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BRANCH-E&TC ENGINEERING

SEM – 3Rd

SUBJECT-DIGITAL ELECTRONICS

CHAPTER-01- BASIC OF DIGITAL ELECTRONICS

TOPIC- basic logic gates

Ay-2021-2022 ,winter-2021

FACULTY-ER S MOHANTA.(Hod e & tc engg Dept)

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Presentation On:-

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A/D & D/A Converter

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HYBRID SYSTEM�(BOTH ANALOG AND DIGITAL)

Digital

Processing

Unit

Decoder

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D/A

Converter

Encoder

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A/D

Converter

Analog

output

Analog

input

Converts from analog input

to digital output

Converts from digital input

to analog output

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A/D AND D/A CONVERTERS

Resistor

Network

Summing

Amplifier

0 1 1 0

Analog

Voltage

Digital-to-analog converter

INPUT

0 1 1 0

A/D

Analog-to-digital converter

Digital

Processing

Unit

Decoder

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D/A

Converter

Encoder

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A/D

Converter

Analog

output

Analog

input

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SIMPLE D/A CONVERTER

10 kΩ

3 V

Input resistors

Feedback resistor

Binary inputs

N = 4

Summing amplifier

(inverting)

37.5 kΩ

150 kΩ

75 kΩ

18.7 kΩ

2N = 16

This circuit can produce 16 different analog output voltages.

Vreference

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D/A CONVERTER OPERATION

10 kΩ

3 V

37.5 kΩ

150 kΩ

75 kΩ

18.7 kΩ

Binary input = 0000

= 0 V

Vout =

x 3 V = 0.2 V

10 kΩ

150 kΩ

The smallest step size for this circuit is 0.2 V.

0001

= 0.2 V

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4-BIT D/A CONVERTER

10 kΩ

3 V

The total span for this circuit is from 0 to 3 V.

As the binary input

steps from 0000 to 1111

Vout steps from

0 V to 3 V

0 V

3 V

Vout(max) = (2N - 1) x 0.2 V = 3 V

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COUNTER-RAMP TYPE A/D CONVERTER

When the ramp exceeds Vin

the comparator output goes

LOW and the clock is disabled.

Vin

ramp

Binary

output

Vin

Clock

ramp

Comparator

Counter

D/A

Converter

HIGH

LOW

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RAMP-TYPE A/D CONVERTER

Vin

Clock

Counter

Comparator

Ramp

Generator

Binary

output

0 1 0 1

Clock pulses to counter

Comparator output

Vin = + 5 V

LOW

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SUCCESSIVE-APPROXIMATION TYPE�A/D CONVERTER

Successive

Approximation

Logic

Voltage

Comparator

D/A

Converter

Vin

Clock

Binary output

7V input

0 1 1 1

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FLOWCHARTING SUCCESSIVE APPROXIMATION

Set 1s place

to 1

STOP

Final result= 0111

Is 0110

high or low?

HIGH

LOW

Set 2s place

to 1

Is 0100

high or low?

HIGH

LOW

7 V input

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Assume an input of

7V to a 4-bit binary output

A/D converter using

successive approximation

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Clear 8s.

Set 4s to 1.

Is 1000

high or low?

LOW

HIGH

Set MSB

to 1

Start

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A/D CONVERTER SPECIFICATIONS

  • Type of output
    • Binary (microprocessor-type)
    • Decimal (digital meter type)
  • Resolution
    • Binary output- number of bits (such as 4, 6, 8, 12, 14 or 16)
    • Decimal output- number of digits on display� (such as 3 1/2 or 4 1/2)
  • Accuracy
    • Binary output- (ranges from +/- 1/2 LSB to about +/- 2 LSB)
    • Decimal output- (ranges from about 0.01 to 0.05 percent)
  • Conversion time is the time it takes for the IC to convert the� analog input voltage to digital output. Binary output A/D� converters commonly have faster conversion times than� decimal output types.

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