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Unit -2
Digital Circuits Design
Combinational Logic Design; Adders, Subtractor, Multiplier, Multiplexers,
Demultiplexers, Decoders, Encoders, Code Converters.
Sequential Logic Design- Flip-Flops, Registers, Counters, Finite State
Machines-Mealy and Moore type, Serial Adder
CO2 : Discuss about the different combinational and sequential logic blocks. (K3)
Combinational Vs Sequential Circuits
Combinational Circuit
Sequential Circuit
Design Flow
Logic Diagram
Expression
Truth Table
Binary Adder
1-bit Adder
N-bit Adder
1 bit adder without carry (A+B) [Half Adder]
1 bit adder with carry (A+B+Cin) [Full Adder]
2 bit Adder [A1A0 + B1B0]
4 bit Adder [A3A2A1A0 + B3B2B1B0]
Example:
• Ripple Carry Adder
• BCD Adder
Half Adder
Full Adder
Full Adder
Half Subtractor
Full Subtractor
Full Subtractor
Parallel Adder
4-bit Ripple Carry Addition: Example
C0
FA
A0
S0
B0
FA
A1
S1
B1
FA
A2
S2
B2
FA
A3
S3
B3
C4 C1
C2
C3
T=1 0
0 1
0 1
0 0
1
0
0 1
0 0
1 1
1
0
0
0 0
0 0
0 0
0
T=0
B=0101
A=0011
S=0000
S=0110
0
0 1
0 0
1 0
1
T=2 S=0100
0
0 0
1 0
1 0
1
T=3 S=0000
1
0 0
1 0
1 0
1
T=4 S=1000
Carry Look Ahead Adder
Carry-Look Ahead Adder
Propagate
Propagate
Generate
Generate
Inputs Outputs
ci ai bi si ci+1
0 0 0 0 0
0 0 1 1 0
0 1 0 1 0
0 1 1 0 1
1 0 0 1 0
1 0 1 0 1
1 1 0 0 1
1 1 1 1 1
Carry-Look Ahead Adder
Gi = AiBi
Pi = Ai ⊕Bi
Gi is known as the carry Generate signal
Pi is known as the carry propagate signal
Si = Pi ⊕ Ci
Ci+1 = Gi + PiCi
Carry-Look Ahead Adder
Si = Pi ⊕ Ci Ci+1= Gi + PiCi
C1= G0 + P0C0
C2= G1 + P1C1
C3= G2 + P2C2
C4= G3 + P3C3
S0= P0 ⊕ C0
S1= P1 ⊕ C1
S2= P2 ⊕ C2
S3= P3 ⊕ C3
Gi= Ai . Bi
G0 = A0 .B0
G1 = A1 .B1
G2 = A2 .B2
G3 = A3 .B3
Pi= Ai ⊕ Bi
P0 = A0 ⊕ B0
P1 = A1 ⊕ B1
P2 = A2 ⊕ B2
P3 = A3 ⊕ B3
c1 = G0 + P0c0
c2 = G1 + P1c1
c2 = G1 + P1(G0 + P0c0)
c2 = G1 + P1G0 + P1P0c0
c3 = G2 + P2c2
c3 = G2 + P2(G1 + P1G0 + P1P0c0)
c3 = G2 + P2G1 + P2P1G0 + P2P1P0c0
c4 = G3 + P3G2 + P3P2G1 + P3P2P1G0 + P3P2P1P0c0
Gi = ai . bi (generate)
Pi = ai ⊕ bi (propagate)
Gi/Pi function of inputs only
Carry-Look Ahead Adder
C1 = G0 + P0C0
C2 = G1 + P1C1 = G1 + P1 (G0 + P0C0) = G1 + P1G0 + P1P0C0
C3 = G2 + P2C2 = G2 + P2G1 + P2P1G0 + P2P1P0C0
C4 = G3 + P3C3 = G3 + P3G2 + P3P2G1 + P3P2P1G0 + P3P2P1P0C0
Carry-Look
Ahead Adder
BCD Adder
BCD Adder
Sum Sum > 9
S3 S2 S1 S0 Y
0 0 0 0 0
0 0 0 1 0
0 0 1 0 0
0 0 1 1 0
0 1 0 0 0
0 1 0 1 0
0 1 1 0 0
0 1 1 1 0
1 0 0 0 0
1 0 0 1 0
1 0 1 0 1
1 0 1 1 1
1 1 0 0 1
1 1 0 1 1
1 1 1 0 1
1 1 1 1 1
Number > 9
BCD Adder
Sum > 9
BCD Adder
0000 (Sum <9)
0110 (Sum >9)
BCD Adder
Signed Parallell Adder
Binary multiplier
Two-bit by two-bit binary multiplier
Binary multiplier
Four-bit by three-bit binary multiplier
Magnitude Comparator
A>B: AB'
A<B: A'B
A=B: A'B' + AB
Magnitude Comparator
Magnitude Comparator [2 bit]
Magnitude Comparator [2 bit]
A>B: A1B1’ + A0B1’B0’ + A1A0B0’
A=B: A1’A0’B1’B0’ + A1’A0B1’B0 +
A1A0B1B0 + A1A0’B1B0’
Magnitude Comparator [2 bit]
A<B:A1’B1 + A0’B1B0 + A1’A0’B0
Magnitude Comparator [2 bit]
Multiplexer
Multiplexer
• A MUX is a digital switch that has
multiple inputs (sources) and a single
output (destination).
• The select lines determine which input
is connected to the output.
