Analog to Digital Data Conversion

Kin 304 Fall 2013

Analog vs. Digital

Computers use digital information

Signals are continuous analog waveforms

Digital information can be encoded in the analog signal

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Modulation

Digital information coded on a high frequency carrier signal

AM -Amplitude Modulation

FM – Frequency Modulation

PM – Phase Modulation

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Digital Information

BIT = BINARY DIGIT – either 1 or 0, high or low, yes or no

Decimal = Base of 10

Kin 304 Fall 2013

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

25 24 23 22 21 20

1 0 1 0 0 1

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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

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Components for A/D Conversion

Measurable QuantityMeasurement DeviceAnalog Signal

– Transducerstransforms one form of energy to another form

– Electrodessense biological signals

Analog Conditioning» Electronic circuitry to modify the signal

before it enters the computer for digitization.– amplification– filtering– integration

Components for A/D Conversion

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

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Time

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e

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Signal Alias (sampling frequency too low)

Time

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e

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Functions of A/D Board

QuantitizationNumber 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 25612 4096

EncodingAssigning a digital code

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Resolution

Resolution of an A/D converterA measure of the smallest amplitude

value as a percent of full scale to which a quantity can be determined

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Voltage Range

Common ranges are:

-10v to +10v, -1v to +1v, -100mv to +100mv

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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)

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A/D Software

Require A/D board compatible control software

LABVIEW– LABoratory Virtual Instrument

Engineering WorkbenchMATLAB