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This resource provides a comprehensive overview of Analog to Digital Conversion (ADC) in Electrical and Computer Engineering. Key parameters such as resolution, accuracy, and conversion time are discussed. Effective methods to digitize analog signals are explained, along with practical examples, including the use of an 8-bit ADC and insights into different ADC architectures like SAR and Sigma-Delta. Learn about voltage-to-binary characteristics, quantization error, and how to select the right ADC based on application requirements.
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ECE 2799 Electrical and Computer Engineering Design ANALOG to DIGITAL CONVERSION Prof. Bitar Last Update: 04-08-11
ADC Symbol(Parallel Output) DN ADC AIN N Bits D0 S. J. Bitar - 2010
Important ADC Parameters • Resolution • Accuracy • Conversion Time S. J. Bitar - 2010
ADC Resolution • Number of Bits • Example: N=8 Bits • Number of Discrete Levels • 2N = 28 = 256 • Number of Steps (Intervals) • (2N-1) = 255 • Voltage per Step • ΔV = VFullScaleRange/ (2N-1) OR VFSR/ 2N • Method 1: ΔV = 5V / 255 = 19.608 mV • Method 2: ΔV = 5V / 256 = 19.531 mV S. J. Bitar - 2010
Conversion Table(for ΔV = 5V / 256 = 19.531 mV ) Q: How would you digitize 20mV? S. J. Bitar - 2010
Voltage to Binary Transfer Characteristic Courtesy: Analog Devices AD7819 Datasheet S. J. Bitar - 2010
Accuracy: Quantization Error • Quantization Error is often equal to ½ the Least-Significant-Bit voltage. • In our example, that would be, • 19.531mV / 2 = 9.766mV • As a percentage of VFSR, that would be, • 9.766mV / 5.000 x 100 = 0.195% S. J. Bitar - 2010
Conversion Time • The time required for the ADC to convert a stable analog input voltage to a binary number. (Implies the use of a S/H circuit.) • Depends greatly on the architecture of the ADC. There are different types. • SAR (Successive Approximation Register) • Sigma-Delta • Flash S. J. Bitar - 2010
How do You Choose ? • Well, how often do you need to sample your analog waveform, if you want to reproduce it accurately? • Nyquist Rate (minimum) • For audio, typically 44.1 kSPS is used. • That’s 22.67µsec per sample, so the conversion time has to be faster than that! S. J. Bitar - 2010
A Look at Two ADC’s • Analog Devices AD7819 • Texas Instruments MSP430xx series microcontrollers with built-in ADC’s S. J. Bitar - 2010
AD7819 8-Bit Parallel DAC S. J. Bitar - 2010
AD7819 Block Diagram S. J. Bitar - 2010
AD7819 Pin Descriptions S. J. Bitar - 2010
Package Pin Assignments S. J. Bitar - 2010
AD7819 Converter Operation S. J. Bitar - 2010
AD7819 Typical Circuit S. J. Bitar - 2010
AD7819Equivalent Analog Input Model S. J. Bitar - 2010
AD7819 DC Acquisition Time S. J. Bitar - 2010
AD7819Transfer Characteristic S. J. Bitar - 2010
AD7819 Microcontroller Interfacing S. J. Bitar - 2010
AD7819 Timing and Control S. J. Bitar - 2010
MSP430xx ADC Features • Maximum conversion rate 200 ksps • Monotonic 10-bit converter • Internal sample-and-hold • Timer control option • Optional on-chip reference (1.5 V or 2.5 V) • Up to 12 inputs (depends on chip) • Internal temp reference • Selectable clock source • Multiple conversion modes • Auto-conversion storage / data transfer modes S. J. Bitar - 2010
Conversion Formula S. J. Bitar - 2010
Analog Multiplexer S. J. Bitar - 2010
Sample Timing S. J. Bitar - 2010
Analog Input Model S. J. Bitar - 2010
Conversion Mode Summary S. J. Bitar - 2010
Conversion State Diagram S. J. Bitar - 2010
Transferring Data to Memory S. J. Bitar - 2010
Interrupt Driven Conversion S. J. Bitar - 2010
ADC Registers S. J. Bitar - 2010
Example: Control Register 1 S. J. Bitar - 2010
Example: Input Channel Select S. J. Bitar - 2010
