Ecad &vlsi lab 18

ECAD & VLSI DESIGN
LABORATORY MANUAL
FOR
IV B.TECH ECE-I SEMESTER
MALLA REDDY COLLEGE OF ENGINEERING AND TECHNOLOGY
(An Autonomous Institution-UGC, Govt. Of India)
Department Of Electronics & Communication Engg.
Sponsored by CMR Educational Society
(Affiliated to JNTU, Hyderabad)
Maisammguda, Dhulapally
Secunderabad-500100

CONTENTS
CYCLE-I
S.NO. EXPERIMENT NAME PAGE NO.
1 Full Adder 1
2 Design Of Ripple Carry ADDER 4
3 Design Of Carry Save Adder 7
4 Design Of Carry Select Adder 10
5 BCD Adder Realization 14
6 Design of a 4 to 1 multiplexer 18
7 Array Multiplier Realization 22
8 Ripple Counters Realization-(Mod -10 & Mod-12) 27
9 Ring Counter Realization 38
10 Pseudo Random Binary Sequence Generator 41
11 Design of Accumulator 44
CYCLE-II
1 CMOS INVERTER 49
2 NAND GATE 53
3 NOR Gate 57
4 XOR GATE 60
5 CMOS 1-Bit Full Adder 64
6 Common Source Amplifier 67
7 Differential Amplifier 71

MALLA REDDY COLLEGE OF ENGINEERING AND TECHNOLOGY DEPT.OF ECE
1 | P a g e
Experiment 1: Full Adder
Aim:
Realize the full adder using Verilog.
Software Required : QuestaSim Simulator
Theory:
A combinational circuit that performs the addition of three bits is called a half-adder. This circuit needs
three binary inputs and produces two binary outputs. One of the input variables designates the augend
and other designates the addend. Mostly, the third input represents the carry from the previous lower
significant position. The output variables produce the sum and the carry.
The simplified Boolean functions of the two outputs can be obtained as
below: Sum S = x y z
Carry C = xy + xz + yz
Where x, y & z are the two input variables.
Program:
//Gate-level description of Full Adder using two Half Adder
//Description of Half Adder
module halfadder(s,co,x,y);
input x,y;
output s,co;
//Instatiate primitive
gates xor (s,x,y);
and (co,x,y);
endmodule
//Description of Full Adder
module fulladder(s,co,x,y,ci);
input x,y,ci;
output s,co;
wire s1,d1,d2; //Outputs of first XOR and AND gates
//Instantiate Half Adder halfadder ha_1(s1,d1,x,y); halfadder
ha_2(s,d2,s1,ci);
or or_gate(co,d2,d1);
endmodule
//Stimulus for testing Full Adder module simulation;

2 | P a g e
reg x,y,ci; wire s,co;
//Instantiate Full Adder fulladder fa_test(s,co,x,y,ci); initial
begin
x=1'b0; y=1'b0; ci=1'b0;
#100 x=1'b0; y=1'b0; ci=1'b1; #100 x=1'b0; y=1'b1; ci=1'b0; #100 x=1'b0;
y=1'b1; ci=1'b1; #100 x=1'b1; y=1'b0; ci=1'b0; #100 x=1'b1; y=1'b0; ci=1'b1;
#100 x=1'b1; y=1'b1; ci=1'b0; #100 x=1'b1; y=1'b1; ci=1'b1; end
endmodule
Logic Diagram:
Expected Output Waveform:

3 | P a g e
Simulation Output Waveform:
Result:
Thus the logic circuit for the Full adder is designed in Verilog HDL and the output is verified.

4 | P a g e
Experiment 2: Design Of Ripple Carry ADDER Using Verilog HDL
Aim:To Design Ripple Carry Adder using Verilog HDL
Software Required :QuestaSim Simulator
Theory:
The n-bit adder built from n one –bit full adders is known as ripple carry adder because of the
carry is computed. The addition is not complete until n-1
th
adder has computed its Sn-1 output; that
results depends upon ci input, n and so on down the line, so the critical delay path goes from the 0-bit
inputs up through ci’s to the n-1 bit.(We can find the critical path through the n-bit adder without
knowing the exact logic in the full adder because the delay through the n-bit adder without knowing the
exact logic in the full adder because the delay through the n-bit carry chain is so much longer than the
delay from a and b to s). The ripple-carry adder is area efficient and easy to design but it is when n is
large.It can also be called as cascaded full adder.
The simplified Boolean functions of the two outputs can be obtained as below:
Sum si = ai xor bi xor ci
Carry ci+1 = aibi +bi ci +ai ci
Where x, y & z are the two input variables.
Procedure:
1The full-adder circuit is designed and the Boolean function is found
out.
2.The Verilog Module Source for the circuit is written.
3.It is implemented in Model Sim and Simulated.
4.Signals are provided and Output Waveforms are viewed.
Circuit diagram:

