Analog to Digital Converter

SUBMITTED BY:-Madhusudhan Agarwal

CONTENTS

Definition

Need of ADC in EMBEDDED

Registers of ADC

Types of ADC

Applications

DEFINITIONAn analog-to-digital converter, or ADC as it is more commonly

called, is a device that converts analog signals into digitalsignals.

OR

An analog-to-digital converter (ADC, A/D, or A to D) is a device that converts a continuous physical quantity (usually voltage) to a digital number that represents the quantity's amplitude

ANALOG-TO-DIGITAL CONVERSION

Terminology

analog: continuously valued signal, such as temperature or

speed, with infinite possible values in between

digital: discretely valued signal, such as integers, encoded in

binary

An embedded system’s surroundings typically involve many

analog signals.

ANALOG-TO-DIGITAL CONVERTERS

proportionality

Vmax = 7.5V

0V

11111110

0000

0010

0100

0110

1000

1010

1100

0001

0011

0101

0111

1001

1011

1101

0.5V1.0V1.5V2.0V2.5V3.0V

3.5V4.0V4.5V5.0V

5.5V6.0V6.5V7.0V

analog to digital

4

3

2

1

t1 t2 t3 t40100 0110 0110 0101

time

anal

og

inp

ut

(V)

Digital output

NEED OF ADC IN EMBEDDED

The microcontroller is a digital device so it needs digital input to process.But a number of input devices available which gives

analog signal.So its necessary to convert analog signals to digital

signalsIts done by Analog to Digital Circuit inside a

microcontroller.

REGISTERS OF ADC

There are four type of register which we use in ADC

A. ADMUX(ADC Multiplexer Selection Register)B. ADCSRA(ADC Status and Control Register)C. ADCH Storing the ADC resultD. ADCL

ADMUX(ADC MULTIPLEXER SELECTION REGISTER)

Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0

REFS1 REFS0 ADLAR MUX 4 MUX 3 MUX 2 MUX 1 MUX 0

0 0 0 0 0 0 0 0 Initial value

REFS1 REFS0 Vref

0 0 OFF

0 1 5V

1 0 REVERSE

1 1 2.56V

0 1 0 0 0 0 0 0

ADCSRA(ADC STATUS AND CONTROL REGISTER)

Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0

ADEN ADSC ADATE ADIF ADIE ADPS2 ADPS1 ADPS0

0 0 0 0 0 0 0 0 Initial value

ADC enable

ADC start conversion

Auto trigger enable

Interrupt flag

Interrupt enable

ADC pre scale factor

1 1 0 0 0 1 1 1

Types of Analog to Digital Converters

1. Counter Type

2. Integrating or Dual Slope

3. Parallel or Flash

4. Successive Approximation

Counter Type

Control Logic

D A C Counter

START

Vin

Comparator

Digital Output

clock

•When START is received,

•control logic initializes the system, (sets counter to 0), and

•turns on Clock sending regular pulses to the counter.

As the Clock sends regular pulses to the counter, the counter outputs a digital signal to the Digital-to-Analog converter

D A C Counter

START

Vin

Comparator

Digital Output

clock

Control Logic

Control Logic

D A CCounter

START

Vin

Comparator

Digital Output

clock

As the counter counts, its output to the D A C generates a staircase ramp to the comparator.

Control Logic

D A CCounter

START

Vin

Comparator

Digital Output

clock

As the ramp voltage increases to the comparator, it rises closer and closer to Vin at which point the comparator shifts states

Control Logic

D A C Counter

START

Vin

Comparator

Digital Output

clock

Once the digital output has been read by the associated circuitry, a new start signal is sent, repeating the cycle.

Track & Hold Logic

D A C

Up/Down Counter

Vin

Comparator

Digital Output

clock

Tracking ADC - similar to the counter type except it uses an up/down counter and can track a varying signal more quickly

Vin

-Vref

Control logic

Counter

clock

comparator

integrator

Digital Output

Integrating or Dual Slope A/D

Successive-Approximation A/D

Successive Approximation

Register

D/A ConverterVref

clock

analog input

Digital Output Data

At initialization, all bits from the SAR are set to zero, and conversion begins by taking STRT line low.

comparator

STRT

APPLICATIONS

Music recordingDigital signal processingScientific instruments

AND

Thank you……….