ECE 2799 Electrical and Computer Engineering Design ANALOG to DIGITAL CONVERSION Prof. Bitar Last Update:

ADC Symbol (Parallel Output) S. J. Bitar ADC N Bits D0D0 DNDN A IN

Important ADC Parameters Resolution Resolution Accuracy Accuracy Conversion Time Conversion Time S. J. Bitar

ADC Resolution Number of Bits Number of Bits Example: N=8 Bits Example: N=8 Bits Number of Discrete Levels Number of Discrete Levels 2 N = 2 8 = N = 2 8 = 256 Voltage per Step Voltage per Step ΔV = V FullScaleRange / 2 N ΔV = V FullScaleRange / 2 N = 5V / 256 = 5V / 256 = mV = mV S. J. Bitar

Conversion Table (for ΔV = 1LSB = 5V / 256 = mV ) S. J. Bitar Dec.HexBinaryV (mV) V. 255FF V Q: How would you digitize 20mV?

Voltage to Binary Transfer Characteristic S. J. Bitar Courtesy: Analog Devices AD7819 Datasheet

Accuracy: Quantization Error Quantization Error is often equal to ½ the Least-Significant-Bit voltage. Quantization Error is often equal to ½ the Least-Significant-Bit voltage. In our example, that would be, In our example, that would be, mV / 2 = 9.766mV mV / 2 = 9.766mV As a percentage of V FSR, that would be, As a percentage of V FSR, that would be, 9.766mV / x 100 = 0.195% 9.766mV / x 100 = 0.195% S. J. Bitar

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.) 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. Depends greatly on the architecture of the ADC. There are different types. SAR (Successive Approximation Register) SAR (Successive Approximation Register) Sigma-Delta Sigma-Delta Flash Flash S. J. Bitar

How do You Choose ? Well, how often do you need to sample your analog waveform, if you want to reproduce it accurately? Well, how often do you need to sample your analog waveform, if you want to reproduce it accurately? Nyquist Rate (minimum) Nyquist Rate (minimum) For audio, typically 44.1 kSPS is used. For audio, typically 44.1 kSPS is used. That’s 22.67µsec per sample, so the conversion time has to be faster than that! That’s 22.67µsec per sample, so the conversion time has to be faster than that! S. J. Bitar

A Look at Two ADC’s Analog Devices AD7819 Analog Devices AD7819 Texas Instruments MSP430xx series microcontrollers with built-in ADC’s Texas Instruments MSP430xx series microcontrollers with built-in ADC’s S. J. Bitar

AD Bit Parallel DAC S. J. Bitar

AD7819 Block Diagram S. J. Bitar

AD7819 Pin Descriptions S. J. Bitar

Package Pin Assignments S. J. Bitar

AD7819 Converter Operation S. J. Bitar

AD7819 Typical Circuit S. J. Bitar

AD7819 Equivalent Analog Input Model S. J. Bitar

AD7819 DC Acquisition Time S. J. Bitar

AD7819 Transfer Characteristic S. J. Bitar

AD7819 Microcontroller Interfacing S. J. Bitar

AD7819 Timing and Control S. J. Bitar

MSP430xx ADC Features Maximum conversion rate 200 ksps Maximum conversion rate 200 ksps Monotonic 10-bit converter Monotonic 10-bit converter Internal sample-and-hold Internal sample-and-hold Timer control option Timer control option Optional on-chip reference (1.5 V or 2.5 V) Optional on-chip reference (1.5 V or 2.5 V) Up to 12 inputs (depends on chip) Up to 12 inputs (depends on chip) Internal temp reference Internal temp reference Selectable clock source Selectable clock source Multiple conversion modes Multiple conversion modes Auto-conversion storage / data transfer modes Auto-conversion storage / data transfer modes S. J. Bitar

Conversion Formula S. J. Bitar

Analog Multiplexer S. J. Bitar

Sample Timing S. J. Bitar

Analog Input Model S. J. Bitar

Conversion Mode Summary S. J. Bitar

Conversion State Diagram S. J. Bitar

Transferring Data to Memory S. J. Bitar

Interrupt Driven Conversion S. J. Bitar

ADC Registers S. J. Bitar

Example: Control Register 1 S. J. Bitar

Example: Input Channel Select S. J. Bitar