5 | P a g e
Ripple carry adder using verilog code:
module ripplecarryadder(s,cout,a,b,cin); output[7:0]s;
output cout; input[7:0]a,b; input cin;
wire c1,c2,c3,c4,c5,c6,c7; fulladd fa0(s[0],c1,a[0],b[0],cin); fulladd
fa1(s[1],c2,a[1],b[1],c1); fulladd fa2(s[2],c3,a[2],b[2],c2); fulladd
fa7(s[7],cout,a[7],b[7],c7);
endmodule
module fulladd(s,cout,a,b,cin); output s,cout;
input a,b,cin;
wire s1,c1,c2;
xor(s1,a,b);
xor(s,s1,cin);
and(c1,a,b);
and(c2,s1,cin);
xor(cout,c2,c1);
endmodule
Waveform of ripple carry adder:

6 | P a g e
Test bench wave form of Ripple carry adder:
RESULT:
Thus the logic circuit for the Ripple carry adder is designed in Verilog HDL and the output is
verified.

7 | P a g e
Experiment 3: Design Of Carry Save Adder Using Verilog HDL
Aim:
To design Carry Save Adder using Verilog HDL
Theory:
Carry save adders are suitable when three or more operands are to be
added, as in some multiplication schemes. In this adder a separate sum and
carry bit is generated for partial results , except when the last operand is
added. For example, when three numbers are added, the first two are added
using a carry save adder. The partial result is two numbers corresponding to
the sum and the carry .The last operand is added using a second carry save
adder stage. The results become the sum and carry numbers. Thus a carry save
adder reduces the number of operands by one for each adder stage. Finally the
sum and carry are added using an adder with carry propagation- for example
carry look ahead adder.
Procedure;
1. The carry save adder is designed.
2. The Verilog program source code for the circuit is written.
3. It is implemented in Model Sim and Simulated.
4. Signals are provided and Output Waveforms are viewed.
Carry save adder using Verilog:
module
carrysaveadder(
d,a,b,e); output
[4:0]d;
input e;
input [3:0]a,b;

8 | P a g e
wire s1,s2,s3,c0,c1,c2,c3,c4,c5,c6,c7;
fulladder
a1(d[0],c7,a[0],b[0]
,e); fulladder
a2(s3,c6,a[1],b[1],e
);
fulladder a3(s2,c5,a[2],b[2],e); fulladder a4(s1,c4,a[3],b[3],e); fulladder
a5(d[1],c3,c7,s3,e); fulladder a6(d[2],c2,c6,c3,s2); fulladder
a7(d[3],c1,c5,s1,c2); fulladder a8(d[4],c0,c4,c1,e); endmodule
module fulladder(s,c, x,y,z); output s,c;
input x,y,z; xor (s,x,y,z);
assign c = ((x & y )|(y & z)|( z & x)) ; endmodule
Logic Diagram:

9 | P a g e
Waveform carry save adder:
Test bench waveform carry-save adder:
RESULT:
Thus the logic circuit for the carry save adder is designed in Verilog HDL and the output is
verified.

10 | P a g e
Experiment 4: Design Of Carry Select Adder Using Verilog HDL
Aim:To design a Carry Select Adder using Verilog HDL
Theory:
Carry-select adders use multiple narrow adders to create fast wide
adders. A carry-select adder provides two separate adders for the upper
words, one for each possibility. A MUX is then used to select the valid
result. Consider an 8-bit adder that is split into two 4-bit groups. The
lower-order bits and are fed into the 4_bit adder l to produce the sum
bits and a carry-out bit .the higher order bits and are used as
input to one 4_bit adder and and are used as input of the
another 4_bit adder. Adder U0 calculates the sum with a carry-in of
C3=0.while U1 does the same only it has a carry-in value of C3=1.both
sets of results are used as inputs to an array of 2:1 MUXes .the carry bit
from the adder L is used as the MUX select signal. If =0 then the results
U0 are sent to the output, while a value of =1 selects the results of
U1 for . The carry-out bit is also selected by the MUX array.
Procedure:
1. The carry-select adder circuit is designed and the Boolean function is found out.
2. The Verilog Module Source for the circuit is written.
carry-select adder using verilog:

11 | P a g e
fulladder f1(s[0],c0,x[0],y[0],z);
fulladder f2(s[1],c1,x[1],y[1],c0);
fulladder f5(s4,c4,x[4],y[4],c3);
fulladder f9(s8,c8,x[8],y[8],~c3);
muxer mu1(m[1],s4,s8,c3);
muxer mu5(m[5],c7,c11,c3);
endmodule
module fulladder (s,c,x,y,z); output s,c;
input x,y,z; xor (s,x,y,z);
assign c = ((x & y) | (y & z) | (z & x));
endmodule
module muxer (m,s1,s2,c);
output m;
input s1,s2,c;
wire f,g,h; not (f,c);
and (g,s1,c); and (h,s2,f);
or (m,g,h);
endmodule

12 | P a g e
Logic Diagram:

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Waveform of carry-select adder:
Test bench waveform of carry-select adder:
RESULT:
Thus the logic circuit for the carry select adder is designed in Verilog HDL and the output is verified.

14 | P a g e
Experiment 5: BCD Adder Realization In Verilog HDL
Aim:
To design a BCD adder circuit using Verilog HDL
Software Required: QuestaSim Simulator
Theory:
A BCD adder is the circuit that adds two BCD digits in parallel and produces a sum digit also in
BCD. The input digit does not exceed 9,the output sum cannot greater than 9+9+1=19, the 1 in the sum
being an input carry. Suppose we apply two decimal digits, together with the input carry, are first added
in the top 4-bit binary adder to produce the binary sum. When the output carry is equal to zero, nothing
is added in the binary sum . When it is equal to one, binary 0110 is added to binary sum through the
bottom 4-bit binary adder. Output generated from bottom binary adder can be ignored.
The output carry can be expressed in Boolean function
k = c4 + s3s2 + s3s1
Procedure:
1. The BCD adder circuit is designed and the Boolean function is found out.
2. The VHDL program source code for the circuit is written.
Bcd adder using Verilog :
module
bcdadder(s,k,a,b,c,d,e);
output [4:7] s;
inout k;
input [0:3]a,b;
input c,d,e;
wire c1,c2,c3,c4,s0,s1,s2,s3,e1,e2,e3,e4;
fulladder f1(s0,c1,a[0],b[0],c);
fulladder f2(s1,c2,a[1],b[1],c1);

15 | P a g e
assign k=((s3 & s2) | (s3 & s1)| c4);
fulladder f5(s[4],e1,s0,d,e);
fulladder f6(s[5],e2,s1,k,e1);
fulladder f7(s[6],e3,s2,k,e2);
fulladder f8(s[7],e4,s3,d,e3);
endmodule
module fulladder(s,ca,a,b,c); output
s,ca;
input a,b,c;
xor(s,a,b,c);
assign ca=((a & b)|(b & c)| (c & a));
endmodule
Logic Diagram:
b3 a3 c3 b2 a2 c2 b1 a1 c1 b0 a0 c
c4
FA4 FA3 FA2 FA1
k s3
s2 s1 s0
d=0 e3 k e2 k e1 d=0 e=0
FA8 FA7 FA6 FA5
s7 s6 s5 s4

16 | P a g e
Waveform:
Simulation output:

17 | P a g e
Simulation output of BCD Adder
Result: The BCD adder circuit using Verilog HDL has been simulated.

18 | P a g e
Experiment 6: Design of Multiplexers
Aim: Design a 4 to 1 multiplexer circuit in Verilog.
Theory:
A digital multiplexer is a combinational circuit that selects binary information from one
of many input lines and directs it to a single output line. Multiplexing means transmitting a
large number of information units over a smaller number of channels or lines. The selection of
a particular input line is controlled by a set of selection lines. Normally, there are 2
n
input lines
and n selection lines whose bit combinations determine which input is selected. A multiplexer
is also called a data selector, since it selects one of many inputs and steers the binary
information to the output lines. Multiplexer ICs may have an enable input to control the
operation of the unit. When the enable input is in a given binary state (the disable state), the
outputs are disabled, and when it is in the other state (the enable state), the circuit functions
as normal multiplexer. The enable input (sometimes called strobe) can be used to expand two
or more multiplexer ICs to digital multiplexers with a larger number of inputs.
The size of the multiplexer is specified by the number 2
n
of its input lines and the single output
line. In general, a 2
n
– to – 1 line multiplexer is constructed from an n – to 2
n
decoder by
adding to it 2
n
input lines, one to each AND gate. The outputs of the AND gates are applied to
a single OR gate to provide the 1 – line output.
Procedure:
1. The multiplexer circuit is designed and the Boolean function is found out.
Truth table:
INPUT OUTPUT
s[1] s[0] y
0 0 D[0]
0 1 D[1]
1 0 D[2]
1 1 D[3]

