365DIGI2 - Digital Data Acquisition Data Representation -...

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Slide 1 Digital Data Acquisition Data Representation - Digital vs. Analog Analog-to-Digital Conversion Number Systems (Binary Numbers) Sampling & Aliasing
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Slide 2 Data Representation - Digital vs. Analog Digital : 1s and 0s, (1001 1011) 2 Advantages Disadvantages Analog : 3.141592687. .., 1/3 Advantages Disadvantages
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Slide 3 Analog-to-Digital Conversion Converts analog voltages to binary integers. ADC Analog Voltage Binary Integers (0s & 1s) Sampling -1.5 -1 -0.5 0 0.5 1 1.5 012345678 Time Voltage
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Slide 4 Analog-to-Digital Conversion ADC calibration Calibration Curve ( 3 bit ADC) 0 1 2 3 7 6 5 4 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 Analog Voltage Integer Code
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Slide 5 Input Range – Unipolar: ( 0, V ADCMAX ) – Bipolar: ( -V ADCMAX , +V ADCMAX ) (Nominal Range) Clipping : If |V IN | > |V ADCMAX |, then |V OUT | = |V ADCMAX | Analog-to-Digital Conversion time V ADCMAX -V ADCMAX
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Slide 6 Quantization Interval ( Q ) n bit ADC, the input range is divided into 2 n -1 intervals. –3 b i t ADC : Analog-to-Digital Conversion Q VV n = MAX min 21 0 1 2 3 7 6 5 4 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 Analog Voltage Integer Code 0 1 2 3 7 6 5 4 2 1.5 1.0 .5 0.0 0.5 1.0 1.5 Analog Voltage Integer Code
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Slide 7 Voltage to Integer Code n bit ADC Analog-to-Digital Conversion Code Round = VV Q IN ADC min V ADCmin V ADCMAX Q Voltage: Code: 2 n 1 0 V IN 2 n 1 2 n 1 1 Positive Coding: Positive and Negative Coding: = V Q IN
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Slide 8 Voltage to Integer Code (cont.) Ex: 3 bit ADC, V ADCmin = 2 V and V ADCMAX = 1.5 V V IN = 1.25 V Q: Find the integer code for V IN using only positive integers and using both positive and negative integers. Analog-to-Digital Conversion
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Slide 9 Convert Code to Estimated Voltage V offset : voltage corresponding to code 0 Analog-to-Digital Conversion ⇒= × + Code $ VQ V IN offset V ADCmin V ADCMAX Q Voltage: Code: 2 n 1 0 $ V IN Code 2 n 1 1 0 2 n 1
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This note was uploaded on 04/23/2011 for the course ME 365 taught by Professor Merkle during the Spring '07 term at Purdue University.

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365DIGI2 - Digital Data Acquisition Data Representation -...

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