• MUX Types
 2-to-1 (1 select line)
 4-to-1 (2 select lines)
 8-to-1 (3 select lines)
 16-to-1 (4 select lines)
Select Lines
Inputs
(sources)
Output
(destination)
1
2N
N
MUX
Multiplexer [2:1]
S Output
0 I0
1 I1
Multiplexer [4:1]
S1 S0 Y
0 0 I0
0 1 I1
1 0 I2
1 1 I3
Implement AND gate using 2:1 MUX
Implement OR gate using 2:1 MUX
Implement 4:1 MUX using 2:1 MUX
S1 S0 Y
0 0 I0
0 1 I1
1 0 I2
1 1 I3
Implement f(a, b, c) = a’b’c + ab using 8:1 MUX
Canonical Form :
Implement f(a, b, c) = a’b’c + ab using 4:1 MUX
f ( A, B, C) = Σ ( 1, 2, 3, 5, 6 ) with don’t care (7) using
4 : 1 MUX with AB as select lines
f ( A, B, C) = Σ ( 1, 2, 3, 5, 6 ) with don’t care (7) using
4 : 1 MUX with AC as select lines
Demultiplexer
Demultiplexer
Demultiplexer: 1:8 using 4:1
Encoder
An encoder is a circuit that accepts many inputs and generates the output
in a coded form. Encoder is a device which has 2n' inputs and 'n' numberof
output
• Adecoder is a combinational circuit.
• A decoder accepts a set of inputs that represents a binary number and
activates only that output corresponding to the input number.All other
outputs remain inactive.
• There are 2N possible input combinations, for each of these input
combination only one output will be HIGH (active) all other outputs are
LOW
• Some decoder have one or more ENABLE (E) inputs that are used to control
the operation of decoder.
Decoder
BLOCK DIAGRAM OF DECODER
DECODER
A0
A1
A2
AN-1
.
.
.
.
N- Inputs M- Outputs
Only one output is High for
each input
.
.
.
.
B0
B1
B2
BM-1
2 to 4 Line Decoder:
 Block diagram of 2 to 4 decoder is shown in fig.
 Aand B are the inputs. ( No. of inputs =2)
 No. of possible input combinations: 22=4
 No. of Outputs : 22=4, they are indicated by D0, D1, D2 and D3
 From the Truth Table it is clear that each output is “1” for only specific
combination of inputs.
A
B
0
D
D1
D2
3
2 X 4
Decoder
INPUTS OUTPUTS
A B D0 D1 D2 D3
0 0 1 0 0 0
0 1 0 1 0 0
1 0 0 0 1 0
1 1 0 0 0 1
TRUTH TABLE
Inputs
D
Outputs
BOOLEAN EXPRESSION:
From Truth Table
D0 A B
D2 A B
LOGIC DIAGRAM:
D1  A B
D3  AB
A
A B
B
D0 AB
D1  A B
D2  A B
D3 A B
3 to 8 Line Decoder:
 Block diagram of 3 to 8 decoder is shown in fig
 A, B and C are the inputs. ( No. of inputs =3)
 No. of possible input combinations: 23=8
 No. of Outputs : 23=8, they are indicated by D0 to D7
 From the Truth Table it is clear that each output is “1” for only specific
combination of inputs.
3 X 8
Decoder
A
B
C
. D0
.
.
.
D7
Outputs
Inputs
TRUTH TABLE FOR 3 X 8 DECODER:
INPUTS OUTPUTS
A B C D0 D1 D2 D3 D4 D5 D6 D7
0 0 0 1 0 0 0 0 0 0 0 D0 ABC
0 0 1 0 1 0 0 0 0 0 0 D1 ABC
0 1 0 0 0 1 0 0 0 0 0 D2 ABC
0 1 1 0 0 0 1 0 0 0 0 D3 ABC
1 0 0 0 0 0 0 1 0 0 0 D4 ABC
1 0 1 0 0 0 0 0 1 0 0 D5 ABC
1 1 0 0 0 0 0 0 0 1 0 D6 ABC
1 1 1 0 0 0 0 0 0 0 1 D7 ABC
LOGIC DIAGRAM OF 3 X 8 DECODER:
D0  A B C
D1  A B C
D2 A B C
D3 A B C
D4  A B C
D5  A B C
D6  A B C
D7  A B C
A B C
OUTPUTS
INPUTS
A B C
3 x 8 Decoder From 2 x 4 Decoder:
2 x 4 Decoder
2 x 4 Decoder
X
Y
E'
D0
D1
D2
D3
D4
D5
D6
D7
OUTPUT
INPUT
2
3
4
5
6
7
Example: Implement the following multiple output function using a suitable
Decoder.
f1(A, B, C) = ∑m(0,4,7)+ d(2,3)
f2 (A, B, C) =∑m (1,5,6)
f3 (A, B, C) =∑m (0,2,4,6)
Solution: f1 consists of don’t care conditions. So we consider them to be logic 1.
0
1
f1(A, B, C)
f2 (A, B, C)
f3 (A, B, C)
3
x
8
Decoder
A
B
C
INPUTS
EXAMPLE: Implement the following Boolean function using suitable Decoder.
f1 (x,y,z)=∑m(1,5,7)
f2 (x,y,z)=∑m(0,3)
f3 (x,y,z)=∑m(2,4,5)
Solution:
X
Y
Z
E
3
X
8
Decoder
0
1
2
3
4
5
6
7
INPUTS
f1 (x,y,z)
f2 (x,y,z)
f3 (x,y,z)
F1 (x, y ,z )  x y z  x z
F2 (x, y,z)  x y z  x z
SOLUTION: STEP 1: Write the given function F1 in SOP form
F1(x, y,z)  x y z  (y  y ) x z
F1(x, y,z)  x y z  x y z  x y z
F1(x, y,z)  m (0,5,7)
F2 (x, y,z)  x y z  x z
F2 (x, y,z)  x y z  (y  y ) x z
F2 (x, y,z)  x y z  x y z  x y z
F2 (x, y,z)  m (1,3,6)
Implementation using Decoder
0
1
2
3
4
5
6
7
F1
F2
3 x 8
Decoder
X
Y
Z
ENCODER
• An Encoder is a combinational logic circuit.
• It performs the inverse operation of Decoder.
• The opposite process of decoding is known as Encoding.
• An Encoder converts an active input signal into a coded output signal.
• Block diagram of Encoder is shown in Fig.10. It has ‘M’ inputs and ‘N’
outputs.
• An Encoder has ‘M’ input lines, only one of which is activated at a given
time, and produces an N-bit output code, depending on which input is
activated.
