Analog To Digital Convert

ADC &DAC

Ishraq Madi JboorNoor Al_huda Mahir

An analog signal is a continuous signal that contains time-varying quantities, such as temperature or speed, with infinite possible values in betweenAn analog signal can be used to measure changes in some physical phenomena such as light, sound, pressure, or temperature.

Sine WaveRandom- PeriodicAnalog :-

Analog SignalsContinuousInfinite range of valuesMore exact values, but more difficult to work withDigital SignalsDiscreteFinite range of values Not as exact as analog, but easier to work withExample: A digital thermostat in a room displays a temperature of 72. An analog thermometer measures the room temperature at 72.482. The analog value is continuous and more accurate, but the digital value is more than adequate for the application and significantly easier to process electronically.

Advantages:1-Major advantages of the analog signal is infinite amount of data.2-Density is much higher.3-Easy processing.Disadvantages:1-Unwanted noise in recording.2-If we transmit data at long distance then unwanted disturbance is there.3-Generation loss is also a big con of analog signals.

Is a type ofsignalthat can take on a set ofdiscretevalues (aquantizedsignal)Digital signals can represent a discrete set of values using any discrete set ofwaveforms .. And we can represent it like (0 or 1) ,( on or off ).. etc

Digital -:

Digital signals can be optical, electrical, acoustic, or others. Digital signals are present in all digital electronics, notably computing equipment and telecommunications.Digital signals must have a finite set of possible values. The number of values in the set can be anywhere between two and a-very-large-number-thats-not-infinity. Most commonly digital signals will be one oftwo values like either 0V or 5V. Timing graphs of these signals look likesquare waves

Or a digital signal might be a discrete representation of an analog waveform. Viewed from afar, the wave function below may seem smooth and analog, but when you look closely there are tiny discretestepsas the signal tries to approximate values.

Thats the big difference between analog and digital waves. Analog waves are smooth and continuous, digital waves are stepping, square, and discrete.Working with electronics means dealing with both analog and digital signals, inputs and outputs. Our electronics projects have to interact with the real, analog world in some way, but most of our microprocessors, computers, and logic units are purely digital components. These two types of signals are like different electronic languages; some electronics components are bi-lingual, others can only understand and speak one of the two.

Quantizing - breaking down analog value is a set of finite statesEncoding - assigning a digital word or number to each state and matching it to the input signal ADCThe number of possible states that the converter can output is:N=2n (Where n is the number of bits in the AD converter)Analog quantization size:Q= (V max -V min)/N Quantizing -: There are two step Process-:

Example: For a 3 bit A/D converter, you have 0-10V signals. Separate them into a set of discrete statesSol: N=23=8 Q= (10V 0V)/8 = 1.25V

QuantizationOutput StatesDiscrete Voltage Ranges (V)00.00-1.2511.25-2.5022.50-3.7533.75-5.0045.00-6.2556.25-7.5067.50-8.7578.75-10.0

Encoding Output StatesOutput Binary Equivalent00001001201030114100510161107111

Here we assign the digital value (binary number) to each state for the computer to read.

It is a process of taking a sufficient number of discrete values at point on a waveform that will define the shape of waveform.The more samples you take, the more accurately you will define the waveform.It converts analog signal into series of impulses, each representing amplitude of the signal at given point.

Flash ADC Digital-Ramp/Dual slope/Counter slope ADCSuccessive Approximation ADCSampling -:

Types of A/D convertor :-

Consists of a series of comparators, each one comparing the input signal to a unique reference voltage. The comparator outputs connect to the inputs of a priority encoder circuit, which produces a binary output3 bit Flash ADC Circuit

Flash ADC :-

Simplest in terms of operational theoryMost efficient in terms of speed, very fast Limited only in terms of comparator and gate propagation delaysLower resolution ExpensiveFor each additional output bit, the number of comparators is doubledAdvantages :-

Disadvantages :-

Dual Slope ADCAlso known as Counter-Ramp or Digital Ramp ADC, A dual slope ADC is commonly used in measurement instruments

Dual Slope ADC circuit

Successive approximation ADCMuch faster than the digital ramp ADC because it uses digital logic to converge on the value closest to the input voltage.

A comparator and a DAC are used in the process

Successive approximation ADC circuit

out put

ADC Resolution Comparison0510152025

Successive Approx Flash Dual SlopeResolution (Bits)

TypeSpeed (relative)Cost (relative)Dual SlopeSlowMedFlashVery Fast HighSuccessive ApproxMedium FastLow

Digital-to-analog conversionis a process in which signals having a two defined levels or states (digital (binary)) are converted into signals having a theoretically infinite number of states (analog (current, voltage, or electric charge)). A common example is the processing, by amodem, of computer data into audio-frequency (AF) tones that can be transmitted over atwisted pairtelephone line. The circuit that performs this function is adigital-to-analog converter (DAC).

(1-2)DAC

binary weighted resistor DAC :-Output of each bit of the register will depend on whether a 1 or a 0 is stored in that positionExample ... 0 the output will be 0 volt1 the output will be 5 voltresistance R is inversely proportional to binary weight of each digit

Buffering the Resistor :-all input currents sum at S and go through Rf(Vo = -If Rf)

Vo = -If Rf =-(I1+I2+I3+I4)Rf

Digital/analog example :-calculate the output voltage for an input code word 0110 if a logic 1 is 10V and logic 0 is 0Vand R = Rf =1kI=V/RI1=I4=0I2=10V/2R = 10/2K= 5 mAI3=10V/4R=10/4K=0.25 mAVo = -If Rf = -(0.0052) 1000 = -5.2 volts

Basically, digital-to-analog conversion is the opposite of analog-to-digital conversion. In most cases, if ananalog-to-digital converter (ADC)is placed in a communications circuit after a DAC, the digital signal output is identical to the digital signal input. Also, in most instances when a DAC is placed after an ADC, the analog signal output is identical to the analog signal input.

Signal transformation life cycle

The final step

There is a huge deferent between these signals :AnalogDigitalSignalAnalog signal is a continuous signal which represents physical measurements.Digital signals are discrete time signalsWavesDenoted by sine wavesDenoted by square wavesRepresentationUses continuous range of values to representinformationUses discrete or discontinuous values to represent informationData transmissionsSubjected to deterioration by noise during transmission and write/read cycle.Can be noise-immune without deterioration during transmission and write/read cycle

MemoryStored in the form of wave signalStored in the form of binary bitResponse to NoiseMore likely to get affected reducing accuracyLess affected since noise response are analog in natureFlexibilityAnalog hardware is not flexible.Digital hardware is flexible in implementation.UsesCan be used in analog devices only. Best suited for audio and video transmission.Best suited for Computing and digital electronics.ApplicationsThermometerPCs, PDAsBandwidthAnalog signal processing can be done in real time and consumes less bandwidth.There is no guarantee that digital signal processing can be done in real time and consumes more bandwidth to carry out the same information.

PowerAnalog instrument draws large powerDigital instrument draws only negligible powerCostLow cost and portableCost is high and not easilyImpedanceLowHigh order of 100 megaohmErrorsAnalog instruments usually have a scale which is cramped at lower end and give considerable observational errors.Digital instruments are free from observational errors like parallax and approximation errors.ExampleHuman voice in air, analog electronic devices.opticalsComputers, CDs, DVDs, and other digital electronic devices.

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