19 | P a g e
Logic Diagram:
4 to 1 Multiplexer:
Multiplexer using verilog code: module multiplexer(y,d,s); output y;
input [3:0] d; input [1:0] s; wire a,b,c,e,f,g,h,i;
//Instantiate Primitive gates not (a,s[1]);
not (b,s[0]); and (c,d[0],b,a);
and (e,d[1],s[0],a); and (f,d[2],b,s[1]);
and (g,d[3],s[0],s[1]); or (h,c,e);
or (i,f,g); or (y,h,i); endmodule
//Stimulus for testing 4 to 1 Multiplexer
module simulation;
reg [3:0]d; reg [1:0]s; wire y;
//Instantiate the 4 to 1 Multiplexer multiplexer mux_t(y,d,s);

20 | P a g e
initial begin
s=2'b00;d[0]=1'b1;d[1]= 1'b0;d[2]= 1'b0;d[3]= 1'b0; #100
s=2'b00;d[0]= 1'b0;d[1]= 1'b1;d[2]= 1'b1;d[3]= 1'b1; #100
s=2'b01;d[0]= 1'b0;d[1]= 1'b1;d[2]= 1'b0;d[3]= 1'b0; #100
s=2'b01;d[0]= 1'b1;d[1]= 1'b0;d[2]= 1'b1;d[3]= 1'b1; #100
s=2'b10;d[0]= 1'b0;d[1]= 1'b0;d[2]= 1'b1;d[3]= 1'b0; #100
s=2'b10;d[0]= 1'b1;d[1]= 1'b1;d[2]= 1'b0;d[3]= 1'b1; #100
s=2'b11;d[0]= 1'b0;d[1]= 1'b0;d[2]= 1'b0;d[3]= 1'b1; #100
s=2'b11;d[0]= 1'b1;d[1]= 1'b1;d[2]= 1'b1;d[3]= 1'b0; end
endmodule
Waveform:

21 | P a g e
Waveform of multiplexers
Test bench waveform of multiplexers:
RESULT:
Thus the multiplexer is designed in Verilog HDL and the output is verified.

22 | P a g e
Experiment 7: Array Multiplier Realization In Verilog Hdl
Aim:
To design an array multiplier circuit for 4 inputs and 8 outputs using VHDL.
Theory:
Binary multiplication can be accomplished by several approaches. The approach presented
here is realized entirely with combinational circuits. Such a circuit is called an array
multiplier.The term array is used to describe the multiplier because the multiplier is
organized as an array structure. Each row, called a partial product, is formed by a bit-by-bit
multiplication of each operand.For example, a partial product is formed when each bit of
operand ‘a’ is multiplied by b0, resulting in a3b0, a2b0,a1b0, a0b0. The binary
multiplication table is identical to the AND truth table.Each product bit {o(x)}, is formed by
adding partial product columns. The product equations, including the carry-in {c(x)}, from
column c(x-1), are (the plus sign indicates addition not OR).Each product term, p(x), is
formed by AND gates and collection of product terms needed for the multiplier. By adding
appropriate p term outputs, the multiplier output equations are realized, as shown in
figure.
4X 4 Array Multiplier:
a3 a2 a1 a0
b3 b2 b1 b0
a3b0 a2b0 a1b0 a0b0
a3b1 a2b1 a1b1 a0b1
a3b2 a2b2 a1b2 a0b2
a3b3 a2b3 a1b3 a0b3
o7 o6 o5 o4 o3 o2 o1
a0b0 = p0 a1b2 = p8
a1b0 = p1 a0b3 = p9
a0b1 = p2 a3b1 = p10
a2b0 = p3 a2b2 = p11

23 | P a g e
a1b1 = p4 a1b3 = p12
a0b2 = p5 a3b2 = p13
a3b0 = p6 a2b3 = p14
a2b1 = p7 a3b3 = p15
Truth Table:
A B A X B
0 0 0
0 1 0
1 0 0
1 1 1
Program:
module mmmm(m,a,b);
input [3:0]a; input [3:0]b; output [7:0]m; wire [15:0]p; wire
[12:1]s; wire [12:1]c;
and(p[0],a[0],b[0]);
and(p[1],a[1],b[0]);
and(p[2],a[0],b[1]);
and(p[3],a[2],b[0]);
and(p[4],a[1],b[1]);
and(p[5],a[0],b[2]);
and(p[6],a[3],b[0]);
and(p[7],a[2],b[1]);
and(p[8],a[1],b[2]);
and(p[9],a[0],b[3]);