-
-
-
-
-
-
-
-
-
-
-
-
-
-
‘M’
Inputs
‘N’
Outputs
Encoder
A0
A1
A2
AM-1
B0
B1
B2
BN-1
• Encoders are used to translate the rotary or linear motion into a digital
signal.
• The difference between Decoder and Encoder is that Decoder has Binary
Code as an input while Encoder has Binary Code as an output.
• Encoder is an Electronics device that converts the analog signal to digital
signal such as BCD Code.
• Types of Encoders
i. Priority Encoder
ii. Decimal to BCD Encoder
iii. Octal to Binary Encoder
iv. Hexadecimal to Binary Encoder
Encoder
4 x 2
Decoder
2 x 4
A0
A1
A2
A3
M=4
M=22
M=2N
‘M’is the input and
‘N’is the output
B0
B1
B2
B3
Encoder
4 x 2
A0
A1
A2
A3
Decoder
2 x 4
M=4
M=22
M=2N
‘M’is the input and
‘N’is the output
00
01
10
11
Encoder
4 x 2
A0
A1
A2
A3
Decoder
2 x 4
M=4
M=22
M=2N
‘M’is the input and
‘N’is the output
00
01
10
11
1
0
Encoder
4 x 2
A0
A1
A2
A3
Decoder
2 x 4
M=4
M=22
M=2N
‘M’is the input and
‘N’is the output
00
01
10
11
1
0 10
PRIORITY ENCODER:
• As the name indicates, the priority is given to inputs line.
• If two or more input lines are high at the same time i.e 1 at the same time, then
the input line with high priority shall be considered.
D3
D2
D1
D0
Y1
Y0
Highest Priority
Input
Priority
Encoder
Lowest Priority Output
Input
Block Diagram of Priority
Encoder
INPUTS OUTPUTS V
D3 D2 D1 D0 Y1 Y0
0 0 0 0 x x 0
0 0 0 1 0 0 1
0 0 1 x 0 1 1
0 1 x x 1 0 1
1 x x x 1 1 1
TRUTH TABLE:
X 0 0 0
1 1 1 1
1 1 1 1
1 1 1 1
00
01
11
10 10
11
01
00 X 0 1 1
0 0 0 0
1 1 1 1
1 1 1 1
D3D2
D3D2
D1D0
D1D0
00 01 11 10 00 01 11 10
2 1
3
0
Y  D  D D
• There are four inputs D0, D1,D2, D3 and two outputsY1 and Y2.
• D3 has highest priority and D0 is at lowest priority.
• If D3=1 irrespective of other inputs then outputY1Y0=11.
• D3 is at highest priority so other inputs are considered as don’t care.
Y1  D2  D3
Y1  D2  D3
Y0  D3  D2 D1
D3 D2 D1 D0
Y1
Y0
DECIMAL TO BCD ENCODER:
• It has ten inputs corresponding to ten decimal digits (from 0 to 9) and four
outputs (A,B,C,D) representing the BCD.
-
-
-
-
-
-
-
-
-
ENCODER
C
0
1
2
9
INPUTS
A
B
D
OUTPUTS
INPUTS BCD OUTPUTS
0 1 2 3 4 5 6 7 8 9 A B C D
1 0 0 0 0 0 0 0 0 0 0 0 0 0
0 1 0 0 0 0 0 0 0 0 0 0 0 1
0 0 1 0 0 0 0 0 0 0 0 0 1 0
0 0 0 1 0 0 0 0 0 0 0 0 1 1
0 0 0 0 1 0 0 0 0 0 0 1 0 0
0 0 0 0 0 1 0 0 0 0 0 1 0 1
0 0 0 0 0 0 1 0 0 0 0 1 1 0
0 0 0 0 0 0 0 1 0 0 0 1 1 1
0 0 0 0 0 0 0 0 1 0 1 0 0 0
0 0 0 0 0 0 0 0 0 1 1 0 0 1
+5V
0
1
2
3
4
5
6
7
8
9
A B C D
OCTAL TO BINARY ENCODER:
D0
D1
D2
D3
D4
D5
D6
D7
X
Y
Z
INPUT OUTPUT
ENCODER
INPUT OUTPUT
D0 D1 D2 D3 D4 D5 D6 D7 X Y Z
1 0 0 0 0 0 0 0 0 0 0
0 1 0 0 0 0 0 0 0 0 1
0 0 1 0 0 0 0 0 0 1 0
0 0 0 1 0 0 0 0 0 1 1
0 0 0 0 1 0 0 0 1 0 0
0 0 0 0 0 1 0 0 1 0 1
0 0 0 0 0 0 1 0 1 1 0
0 0 0 0 0 0 0 1 1 1 1
X  D4  D5  D6  D7
Y  D2  D3  D6  D7
Z  D1  D3  D5  D7
D4 D5
LOGIC DIAGRAM:
D0 D1 D2 D3 D6 D7
X  D4  D5  D6  D7
Y  D2  D3  D6  D7
Z  D1  D3  D5  D7
Code Converter (Binary to BCD)
Code Converter (Binary to BCD)
Code Converter (Binary to BCD)
Code Converter (Binary to BCD)
Code Converter (Binary to BCD)
Code Converter (Binary to BCD)
Code Converter (BCD to Excess 3)
BCD input Excess – 3 output
B3 B2 B1 B0 E3 E2 E1 E0
0 0 0 0 0 0 1 1
0 0 0 1 0 1 0 0
0 0 1 0 0 1 0 1
0 0 1 1 0 1 1 0
0 1 0 0 0 1 1 1
0 1 0 1 1 0 0 0
0 1 1 0 1 0 0 1
0 1 1 1 1 0 1 0
1 0 0 0 1 0 1 1
1 0 0 1 1 1 0 0
1 0 1 0 x x x x
1 0 1 1 x x x x
1 1 0 0 x x x x
1 1 0 1 x x x x
1 1 1 0 x x x x
1 1 1 1 x x x x
Code Converter (BCD to Excess 3)
K-Map for E3 K-Map for E2
E3 = B3 + B2 (B0 + B1) E2 = B2 ⊕ (B0 + B1)
Code Converter (BCD to Excess 3)
K-Map for E1 K-Map for E0
Code Converter (BCD to Excess 3)
Code Converter (Excess 3 to BCD)
Excess-3 Input BCD Output
X4 X3 X2 X1 D C B A
0 0 0 0 X X X X
0 0 0 1 X X X X
0 0 1 0 X X X X
0 0 1 1 0 0 0 0
0 1 0 0 0 0 0 1
0 1 0 1 0 0 1 0
0 1 1 0 0 0 1 1
0 1 1 1 0 1 0 0
1 0 0 0 0 1 0 1
1 0 0 1 0 1 1 0
1 0 1 0 0 1 1 1
1 0 1 1 1 0 0 0
1 1 0 0 1 0 0 1
1 1 0 1 X X X X
1 1 1 0 X X X X
1 1 1 1 X X X X
Code Converter (Excess 3 to BCD)
A = X1 X2 + X3 X4 X1
Code Converter (Excess 3 to BCD)
Code Converter (Excess 3 to BCD)
Memory Elements
• The desired operation is that the alarm turns on when the sensor generates a
positive voltage signal, Set, in response to some event.
