Transcript Digital Information

Analog to Digital Data Conversion
Analog vs. Digital



Computers use
digital information
Signals are
continuous analog
waveforms
Digital information
can be encoded in
the analog signal
Kin 304 Fall 2013
Modulation




Digital information
coded on a high
frequency carrier signal
AM -Amplitude
Modulation
FM – Frequency
Modulation
PM – Phase
Modulation
A to D
Digital Information
BIT = BINARY DIGIT
– either 1 or 0, high or low, yes or no
 Decimal = Base of 10

A to D
Base of 10
2543
1000
100 10
1
103
102 101
100
2
5
4
3
Kin 304 Fall 2013
Binary - Base of 2
41
32
16
8
4
2
1
5
2
4
2
3
2
2
2
1
2
0
2
1
0
1
0
0
1
Kin 304 Fall 2013
Bits & Bytes

Bit = Binary Digit

Byte = 8 Bits, 28 or 256 combinations

1 Kilobyte (KB) = 210 = 1024 bytes

1 Megabyte (MB) = 220 = 1,048,576 bytes

1 Gigabyte (GB) = 230 = 1,073,741,824 bytes

1 Terabyte (TB) = 240 = 1,099,511,627,776 bytes
A to D
Components for A/D Conversion
Measurable Quantity
 Measurement Device
 Analog Signal

–
Transducers
 transforms
–
one form of energy to another form
Electrodes
 sense
A to D
biological signals
Components for A/D Conversion

Analog Conditioning
» Electronic circuitry to modify the signal
before it enters the computer for digitization.
–amplification
–filtering
–integration
Components for A/D Conversion

A/D Conversion board + software
 Necessary to digitize the analog
signal
 Sample the analog signal at a set
frequency and store it as binary
information
Functions of A/D Board
Sampling
–
–
Analog signal is sampled by switching at a set frequency
Nyquist rule: at least twice frequency of signal to avoid aliasing
Voltage

Time
A to D
Signal Alias
Voltage
(sampling frequency too low)
Time
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Functions of A/D Board
Quantitization
Number of levels of voltage determined by the
number of bits in conversion:
The number of bits used to represent each
conversion effects how many possible different
values can be resolved from the converter...
# of Bits
Possible # of Values
1
2
2
4
8
256
12
4096
Encoding
Assigning a digital code
A to D
Resolution
 Resolution
of an A/D converter
 A measure of the smallest amplitude
value as a percent of full scale to
which a quantity can be determined
A to D
Voltage Range
Common ranges are:
-10v to +10v,
-1v to +1v,
-100mv to +100mv
A to D
Resolution Calculation
12 bit converter, -10v to +10v
-10v to +10v = 20 v
12 bit resolution = 4096 possible values
20v / 4096 = 0.00488v per bit (4.88 mv per bit)
A to D
A/D Software
 Require
A/D board compatible
control software
 LABVIEW
–
LABoratory Virtual Instrument
Engineering Workbench
 MATLAB
A to D