24 | P a g e
and(p[10],a[3],b[1]);
and(p[11],a[2],b[2]);
and(p[12],a[1],b[3]);
and(p[13],a[3],b[2]);
and(p[14],a[2],b[3]);
and(p[15],a[3],b[3]);
half ha1(s[1],c[1],p[1],p[2]); half ha2(s[2],c[2],p[4],p[3]); half ha3(s[3],c[3],p[7],p[6]);
full fa4(s[4],c[4],p[11],p[10],c[3]); full fa5(s[5],c[5],p[14],p[13],c[4]); full
fa6(s[6],c[6],p[5],s[2],c[1]); full fa7(s[7],c[7],p[8],s[3],c[2]); full
fa8(s[8],c[8],p[12],s[4],c[7]); full fa9(s[9],c[9],p[9],s[7],c[6]);
half ha10(s[10],c[10],s[8],c[9]);
full fa11(s[11],c[11],s[5],c[8],c[10]); full fa12(s[12],c[12],p[15],s[5],c[11]);
buf(m[0],p[0]);
buf(m[1],s[1]);
buf(m[2],s[6]);
buf(m[3],s[9]);
buf(m[4],s[10]);
buf(m[5],s[11]);
buf(m[6],s[12]);
buf(m[7],c[12]);
endmodule
module half(s,co,x,y); input x,y;
output s,co;
//Instatiate primitive gates xor (s,x,y);
and (co,x,y); endmodule
//Description of Full Adder module full(s,co,x,y,ci); input x,y,ci;
output s,co;
wire s1,d1,d2; //Outputs of first XOR and AND gates //Instantiate Half Adder
half ha_1(s1,d1,x,y); half ha_2(s,d2,s1,ci); or or_gate(co,d2,d1);
endmodule

25 | P a g e
Logic Diagram:
P14 P13
P15 P11,P10 P7 P6 P4 P3 P2 P1 P0
FA FA HA HA HA
P12 P8
FA FA FA
P9
FA FA FA HA
O7 O6 O5 O4 O3 O2 O1 O0

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Wave Form:
RESULT:
Thus an array multiplier circuit for 4 inputs and 8 outputs using VHDL is designed and the output is
verified.

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Experiment 8: Ripple Counter Realization In Verilog HDL
Aim:
To realize an asynchronous ripple counter in Verilog
Theory:
In a ripple counter, the flip-flop output transition serves as a source for triggering other
flip-flops. In other words, the Clock Pulse inputs of all flip-flops (except the first) are triggered not by the
incoming pulses, but rather by the transition that occurs in other flip-flops. A binary ripple counter
consists of a series connection of complementing flip-flops (JK or T type), with the output of each flip-
flop connected to the Clock Pulse input of the next higher-order flip-flop. The flip-flop holding the LSB
receives the incoming count pulses. All J and K inputs are equal to 1. The small circle in the Clock Pulse
/Count Pulse indicates that the flip-flop complements during a negative-going transition or when the
output to which it is connected goes from 1 to 0. The flip-flops change one at a time in rapid succession,
and the signal propagates through the counter in a ripple fashion. A binary counter with reverse count is
called a binary down-counter. In binary down-counter, the binary count is decremented by 1 with every
input count pulse.
Procedure:
1. The 4 bit asynchronous ripple counter circuit is designed.
//Structural description of Ripple Counter
module ripplecounter(A0,A1,A2,A3,COUNT,RESET);
output A0,A1,A2,A3;
input COUNT,RESET;
//Instantiate Flip-Flop
FF F0(A0,COUNT,RESET); FF
F1(A1,A0,RESET);
FF F2(A2,A1,RESET);
FF F3(A3,A2,RESET);
endmodule

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//Description of Flip-Flop
module FF(Q,CLK,RESET); output Q;
input CLK,RESET; reg Q;
always @(negedge CLK or negedge RESET) if(~RESET)
Q=1'b0; else
Q=(~Q); endmodule
//Stimulus for testing Ripple Counter
module simulation; reg COUNT;
reg RESET;
wire A0,A1,A2,A3;
//Instantiate Ripple Counter
ripplecounter rc_t(A0,A1,A2,A3,COUNT,RESET); always
#5 COUNT=~COUNT; initial
begin
COUNT=1'b0;
RESET=1'b0; #10 RESET=1'b1; end
endmodule
LOGIC DIAGRAM:
4-Bit Ripple Counter:

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TRUTH TABLE:
COUNT A0 A1 A2 A3
0 0 0 0 0
1 1 0 0 0
2 0 1 0 0
3 1 1 0 0
4 0 0 1 0
5 1 0 1 0
6 0 1 1 0
7 1 1 1 0
8 0 0 0 1
9 1 0 0 1
10 0 1 0 1
11 1 1 0 1
12 0 0 1 1
13 1 0 1 1
14 0 1 1 1
15 1 1 1 1

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Waveform of ripple counter:
Testbenchwaveform of ripple counter:

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LOGIC DIAGRAM:
MOD-10 Ripple Counter:

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TRUTH TABLE:
COUNT A0 A1 A2 A3
0 0 0 0 0
1 1 0 0 0
2 0 1 0 0
3 1 1 0 0
4 0 0 1 0
5 1 0 1 0
6 0 1 1 0
7 1 1 1 0
8 0 0 0 1
9 1 0 0 1
10 0 0 0 0
/Structural description of MOD10 Counter
module MOD10(A0,A1,A2,A3,COUNT); output
A0,A1,A2,A3;
input COUNT;
wire RESET;
FF F0(A0,COUNT,RESET); FF
F1(A1,A0,RESET);
FF F2(A2,A1,RESET);
FF F3(A3,A2,RESET);
//Instantiate Primitive gate
nand (RESET,A1,A3);
endmodule
module FF(Q,CLK,RESET);
output Q;

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input CLK,RESET;
reg Q=1'b0;
always @(negedge CLK or negedge RESET)
if(~RESET)
Q=1'b0;
else
Q=(~Q);
endmodule
//Stimulus for testing MOD10 Counter module simulation;
reg COUNT;
wire A0,A1,A2,A3;
//Instantiate MOD10 Counter
MOD10 MOD10_TEST(A0,A1,A2,A3,COUNT); always
begin
COUNT=1'b0; end
Endmodule
Waveform of mod 10 Counter:

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Testbenchwaveform of mod 10:
LOGIC DIAGRAM:
MOD-12 Ripple Counter:

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TRUTH TABLE:
COUNT A0 A1 A2 A3
0 0 0 0 0
1 1 0 0 0
2 0 1 0 0
3 1 1 0 0
4 0 0 1 0
5 1 0 1 0
6 0 1 1 0
7 1 1 1 0
8 0 0 0 1
9 1 0 0 1
10 0 1 0 1
11 1 1 0 1
12 0 0 0 0

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//Structural description of MOD12 Counter
module MOD12(A0,A1,A2,A3,COUNT); output A0,A1,A2,A3;
input COUNT; wire RESET;
FF F0(A0,COUNT,RESET); FF F1(A1,A0,RESET);
FF F2(A2,A1,RESET);
FF F3(A3,A2,RESET);
//Instantiate Primitive gates nand (RESET,A2,A3); endmodule
module FF(Q,CLK,RESET); output Q;
input CLK,RESET; reg Q=1'b0;
always @(negedge CLK or negedge RESET) if(~RESET)
Q=1'b0; else
Q=(~Q); endmodule
//Stimulus for testing MOD12 Counter
module simulation; reg COUNT;
wire A0,A1,A2,A3;
//Instantiate MOD12 Counter
MOD12 MOD12_TEST(A0,A1,A2,A3,COUNT); always
begin
COUNT=1'b0; end endmodule

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Waveform of mod 12 counter :
Testbenchwaveform of mod 12 counter:
RESULT:
Thus the ripple counter is designed in Verilog HDL and the output is verified.

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Experiment 9: Ring Counter Realization In Verilog HDL
AIM:
To realize a ring counter in Verilog and VHDL.
Theory:
A ring counter is a circular shift register with only one flip-flop being set at ay particular time; all
others are cleared. The single bit is shifted from one flip-flop tot the other to produced the
sequence of timing signals.
Procedure:
1. The 4 bit ring counter circuit is designed.
Binary Ring Counter Design in Verilog
module my_ringcntvlog (q,clk,reset);
output [0 : 3]q;
input clk,reset;
reg [0 : 3] q;
always @ (negedge clk or reset)
begin
if (~reset)
q = 4'b 1000;
else if (reset)
begin
q[0] <= q[3];
q[1] <= q[0];
q[2] <= q[1];
q[3] <= q[2];
end
end
endmodule

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Logic Diagram:
Truth Table:
Waveforms

40 | P a g e
Waveform of ring counter:
Test bench waveform of ring counter:
RESULT:
Thus the ring counter is designed in Verilog HDL and the output is verified.