• Once the alarm is triggered, it must remain active even if the sensor output
goes back to zero.
• The alarm is turned off manually by means of a Reset input.
• The circuit requires a memory element to remember that the alarm has to be
active until the Reset signal arrives
Latch
A Latch is a special type of logical circuit. The latches have low and high two
stable states. Due to these states, latches also refer to as bistable-
multivibrators. A latch is a storage device that holds the data using the
feedback lane
SR Latch
INPUTS OUTPUTS
R S
Qn
(Present
State)
Qn+1
(Next State)
0 0 0 0
0 0 1 1
0 1 0 1
0 1 1 1
1 0 0 0
1 0 1 0
1 1 0 Indeterminate
1 1 1 Indeterminate
SR Latch
Gated SR Latch
To ensure a meaningful operation of the gated SR latch, it is essential to avoid
the possibility of having both the S and R inputs equal to 1 when Clk changes
from 1 to 0.
SR Flip Flop
Classification
• SR Latch
• Gated S-R Latch
• D latch
• Gated D Latch
• JK Latch
• T Latch.
Latch Flip Flop
• SR Flip-Flop
• D Flip-Flop
• JK Flip-Flop
• T Flip-Flop
D Latch
INPUTS OUTPUTS
R S
Qn+1
(Next State)
0 0 Qn
0 1 1
1 0 0
1 1 Indeterminate
Gated D Latch
JK Latch
INPUTS OUTPUTS
K J
Qn
(Present
State)
Qn+1
(Next State)
0 0 0 0
0 0 1 1
0 1 0 1
0 1 1 1
1 0 0 0
1 0 1 0
1 1 0 1
1 1 1 0
JK Latch
INPUTS OUTPUTS
K J
Qn+1
(Next State)
0 0 Qn
0 1 1
1 0 0
1 1 (Qn)’
INPUTS OUTPUTS
K J
Qn+1
(Next State)
0 0 No Change
0 1 Set
1 0 Reset
1 1 Toggle
T Latch
INPUTS OUTPUTS
T Qn
Qn+1
(Next State)
0 0 0
0 1 1
1 0 1
1 1 0
Clocked RS Flip-Flop
Qt+1 = S + 𝑹Qt
D Flip-Flop
INPUTS OUTPUTS
CLK D Qn
Qn+1
(Next
State)
1 0 0 0
1 0 1 0
1 1 0 1
1 1 1 1
Qt+1 = D
JK Flip flop (Jack Kilby)
R
S
INPUTS OUTPUTS
CLK K J
Qn+1
(Next
State)
1 0 0 No Change
1 0 1 Set
1 1 0 Reset
1 1 1 Toggle
Qt+1 = J𝐐𝐭 + 𝐊Qt
T Flip-Flop
Logic Symbol
INPUTS OUTPUTS
CLK T Qn
Qn+1
(Next
State)
1 0 0 0
1 0 1 1
1 1 0 1
1 1 1 0
Qt+1 = T𝑸𝒕 + 𝑻Qt
FlipFlops
Flip Flops Conversion
 In the previous Class, we discussed the four flip-flops, namely SR flip-
flop, D flip-flop, JK flip-flop & T flip-flop.
 We can convert one flip-flop into the remaining three flip-flops by
including some additional logic. So, there will be total of twelve flip-flop
conversions.
• JK flip-flop to T flip-flop
• JK flip-flop to D flip-flop
• JK flip-flop to SR flip-flop
• T flip-flop to D flip-flop
• T flip-flop to SR flip-flop
• T flip-flop to JK flip-flop
• D flip-flop to T flip-flop
• D flip-flop to SR flip-flop
• D flip-flop to JK flip-flop
• SR flip-flop to D flip-flop
• SR flip-flop to JK flip-flop
• SR flip-flop to T flip-flop
PROCEDURE FOR CONVERSION
SR to D
Step-1:
We construct the characteristic table of D flip-flop and excitation table of S-R flip-
flop.
SR to D
Step-2:
Using the K-map we find the boolean expression of S and R in terms of D
S = D R = D'
SR to D
Step-3:
We construct the circuit diagram of the conversion of S-R flip-flop into D flip-flop.
SHIFT REGISTER
The Shift Register is another type of sequential logic circuit that can be
used for the storage or the transfer of binary data
SISO
SIPO
PISO
PISO
PIPO
Sequential Circuit
Synchronous Counter
Asynchronous Counter
Finite State Machine (FSM)
Moore Vs Mealy Machine
Design Process
Analysis of Sequential Logic Circuit
Type of circuit Excitation
equations
Next state
equations
Mealy
sequential
machine.
Analysis of Sequential Logic Circuit
Next state equations
Excitation equations
Analysis of Sequential Logic Circuit
Next state equations State Table
Analysis of Sequential Logic Circuit
Next state equations State Table
Analysis of Sequential Logic Circuit
State Table
State Diagram
Analysis of Sequential Logic Circuit
Type of circuit Excitation
equations
Next state
equations
Moore
sequential
machine.
