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REALISATION OF TWO -BIT FLASH ADC

Op-Amp & Linear IC’s Laboratory

(18EEL-48)

​

2 of 20

What is a flash-ADC?

  •  

Analog Input

Digital Output

Voltage Range

​

​

0-1.25V

0

0

1.25-2.5V

0

1

2.5-3.75V

1

0

3.75-5V

1

1

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CIRCUIT DIAGRAM OF TWO-BIT FLASH ADC

1

7

8

2

6

9

3

5

10

4

11

R

R

R

R

+5V

0-5V

 

GND

C

O

M

P

A

R

T

O

R

A

 

 

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1

7

8

2

6

9

3

5

10

4

11

R

R

R

R

+5V

0-5V

 

GND

C

O

M

P

A

R

T

O

R

A

 

 

COMPONENTS REQUIRED

5kΩ

Trainer Kit

5kΩ

5kΩ

5kΩ

Regulated Power Supply

LM324 IC

7404 IC

7408 IC

7432 IC

Patch Chords

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LM324IC

-

+

+

+

+

-

-

-

1

7

5

6

4

3

2

8

9

10

11

12

13

14

1

2

3

4

 

 

  • The IC has 4 independent operational amplifiers on a single chip.
  • These operational amplifier can be made to work like independent comparators.
  • The op-amp when used as a comparator is used to compare the voltages at inverting and non-inverting terminal.
  • When the input at non-inverting terminal is greater than input at inverting terminal the output will be at positive saturation voltage and vice-versa.

​

​

6 of 20

OPERATION OF TWO-BIT FLASH ADC

R

R

R

R

+5V

5kΩ

5kΩ

5kΩ

5kΩ

I

 

 

 

 

 

 

 

 

 

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R

R

R

R

+5V

5kΩ

5kΩ

5kΩ

5kΩ

I

 

 

 

1

2

3

+

-

-

-

+

+

Less than 1.25V

0

0

0

OPERATION OF TWO-BIT FLASH ADC

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R

R

R

R

+5V

5kΩ

5kΩ

5kΩ

5kΩ

I

 

 

 

1

2

3

+

-

-

-

+

+

1.25V

1

0

0

1.25V

1.25V

1.25V

OPERATION OF TWO-BIT FLASH ADC

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R

R

R

R

+5V

5kΩ

5kΩ

5kΩ

5kΩ

I

 

 

 

1

2

3

+

-

-

-

+

+

1.25V<V<2.5V

1

0

0

OPERATION OF TWO-BIT FLASH ADC

10 of 20

R

R

R

R

+5V

5kΩ

5kΩ

5kΩ

5kΩ

I

 

 

 

1

2

3

+

-

-

-

+

+

2.5V

1

0

2.5V

2.5V

1

2.5V

OPERATION OF TWO-BIT FLASH ADC

0

11 of 20

R

R

R

R

+5V

5kΩ

5kΩ

5kΩ

5kΩ

I

 

 

 

1

2

3

+

-

-

-

+

+

2.5V>V<3.75

1

0

1

0

OPERATION OF TWO-BIT FLASH ADC

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R

R

R

R

+5V

5kΩ

5kΩ

5kΩ

5kΩ

I

 

 

 

1

2

3

+

-

-

-

+

+

V=3.75V

1

0

1

 

 

 

0

1

OPERATION OF TWO-BIT FLASH ADC

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R

R

R

R

+5V

5kΩ

5kΩ

5kΩ

5kΩ

I

 

 

 

1

2

3

+

-

-

-

+

+

V>3.75V

1

0

1

0

1

OPERATION OF TWO-BIT FLASH ADC

14 of 20

R

R

R

R

+5V

5kΩ

5kΩ

5kΩ

5kΩ

I

 

 

 

1

2

3

+

-

-

-

+

+

0-5V

0

B

0

A

C

E

N

C

O

D

E

R

 

 

OPERATION OF TWO-BIT FLASH ADC

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1

7

8

2

6

9

3

5

10

4

11

R

R

R

R

+5V

0-5V

 

GND

C

O

M

P

A

R

T

O

R

A

A

B

C

E

N

C

O

D

E

R

 

 

OPERATION OF TWO-BIT FLASH ADC

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A

B

C

​

​

0

0

0

0

0

0

0

1

0

1

0

1

0

X

X

0

1

1

1

0

1

0

0

X

X

1

0

1

X

X

1

1

0

X

X

1

1

1

1

1

TRUTH TABLE

DESIGNING OF ENCODER

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A

B

C

​

0

0

0

0

0

0

1

1

0

1

0

X

0

1

1

0

1

0

0

X

1

0

1

X

1

1

0

X

1

1

1

1

TRUTH TABLE

​

​

​

​

​

​

​

​

A

BC

0

1

0 0

0 1

1 1

1 0

0

1

0

X

X

X

1

X

 

A

B C

 

DESIGNING OF ENCODER

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A

B

C

​

0

0

0

0

0

0

1

0

0

1

0

X

0

1

1

1

1

0

0

X

1

0

1

X

1

1

0

X

1

1

1

1

TRUTH TABLE

​

​

​

​

​

​

​

​

A

BC

0

1

0 0

0 1

1 1

1 0

0

0

1

X

X

X

1

X

 

B

 

DESIGNING OF ENCODER

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CIRCUIT DIAGRAM OF TWO-BIT FLASH ADC

1

7

8

2

6

9

3

5

10

4

11

R

R

R

R

+5V

0-5V

 

GND

L

M

3

4

2

A

B

C

B

C

B

 

B

C

 

1

2

2’

1’

3’

1’’

2’’

3’’

7404 IC

7408 IC

7432 IC

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EXPECTED OUTPUT

Analog Input

Digital Output

Voltage Range

​

​

0-1.25V

0

0

1.25-2.5V

0

1

2.5-3.75V

1

0

3.75-5V

1

1