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Experiment 10: Pseudo Random Binary Sequence Generator
Aim:
Realize the Pseudo random binary sequence generator in Verilog HDL
Theory:
Random numbers for polynomial equations are generated by using the shift register circuit. The random
number generator is nothing but the Linear Feedback Shift Register(LFSR). The shift registers are very
helpful and versatile modules that facilitate the design of many sequential circuits whose design may
otherwise appear very complex. In its simplest form, a shift register consists of a series of flip-flops
having identical interconnection between two adjacent flip-flops. Two such registers are shift right
registers and the shift left registers. In the shift right register, the bits stored in the flip-flops shift to the
right when shift pulse is active. Like that, for a shift left register, the bits stored in the flip-flops shift left
when shift pulse is active. In the shift registers, specific patterns are shifted through the register. There
are applications where instead of specific patterns, random patterns are more important. Shioft
registers can also built to generate such patterns , which are pseudorandom in nature. Called Linear
Feedback Shift Registers (LFSR’s), these are very useful for encoding and decoding the error control
codes. LFSRs used as a generators of pseudorandom sequences have proved externally useful in the area
of testing of VLSI chips.
Circuit diagram:

42 | P a g e
module psrno(y,clk);
output y;
input clk;
wire [1:0]q;
wire a;
dff df1(q[0],a,clk);
dff df2(q[1],q[0],clk);
dff df3(y,q[1],clk);
xor x1(a,y,q[1]);
endmodule
module dff(q,d,clk);
output q;
input d,clk;
reg q=0;
always @(posedge clk)
begin
q = d;
end
endmodule
Waveform of prbs:

43 | P a g e
Testbenchwaveform of prbs :
RESULT:
Thus the pseudo random binary generator is designed in Verilog HDL and the output is verified.

44 | P a g e
Experiment 11: Design of Accumulator
Aim:
Realize the accumulator in Verilog HDL
Theory:
An accumulator differs from a counter in the nature of the operands of the add and subtract
operation:
•In a counter, the destination and first operand is a signal or variable and the other operand
is a constant equal to 1: A <= A + 1.
•In an accumulator, the destination and first operand is a signal or variable, and the second
operand is either:
♦ A signal or variable: A <= A + B
♦ A constant not equal to 1: A <= A + Constant
An inferred accumulator can be up, down or updown. For an updown accumulator, the
accumulated data may differ between the up and down mode:
...
if updown = '1' then a <= a + b;
else
a <= a - c;
Program:
module accum (C, CLR, D, Q); input C, CLR;
input [3:0] D; output [3:0]
Q; reg [3:0] tmp;
always @(posedge C or posedge CLR) begin
if (CLR)
tmp = 4'b0000;
else
tmp = tmp + D; end
assign Q = tmp; endmodule

45 | P a g e
Logic Diagram:
Circuit diagram:

46 | P a g e
Wave form of accumulator :
Testbench waveform of accumulator:
RESULT:
Thus the logic circuit for the Accumulator is designed in Verilog HDL and the output is
verified.

47 | P a g e
CYCLE-II

48 | P a g e
Preface: Introduction to ASIC Design Flow: Typical ASIC Design Flow by Using Mentor Graphics Tools is
given below.
Pyxis Schematic:
Pyxis Schematic: Pyxis Schematic interacts seamlessly with other solutions in the Pyxis Custom IC Design
Platform to create, develop, simulate, verify, optimize and implement even the most challenging full custom
analog and mixed-signal IC designs quickly and accurately—the first time. As a designer, you enjoy a
consistent look and feel in single environment, whether creating schematics, block diagrams, symbols, or HDL
representations. Additionally, Mentor’s foundry partners provide certified design kits for use with Pyxis
Custom IC Design Platform solutions.
Pyxis Layout: Pyxis Layout supports an extensive set of editing functions for efficient, accurate polygon
editing. This gives the design engineer full control of circuit density and performance, while improving
productivity by as much as 5X. Hierarchy and advanced window management allows multiple views of the
same cell and provides the capability to edit both views. Additionally, design engineers can create matched
analog layouts quickly by editing using a half-cell methodology. Calibre: Debugging the error results of
physical and circuit verification is costly, both in time and resources. Calibre RVE provides fast, flexible, easy-
to-use graphical debugging capabilities that minimize your turnaround time and get you to “tapeout-clean”
on schedule. Better yet, Calibre RVE easily integrates into all popular layout environments, so no matter
which design environment you use, Calibre RVE provides the debugging technology you need for fast,
accurate error resolution.