Analysis of Sequential Logic Circuit
Next state equations
State Table
Analysis of Sequential Logic Circuit
State Table State Diagram
Design of Sequential Logic Circuit
Design a sequential circuit using D flip-flop for a state diagram shown
Design of Sequential Logic Circuit
State Table
State Diagram
Design of Sequential Logic Circuit
Excitation Table
Excitation table of D-FF
Design of Sequential Logic Circuit
Excitation Table
K-map
Design of Sequential Logic Circuit
K-map
Circuit Diagram
Serial Adder
Serial Adder
Serial Adder
Serial Adder
Serial Adder

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Digital VLSI - Unit 2.pptx

  • 1. Unit -2 Digital Circuits Design Combinational Logic Design; Adders, Subtractor, Multiplier, Multiplexers, Demultiplexers, Decoders, Encoders, Code Converters. Sequential Logic Design- Flip-Flops, Registers, Counters, Finite State Machines-Mealy and Moore type, Serial Adder CO2 : Discuss about the different combinational and sequential logic blocks. (K3)
  • 2. Combinational Vs Sequential Circuits Combinational Circuit Sequential Circuit
  • 4. Binary Adder 1-bit Adder N-bit Adder 1 bit adder without carry (A+B) [Half Adder] 1 bit adder with carry (A+B+Cin) [Full Adder] 2 bit Adder [A1A0 + B1B0] 4 bit Adder [A3A2A1A0 + B3B2B1B0] Example: • Ripple Carry Adder • BCD Adder
  • 12. 4-bit Ripple Carry Addition: Example C0 FA A0 S0 B0 FA A1 S1 B1 FA A2 S2 B2 FA A3 S3 B3 C4 C1 C2 C3 T=1 0 0 1 0 1 0 0 1 0 0 1 0 0 1 1 1 0 0 0 0 0 0 0 0 0 T=0 B=0101 A=0011 S=0000 S=0110 0 0 1 0 0 1 0 1 T=2 S=0100 0 0 0 1 0 1 0 1 T=3 S=0000 1 0 0 1 0 1 0 1 T=4 S=1000
  • 14. Carry-Look Ahead Adder Propagate Propagate Generate Generate Inputs Outputs ci ai bi si ci+1 0 0 0 0 0 0 0 1 1 0 0 1 0 1 0 0 1 1 0 1 1 0 0 1 0 1 0 1 0 1 1 1 0 0 1 1 1 1 1 1
  • 15. Carry-Look Ahead Adder Gi = AiBi Pi = Ai ⊕Bi Gi is known as the carry Generate signal Pi is known as the carry propagate signal Si = Pi ⊕ Ci Ci+1 = Gi + PiCi
  • 16. Carry-Look Ahead Adder Si = Pi ⊕ Ci Ci+1= Gi + PiCi C1= G0 + P0C0 C2= G1 + P1C1 C3= G2 + P2C2 C4= G3 + P3C3 S0= P0 ⊕ C0 S1= P1 ⊕ C1 S2= P2 ⊕ C2 S3= P3 ⊕ C3 Gi= Ai . Bi G0 = A0 .B0 G1 = A1 .B1 G2 = A2 .B2 G3 = A3 .B3 Pi= Ai ⊕ Bi P0 = A0 ⊕ B0 P1 = A1 ⊕ B1 P2 = A2 ⊕ B2 P3 = A3 ⊕ B3
  • 17. c1 = G0 + P0c0 c2 = G1 + P1c1 c2 = G1 + P1(G0 + P0c0) c2 = G1 + P1G0 + P1P0c0 c3 = G2 + P2c2 c3 = G2 + P2(G1 + P1G0 + P1P0c0) c3 = G2 + P2G1 + P2P1G0 + P2P1P0c0 c4 = G3 + P3G2 + P3P2G1 + P3P2P1G0 + P3P2P1P0c0 Gi = ai . bi (generate) Pi = ai ⊕ bi (propagate) Gi/Pi function of inputs only Carry-Look Ahead Adder C1 = G0 + P0C0 C2 = G1 + P1C1 = G1 + P1 (G0 + P0C0) = G1 + P1G0 + P1P0C0 C3 = G2 + P2C2 = G2 + P2G1 + P2P1G0 + P2P1P0C0 C4 = G3 + P3C3 = G3 + P3G2 + P3P2G1 + P3P2P1G0 + P3P2P1P0C0
  • 20. BCD Adder Sum Sum > 9 S3 S2 S1 S0 Y 0 0 0 0 0 0 0 0 1 0 0 0 1 0 0 0 0 1 1 0 0 1 0 0 0 0 1 0 1 0 0 1 1 0 0 0 1 1 1 0 1 0 0 0 0 1 0 0 1 0 1 0 1 0 1 1 0 1 1 1 1 1 0 0 1 1 1 0 1 1 1 1 1 0 1 1 1 1 1 1 Number > 9
  • 22. BCD Adder 0000 (Sum <9) 0110 (Sum >9)
  • 25. Binary multiplier Two-bit by two-bit binary multiplier
  • 26. Binary multiplier Four-bit by three-bit binary multiplier
  • 30. Magnitude Comparator [2 bit] A>B: A1B1’ + A0B1’B0’ + A1A0B0’ A=B: A1’A0’B1’B0’ + A1’A0B1’B0 + A1A0B1B0 + A1A0’B1B0’
  • 31. Magnitude Comparator [2 bit] A<B:A1’B1 + A0’B1B0 + A1’A0’B0
  • 34. Multiplexer • A MUX is a digital switch that has multiple inputs (sources) and a single output (destination). • The select lines determine which input is connected to the output. • MUX Types  2-to-1 (1 select line)  4-to-1 (2 select lines)  8-to-1 (3 select lines)  16-to-1 (4 select lines) Select Lines Inputs (sources) Output (destination) 1 2N N MUX
  • 36. Multiplexer [4:1] S1 S0 Y 0 0 I0 0 1 I1 1 0 I2 1 1 I3
  • 37. Implement AND gate using 2:1 MUX
  • 38. Implement OR gate using 2:1 MUX
  • 39. Implement 4:1 MUX using 2:1 MUX S1 S0 Y 0 0 I0 0 1 I1 1 0 I2 1 1 I3
  • 40. Implement f(a, b, c) = a’b’c + ab using 8:1 MUX Canonical Form :
  • 41. Implement f(a, b, c) = a’b’c + ab using 4:1 MUX
  • 42. f ( A, B, C) = Σ ( 1, 2, 3, 5, 6 ) with don’t care (7) using 4 : 1 MUX with AB as select lines
  • 43. f ( A, B, C) = Σ ( 1, 2, 3, 5, 6 ) with don’t care (7) using 4 : 1 MUX with AC as select lines
  • 47. Encoder An encoder is a circuit that accepts many inputs and generates the output in a coded form. Encoder is a device which has 2n' inputs and 'n' numberof output
