barrel shifter with a programmable shift-width from 0 to 3 bit to the right

supports automatic repetition of the sign bit (D3), also called sign-bit extension. It has

efficient layout. The layout size is dominated by the number of wires running through the

cell. A barrel shifter can become a stepping stone to improving computer organization

and memory.

9. BIBLIOGRAPHY

I. Digital Intergrated Circuits by Jan M. Rabaey.

II. Combinational Design Examples by John F. Wakerly.

III. Low Power VLSI Design and Technology–G. K.Yeap, F.N.Najm.

IV. VLSI Implementation of a High Performance Barrel Shifter-A paper by Abhijit

Asati and Chandrasekhar (7,November 2009)

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