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 25 24 23 22 21 20 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 biological signals A to D
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 A to D
Signal Alias (sampling frequency too low) A to D
Functions of A/D Board Quantitization Encoding 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 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