  • 48. • Adecoder is a combinational circuit. • A decoder accepts a set of inputs that represents a binary number and activates only that output corresponding to the input number.All other outputs remain inactive. • There are 2N possible input combinations, for each of these input combination only one output will be HIGH (active) all other outputs are LOW • Some decoder have one or more ENABLE (E) inputs that are used to control the operation of decoder. Decoder
  • 49. BLOCK DIAGRAM OF DECODER DECODER A0 A1 A2 AN-1 . . . . N- Inputs M- Outputs Only one output is High for each input . . . . B0 B1 B2 BM-1
  • 50. 2 to 4 Line Decoder:  Block diagram of 2 to 4 decoder is shown in fig.  Aand B are the inputs. ( No. of inputs =2)  No. of possible input combinations: 22=4  No. of Outputs : 22=4, they are indicated by D0, D1, D2 and D3  From the Truth Table it is clear that each output is “1” for only specific combination of inputs. A B 0 D D1 D2 3 2 X 4 Decoder INPUTS OUTPUTS A B D0 D1 D2 D3 0 0 1 0 0 0 0 1 0 1 0 0 1 0 0 0 1 0 1 1 0 0 0 1 TRUTH TABLE Inputs D Outputs
  • 51. BOOLEAN EXPRESSION: From Truth Table D0 A B D2 A B LOGIC DIAGRAM: D1  A B D3  AB A A B B D0 AB D1  A B D2  A B D3 A B
  • 52. 3 to 8 Line Decoder:  Block diagram of 3 to 8 decoder is shown in fig  A, B and C are the inputs. ( No. of inputs =3)  No. of possible input combinations: 23=8  No. of Outputs : 23=8, they are indicated by D0 to D7  From the Truth Table it is clear that each output is “1” for only specific combination of inputs. 3 X 8 Decoder A B C . D0 . . . D7 Outputs Inputs
  • 53. TRUTH TABLE FOR 3 X 8 DECODER: INPUTS OUTPUTS A B C D0 D1 D2 D3 D4 D5 D6 D7 0 0 0 1 0 0 0 0 0 0 0 D0 ABC 0 0 1 0 1 0 0 0 0 0 0 D1 ABC 0 1 0 0 0 1 0 0 0 0 0 D2 ABC 0 1 1 0 0 0 1 0 0 0 0 D3 ABC 1 0 0 0 0 0 0 1 0 0 0 D4 ABC 1 0 1 0 0 0 0 0 1 0 0 D5 ABC 1 1 0 0 0 0 0 0 0 1 0 D6 ABC 1 1 1 0 0 0 0 0 0 0 1 D7 ABC
  • 54. LOGIC DIAGRAM OF 3 X 8 DECODER: D0  A B C D1  A B C D2 A B C D3 A B C D4  A B C D5  A B C D6  A B C D7  A B C A B C OUTPUTS INPUTS A B C
  • 55. 3 x 8 Decoder From 2 x 4 Decoder: 2 x 4 Decoder 2 x 4 Decoder X Y E' D0 D1 D2 D3 D4 D5 D6 D7 OUTPUT INPUT
  • 56. 2 3 4 5 6 7 Example: Implement the following multiple output function using a suitable Decoder. f1(A, B, C) = ∑m(0,4,7)+ d(2,3) f2 (A, B, C) =∑m (1,5,6) f3 (A, B, C) =∑m (0,2,4,6) Solution: f1 consists of don’t care conditions. So we consider them to be logic 1. 0 1 f1(A, B, C) f2 (A, B, C) f3 (A, B, C) 3 x 8 Decoder A B C INPUTS
  • 57. EXAMPLE: Implement the following Boolean function using suitable Decoder. f1 (x,y,z)=∑m(1,5,7) f2 (x,y,z)=∑m(0,3) f3 (x,y,z)=∑m(2,4,5) Solution: X Y Z E 3 X 8 Decoder 0 1 2 3 4 5 6 7 INPUTS f1 (x,y,z) f2 (x,y,z) f3 (x,y,z)
  • 58. F1 (x, y ,z )  x y z  x z F2 (x, y,z)  x y z  x z SOLUTION: STEP 1: Write the given function F1 in SOP form F1(x, y,z)  x y z  (y  y ) x z F1(x, y,z)  x y z  x y z  x y z F1(x, y,z)  m (0,5,7) F2 (x, y,z)  x y z  x z F2 (x, y,z)  x y z  (y  y ) x z F2 (x, y,z)  x y z  x y z  x y z F2 (x, y,z)  m (1,3,6) Implementation using Decoder
  • 60. ENCODER • An Encoder is a combinational logic circuit. • It performs the inverse operation of Decoder. • The opposite process of decoding is known as Encoding. • An Encoder converts an active input signal into a coded output signal. • Block diagram of Encoder is shown in Fig.10. It has ‘M’ inputs and ‘N’ outputs. • An Encoder has ‘M’ input lines, only one of which is activated at a given time, and produces an N-bit output code, depending on which input is activated. - - - - - - - - - - - - - - ‘M’ Inputs ‘N’ Outputs Encoder A0 A1 A2 AM-1 B0 B1 B2 BN-1
  • 61. • Encoders are used to translate the rotary or linear motion into a digital signal. • The difference between Decoder and Encoder is that Decoder has Binary Code as an input while Encoder has Binary Code as an output. • Encoder is an Electronics device that converts the analog signal to digital signal such as BCD Code. • Types of Encoders i. Priority Encoder ii. Decimal to BCD Encoder iii. Octal to Binary Encoder iv. Hexadecimal to Binary Encoder
  • 62. Encoder 4 x 2 Decoder 2 x 4 A0 A1 A2 A3 M=4 M=22 M=2N ‘M’is the input and ‘N’is the output B0 B1 B2 B3
