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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)