49 | P a g e
Experiment I: Design and Implementation of an Inverter
AIM: To design and Implementation of an Inverter
TOOLS: Mentor Graphics: Pyxis Schematic, Pyxis Layout, Eldo, Ezwave, Calibre
Theory:
The inverter is universally accepted as the most basic logic gate doing a Boolean operation on a single input
variable. Fig.1 depicts the symbol, truth table and a general structure of a CMOS inverter. As shown, the
simple structure consists of a combination of an pMOS transistor at the top and a nMOS transistor at the
bottom.CMOS is also sometimes referred to as complementary-symmetry metal–oxide–semiconductor. The
words "complementary-symmetry" refer to the fact that the typical digital design style with CMOS uses
complementary and symmetrical pairs of p-type and n-type metal oxide semiconductor field effect transistors
(MOSFETs) for logic functions. Two important characteristics of CMOS devices are high noise immunity and
low static power consumption. Significant power is only drawn while the transistors in the CMOS device are
switching between on and off states. Consequently, CMOS devices do not produce as much waste heat as
other forms of logic, for example transistor-transistor logic (TTL) or NMOS logic, which uses all n-channel
devices without p-channel devices.
Schematic
Capture:

50 | P a g e
Procedure:
1. Connect the Circuit as shown in the circuit diagram using Pyxis Schematic tool
2. Enter into Simulation mode.
3. Setup the Analysis and library.
4. Setup the required analysis.
5. Probe the required Voltages
6. Run the simulation.
7. Observe the waveforms in EZ wave.
8. Draw the layout using Pysis Layout.
9. Perform Routing using IRoute
10. Perform DRC, LVS, PEX.
Schematic Symbol:

51 | P a g e
Testing the Schematic:
Simulation Output:
Input Vs Output
Transient and DC
Characteristics:

52 | P a g e
Layout of the Inverter:

53 | P a g e
Experiment II: NAND GATE
Aim: To create a library and build a schematic of a NAND GATE, to create a symbol for the Inverter, To build
an Inverter Test circuit using your Inverter, To set up and run simulations on the Inverter_Test design.
EDA Tool: Mentor Graphics
Schematic :

54 | P a g e
PROCEDURE:
1. Connect the Circuit as shown in the circuit diagram using Pyxis schematic.
2. Create a simulation schematic for simulation.
3. Add necessary nets in outputs to view waveforms.
4. Run the Simulation and observe results in EZwave.
5. Draw the Layout for the circuit using Pyxis Layout.
7. Run the physical verification (DRC, LVS, PEX) using Calibre tool .
8. Run the post layout simulation by adding the .dspf file generated in PEX.
9. Observe the post layout results.
Symbol Creation:

55 | P a g e
Building the NAND Test Design
Creating a layout view of NAND gate

56 | P a g e
Simulation Output:

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EXPERIMENT NO III: NOR Gate
AIM: To design and simulate the CMOS NOR gate
TOOLS: Mentor Graphics: Pyxis Schematic, Pyxis Layout, Eldo, Ezwave, Calibre
CIRCUIT DIAGRAM:

58 | P a g e
SIMULATION CIRCUIT:
PROCEDURE:

59 | P a g e
Simulation Output:
Layout:

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EXPERIMENT NO IV: XOR GATE
Aim: To create a library and build a schematic of an XOR gate, to create a symbol for the XOR, To build an
Inverter Test circuit using your XOR, To set up and run simulations on the XOR_Test design.
EDA Tools: Pyxis Schematic, Pyxis Layout, Eldo, Ezwave, Calibre
PROCEDURE:

61 | P a g e
Symbol Creation
Building the XOR Gate Test Design

62 | P a g e
PROCEDURE:
9. Observe the post layout results
Simulation output:

63 | P a g e
Layout:

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EXPERIMENT NO V: CMOS 1-Bit Full Adder
AIM: To design and simulate the CMOS 1 Bit Full Adder.
TOOLS: Pyxis Schematic, Pyxis Layout, Eldo, Ezwave, Calibre.
Schematic Diagram:
PROCEDURE:
9. Observe the post layout results

65 | P a g e
Testing the Full Adder:
Layout:

66 | P a g e
Simulation Output:

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EXPERIMENT NO VI: Common Source Amplifier
AIM: To design and simulate the Common Source Amplifier.
Circuit Diagram:

68 | P a g e
Simulation Circuit:
PROCEDURE:

69 | P a g e
AC Analysis:
Transient Analysis result:

70 | P a g e
Layout:

71 | P a g e
EXPERIMENT NO VII: Differential Amplifier
AIM: To design and simulate the Differential Amplifier.
CIRCUIT DIAGRAM:

72 | P a g e
Simulation Circuit:
PROCEDURE:

73 | P a g e
RESULTS:
AC Analysis result:

74 | P a g e
Transient Analysis
Result:

Ecad &vlsi lab 18

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