  • 63. Encoder 4 x 2 A0 A1 A2 A3 Decoder 2 x 4 M=4 M=22 M=2N ‘M’is the input and ‘N’is the output 00 01 10 11
  • 64. Encoder 4 x 2 A0 A1 A2 A3 Decoder 2 x 4 M=4 M=22 M=2N ‘M’is the input and ‘N’is the output 00 01 10 11 1 0
  • 65. Encoder 4 x 2 A0 A1 A2 A3 Decoder 2 x 4 M=4 M=22 M=2N ‘M’is the input and ‘N’is the output 00 01 10 11 1 0 10
  • 66. PRIORITY ENCODER: • As the name indicates, the priority is given to inputs line. • If two or more input lines are high at the same time i.e 1 at the same time, then the input line with high priority shall be considered. D3 D2 D1 D0 Y1 Y0 Highest Priority Input Priority Encoder Lowest Priority Output Input Block Diagram of Priority Encoder INPUTS OUTPUTS V D3 D2 D1 D0 Y1 Y0 0 0 0 0 x x 0 0 0 0 1 0 0 1 0 0 1 x 0 1 1 0 1 x x 1 0 1 1 x x x 1 1 1 TRUTH TABLE:
  • 67. X 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 00 01 11 10 10 11 01 00 X 0 1 1 0 0 0 0 1 1 1 1 1 1 1 1 D3D2 D3D2 D1D0 D1D0 00 01 11 10 00 01 11 10 2 1 3 0 Y  D  D D • There are four inputs D0, D1,D2, D3 and two outputsY1 and Y2. • D3 has highest priority and D0 is at lowest priority. • If D3=1 irrespective of other inputs then outputY1Y0=11. • D3 is at highest priority so other inputs are considered as don’t care. Y1  D2  D3
  • 68. Y1  D2  D3 Y0  D3  D2 D1 D3 D2 D1 D0 Y1 Y0
  • 69. DECIMAL TO BCD ENCODER: • It has ten inputs corresponding to ten decimal digits (from 0 to 9) and four outputs (A,B,C,D) representing the BCD. - - - - - - - - - ENCODER C 0 1 2 9 INPUTS A B D OUTPUTS
  • 70. INPUTS BCD OUTPUTS 0 1 2 3 4 5 6 7 8 9 A B C D 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 1 0 0 1 0 0 0 0 0 0 0 0 0 1 0 0 0 0 1 0 0 0 0 0 0 0 0 1 1 0 0 0 0 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 1 0 0 0 0 0 1 0 1 0 0 0 0 0 0 1 0 0 0 0 1 1 0 0 0 0 0 0 0 0 1 0 0 0 1 1 1 0 0 0 0 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0 0 1
  • 72. OCTAL TO BINARY ENCODER: D0 D1 D2 D3 D4 D5 D6 D7 X Y Z INPUT OUTPUT ENCODER
  • 73. INPUT OUTPUT D0 D1 D2 D3 D4 D5 D6 D7 X Y Z 1 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 1 0 0 1 0 0 0 0 0 0 1 0 0 0 0 1 0 0 0 0 0 1 1 0 0 0 0 1 0 0 0 1 0 0 0 0 0 0 0 1 0 0 1 0 1 0 0 0 0 0 0 1 0 1 1 0 0 0 0 0 0 0 0 1 1 1 1
  • 74. X  D4  D5  D6  D7 Y  D2  D3  D6  D7 Z  D1  D3  D5  D7 D4 D5 LOGIC DIAGRAM: D0 D1 D2 D3 D6 D7 X  D4  D5  D6  D7 Y  D2  D3  D6  D7 Z  D1  D3  D5  D7
  • 81. Code Converter (BCD to Excess 3) BCD input Excess – 3 output B3 B2 B1 B0 E3 E2 E1 E0 0 0 0 0 0 0 1 1 0 0 0 1 0 1 0 0 0 0 1 0 0 1 0 1 0 0 1 1 0 1 1 0 0 1 0 0 0 1 1 1 0 1 0 1 1 0 0 0 0 1 1 0 1 0 0 1 0 1 1 1 1 0 1 0 1 0 0 0 1 0 1 1 1 0 0 1 1 1 0 0 1 0 1 0 x x x x 1 0 1 1 x x x x 1 1 0 0 x x x x 1 1 0 1 x x x x 1 1 1 0 x x x x 1 1 1 1 x x x x
  • 82. Code Converter (BCD to Excess 3) K-Map for E3 K-Map for E2 E3 = B3 + B2 (B0 + B1) E2 = B2 ⊕ (B0 + B1)
  • 83. Code Converter (BCD to Excess 3) K-Map for E1 K-Map for E0
  • 84. Code Converter (BCD to Excess 3)
  • 85. Code Converter (Excess 3 to BCD) Excess-3 Input BCD Output X4 X3 X2 X1 D C B A 0 0 0 0 X X X X 0 0 0 1 X X X X 0 0 1 0 X X X X 0 0 1 1 0 0 0 0 0 1 0 0 0 0 0 1 0 1 0 1 0 0 1 0 0 1 1 0 0 0 1 1 0 1 1 1 0 1 0 0 1 0 0 0 0 1 0 1 1 0 0 1 0 1 1 0 1 0 1 0 0 1 1 1 1 0 1 1 1 0 0 0 1 1 0 0 1 0 0 1 1 1 0 1 X X X X 1 1 1 0 X X X X 1 1 1 1 X X X X
  • 86. Code Converter (Excess 3 to BCD) A = X1 X2 + X3 X4 X1
  • 89. Memory Elements • The desired operation is that the alarm turns on when the sensor generates a positive voltage signal, Set, in response to some event. • Once the alarm is triggered, it must remain active even if the sensor output goes back to zero. • The alarm is turned off manually by means of a Reset input. • The circuit requires a memory element to remember that the alarm has to be active until the Reset signal arrives
  • 90. Latch A Latch is a special type of logical circuit. The latches have low and high two stable states. Due to these states, latches also refer to as bistable- multivibrators. A latch is a storage device that holds the data using the feedback lane
  • 91. SR Latch INPUTS OUTPUTS R S Qn (Present State) Qn+1 (Next State) 0 0 0 0 0 0 1 1 0 1 0 1 0 1 1 1 1 0 0 0 1 0 1 0 1 1 0 Indeterminate 1 1 1 Indeterminate
  • 93. Gated SR Latch To ensure a meaningful operation of the gated SR latch, it is essential to avoid the possibility of having both the S and R inputs equal to 1 when Clk changes from 1 to 0.
