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Title: Digital Techniques
Description: Detailed about Digital techniques

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 A function that conveys information, generally about

the state or behavior of a physical system
...

 There are two types of signal
...

 Directly measurable quantities in terms of some other
quantity
...

Examples:
 Thermometer – mercury height rises as temperature rises
...

 Stereo – Volume increases as you turn the knob
...

 have only two states
...
“1” can be on, “0” can be off
...
So,

no common format
...

 High immunity to interference
...


of Signal
...


 Easier and efficient to multiplex

 Inflexible operation as compared to

several digital signals
...

 Flexible operation of the system

Digital operations
...


 Increased system complexity as every

 Storage difficult and costly
...


 Example:

A digital thermostat in a room displays a temperature of 72
...
482
...


 An analog signal can be any time-varying signal
...

 They can be periodic (repeating) or non-periodic
...

 Note that this square wave is not a digital signal because its minimum

value is negative
...
A

logic level is a voltage level that represents a defined digital state
...

 Their minimum value must be 0 volts, and their maximum
value must be 5 volts
...

 The time the signal is high (tH) can vary anywhere from 1% of
the period to 99% of the period

 Amplitude: For digital signals, this will ALWAYS be 5 volts
...
(seconds)
 Frequency: A measure of the number of occurrences of the signal







per second
...

Time Low (tL): The time the signal is at 0 v
...

Rising Edge: A 0-to-1 transition of the signal
...


Amplitude

Falling Edge

Time
High
(tH)

Time
Low
(tL)

Rising Edge

Period (T)

Frequency:
F

1
Hz
T

DutyCycle 

tH
 100%
T

 Not Accurate

 Increased system complexity
 Increased functional bandwidth

Because of the increasing use of digital computers in both data
processing and automatic control system, digital electronics has a
greater importance
...

 To process analog signals by digital means, it is first necessary
to convert them into digital form, that is, to convert them to a
sequence of numbers having finite precision
...


 3 Step process: Sampling, Quantization, coding

 Conversion of a continuous-time signal into a discrete- time
signal obtained by taking "samples" of the continuous-time
signal at discrete-time instants
...
As we see in the second picture, evaluating the signal
more often more accurately depicts the ADC signal
...

Higher no
...

 The value of each signal sample is represented by a value
selected from a finite set of possible values
...

 Is Amplitude discretization

 2 possible values



1 bit



2 bits  4 possible values



8 bits  256 possible values



16 bits  65356 possible values
:



:

N bits  2N possible values

} Quantization noise









 Each discrete value in a
quantization process is
represented by a b-bit
binary sequence
 Assigning a digital word
or number to each state
and matching it to the
input signal

Output
States

Output Binary
Equivalent

0

000

1

001

2

010

3

011

4

100

5

101

6

110

7

111

Xa(t)

Sampler

Analog
Signal

0101

X(n)

Xq(n)

Quantizer

Discretetime Signal

Quantized
Signal

Coder

Digital
Signal

 Microphones - take your voice varying pressure waves in the






air and convert them into varying electrical signals
Strain Gages - determines the amount of strain (change in
dimensions) when a stress is applied
Thermocouple – temperature measuring device converts
thermal energy to electric energy
Voltmeters
Digital Multimeters

 There are two ways to best improve accuracy of A/D

conversion:
 Increasing the sampling rate which increases the maximum

frequency that can be measured
...
(many levels
assignment in quantization process)

x [n]

DAC

Analog
filter

x(t)


Title: Digital Techniques
Description: Detailed about Digital techniques