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 V = V FullScaleRange / 2 N V = V FullScaleRange / 2 N = 5V / 256 = 5V / 256 = mV = mV S. J. Bitar Conversion Table (for V = 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 the Least-Significant-Bit voltage. Quantization Error is often equal to 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. Thats 22.67sec per sample, so the conversion time has to be faster than that! Thats 22.67sec per sample, so the conversion time has to be faster than that! S. J. Bitar A Look at Two ADCs Analog Devices AD7819 Analog Devices AD7819 Texas Instruments MSP430xx series microcontrollers with built-in ADCs Texas Instruments MSP430xx series microcontrollers with built-in ADCs 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