  • 95. Classification • SR Latch • Gated S-R Latch • D latch • Gated D Latch • JK Latch • T Latch. Latch Flip Flop • SR Flip-Flop • D Flip-Flop • JK Flip-Flop • T Flip-Flop
  • 96. D Latch INPUTS OUTPUTS R S Qn+1 (Next State) 0 0 Qn 0 1 1 1 0 0 1 1 Indeterminate
  • 98. JK Latch INPUTS OUTPUTS K J Qn (Present State) Qn+1 (Next State) 0 0 0 0 0 0 1 1 0 1 0 1 0 1 1 1 1 0 0 0 1 0 1 0 1 1 0 1 1 1 1 0
  • 99. JK Latch INPUTS OUTPUTS K J Qn+1 (Next State) 0 0 Qn 0 1 1 1 0 0 1 1 (Qn)’ INPUTS OUTPUTS K J Qn+1 (Next State) 0 0 No Change 0 1 Set 1 0 Reset 1 1 Toggle
  • 100. T Latch INPUTS OUTPUTS T Qn Qn+1 (Next State) 0 0 0 0 1 1 1 0 1 1 1 0
  • 101. Clocked RS Flip-Flop Qt+1 = S + 𝑹Qt
  • 102. D Flip-Flop INPUTS OUTPUTS CLK D Qn Qn+1 (Next State) 1 0 0 0 1 0 1 0 1 1 0 1 1 1 1 1 Qt+1 = D
  • 103. JK Flip flop (Jack Kilby) R S INPUTS OUTPUTS CLK K J Qn+1 (Next State) 1 0 0 No Change 1 0 1 Set 1 1 0 Reset 1 1 1 Toggle Qt+1 = J𝐐𝐭 + 𝐊Qt
  • 104. T Flip-Flop Logic Symbol INPUTS OUTPUTS CLK T Qn Qn+1 (Next State) 1 0 0 0 1 0 1 1 1 1 0 1 1 1 1 0 Qt+1 = T𝑸𝒕 + 𝑻Qt
  • 106. Flip Flops Conversion  In the previous Class, we discussed the four flip-flops, namely SR flip- flop, D flip-flop, JK flip-flop & T flip-flop.  We can convert one flip-flop into the remaining three flip-flops by including some additional logic. So, there will be total of twelve flip-flop conversions. • JK flip-flop to T flip-flop • JK flip-flop to D flip-flop • JK flip-flop to SR flip-flop • T flip-flop to D flip-flop • T flip-flop to SR flip-flop • T flip-flop to JK flip-flop • D flip-flop to T flip-flop • D flip-flop to SR flip-flop • D flip-flop to JK flip-flop • SR flip-flop to D flip-flop • SR flip-flop to JK flip-flop • SR flip-flop to T flip-flop
  • 108. SR to D Step-1: We construct the characteristic table of D flip-flop and excitation table of S-R flip- flop.
  • 109. SR to D Step-2: Using the K-map we find the boolean expression of S and R in terms of D S = D R = D'
  • 110. SR to D Step-3: We construct the circuit diagram of the conversion of S-R flip-flop into D flip-flop.
  • 111. SHIFT REGISTER The Shift Register is another type of sequential logic circuit that can be used for the storage or the transfer of binary data
  • 112. SISO
  • 113. SIPO
  • 114. PISO
  • 115. PISO
  • 116. PIPO
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  • 177. Moore Vs Mealy Machine
  • 179. Analysis of Sequential Logic Circuit Type of circuit Excitation equations Next state equations Mealy sequential machine.
  • 180. Analysis of Sequential Logic Circuit Next state equations Excitation equations
  • 181. Analysis of Sequential Logic Circuit Next state equations State Table
  • 182. Analysis of Sequential Logic Circuit Next state equations State Table
  • 183. Analysis of Sequential Logic Circuit State Table State Diagram
  • 184. Analysis of Sequential Logic Circuit Type of circuit Excitation equations Next state equations Moore sequential machine.
  • 185. Analysis of Sequential Logic Circuit Next state equations State Table
  • 186. Analysis of Sequential Logic Circuit State Table State Diagram
  • 187. Design of Sequential Logic Circuit Design a sequential circuit using D flip-flop for a state diagram shown
  • 188. Design of Sequential Logic Circuit State Table State Diagram
  • 189. Design of Sequential Logic Circuit Excitation Table Excitation table of D-FF
  • 190. Design of Sequential Logic Circuit Excitation Table K-map
  • 191. Design of Sequential Logic Circuit K-map Circuit Diagram

Editor's Notes

  1. VLSI Design II – © Kia Bazargan
  2. VLSI Design II – © Kia Bazargan
  3. VLSI Design II – © Kia Bazargan
  4. VLSI Design II – © Kia Bazargan