pras DE .pptx

7/29/2019 pras DE .pptx

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ANALOG TO DIGITAL

CONVERTER


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BASICS

ANALOG SIGNAL:

Continuously valued signal, such as temperature orspeed, with infinite possible values in between.

DIGITAL SIGNAL:

Discretely valued signal, such as integers,encoded in binary.


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A/D CONVERSION

Many embedded systems need to deal withnonelectric quantities.

These nonelectric quantities are analog in nature.

Analog quantities must be converted into digitalformat so that they can be processed by thecomputer.


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A/D CONVERSION


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A transducer can convert a nonelectric quantity intoan electric quantity.

The output of a transducer may not be in a suitable

range for A/D conversion. A signal conditioning circuit is needed for changing

the transducer output to a range suitable for A/Dconversion.

A/D CONVERSION


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A/D CONVERSION


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An analog-to-digital converter (abbreviated ADC,A/D or A to D) is a device that converts acontinuous analog quantity to a discrete timedigital representation.

Typically, an ADC is an electronic device thatconverts an input analog voltage or current to adigital number proportional to the magnitude ofthe voltage or current.

A/D CONVERTER


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PROPORTIONAL SIGNALS

Simple Equation

Assume minimum voltage of 0 V.Vmax= maximum voltage of theanalog signal.

a= analog value.n= number of bits for digitalencoding.

2n= number of digital codesM= number of steps, (2n 1)

d= digital encoding.

Vmax

0 V

1..1 = 2n-1

0..0 = 0


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RESOLUTION:

The resolution of the converter indicates the number

of discrete values it can produce over the range ofanalog values .

Or the smallest possible change in output voltage.

For example, an ADC with a resolution of 8 bits can

be mentioned to have a resolution of 0.00390625V(1/ 28).

BASICS OF A/D CONVERTER


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RESOLUTION

Let n = 2

M = 2n 1

3 steps on the digital scaled0= 0 = 0b00dVmax= 3 = 0b11

r, resolution: smallestanalog change resultingfrom changing one bit.

Vmax

0 V

3=11

2=10

1=01

0=00

r

3=11

2=10

1=01

0=00


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BASICS OF A/D CONVERTER

ACCURACY:

Accuracy of a A/D converter is the measure of thedifference between the actual output voltage andthe expected output voltage.


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ACCURACY

To improve the accuracy of A/D conversion:

Increasing the resolution which improves theaccuracy in measuring the amplitude of analogsignal.

Increasing the sampling rate which increases themaximum frequency that can be measured.


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ACCURACY


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TYPES OF A/D CONVERTERS

Simultaneous (Flash ADC).

Counter ADC.

Successive approximation ADC.

Tracking ADC.

Dual slope ADC.

Sigma delta ADC.


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SUCCESSIVE APPROXIMATION A/DCONVERTER


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WORKING

Uses a control logic unit that controls the operationof SAR.

Uses Successive Approximation Register(SAR)

which supplies an approximate digital code to DAC. Uses a comparator to compare the output of

DAC(Vref) and the given input(Vin).

The digital output from SAR has a value equal to the

given analog input.


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PROCESS


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PROCESS


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EXAMPLE PROBLEM

PROBLEM STATEMENT:

Successive Approximation ADC.

4-bit or 0.0625V resolution.Vin=1Volts.

Find digital value of Vin.


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EXAMPLE PROBLEM

Calculation of the state MSB:

Compare Vin= 1V and Vref= 8V(1000).

1V < 8V,MSB is turned OFF.MSB = 0.

Turn the next bit to 1.


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Calculation of the state MSB1:

Compare Vin and Vref. 1V and4V (0100). 1V< 4V, MSB1 is turned OFF.

MSB1 = 0.Turn the next bit to 1.

EXAMPLE PROBLEM


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EXAMPLE PROBLEM


Compare Vin and Vref. 1V and 2V (0010). 1V< 2V, MSB2 is turned OFF.

MSB2 = 0.Turn the next bit to 1.


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EXAMPLE PROBLEM


Compare Vin and Vref. 1V and1V (0001). 1V=1V, MSB3 is turned ON.

MSB3 = 1.


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ANSWER

oMSB = 0.

oMSB1 = 0.

oMSB2 = 0.

oMSB3 = 1.

So,

The digital value of Vin = 0001.


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Power taken is less. Moderate speed of operation.

Working on higher sampling rates.

It has only digital parts which makes itcomfortable with digital systems.

ADVANTAGES

DISADVANTAGE

ADCs with higher resolution will work

slower.


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APPLICATIONS

Thermocouples.

Strain gauge.

Pressure transducers.

Digital music recording.

Digital speed meter.


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pras DE .pptx