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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
A to D
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
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 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
A to D
Time
Vo
ltag
e
A to D
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
A to D
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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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)