1. ECE 2799 Electrical and Computer Engineering Design ANALOG to DIGITAL CONVERSION Prof. Bitar Last Update: 11-12-12

2. ADC Symbol (Parallel Output) S. J. Bitar - 2010 ADC N Bits D0D0 DNDN A IN

3. Important ADC Parameters Resolution Resolution Accuracy Accuracy Conversion Time Conversion Time S. J. Bitar - 2010

4. 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 = 256 2 N = 2 8 = 256 Voltage per Step Voltage per Step ΔV = V FullScaleRange / 2 N ΔV = V FullScaleRange / 2 N = 5V / 256 = 5V / 256 = 19.53125 mV = 19.53125 mV S. J. Bitar - 2010

5. Conversion Table (for ΔV = 1LSB = 5V / 256 = 19.53125 mV ) S. J. Bitar - 2010 Dec.HexBinaryV (mV) 0000000 0.000 1010000 000119.531 2020000 001039.063. 128. 80. 1000 0000. 2.500 V. 255FF1111 4.980 V Q: How would you digitize 20mV?

6. Voltage to Binary Transfer Characteristic S. J. Bitar - 2010 Courtesy: Analog Devices AD7819 Datasheet

7. 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, 19.531mV / 2 = 9.766mV 19.531mV / 2 = 9.766mV As a percentage of V FSR, that would be, As a percentage of V FSR, that would be, 9.766mV / 5.000 x 100 = 0.195% 9.766mV / 5.000 x 100 = 0.195% S. J. Bitar - 2010

8. 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 - 2010

9. 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 - 2010

10. 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 - 2010

11. AD7819 8-Bit Parallel DAC S. J. Bitar - 2010

12. AD7819 Block Diagram S. J. Bitar - 2010

13. AD7819 Pin Descriptions S. J. Bitar - 2010

14. Package Pin Assignments S. J. Bitar - 2010

15. AD7819 Converter Operation S. J. Bitar - 2010

16. AD7819 Typical Circuit S. J. Bitar - 2010

17. AD7819 Equivalent Analog Input Model S. J. Bitar - 2010

18. AD7819 DC Acquisition Time S. J. Bitar - 2010

19. AD7819 Transfer Characteristic S. J. Bitar - 2010

20. AD7819 Microcontroller Interfacing S. J. Bitar - 2010

21. AD7819 Timing and Control S. J. Bitar - 2010

22. 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 - 2010

24. Conversion Formula S. J. Bitar - 2010

25. Analog Multiplexer S. J. Bitar - 2010

26. Sample Timing S. J. Bitar - 2010

27. Analog Input Model S. J. Bitar - 2010

28. Conversion Mode Summary S. J. Bitar - 2010

29. Conversion State Diagram S. J. Bitar - 2010

30. Transferring Data to Memory S. J. Bitar - 2010

31. Interrupt Driven Conversion S. J. Bitar - 2010

32. ADC Registers S. J. Bitar - 2010

33. Example: Control Register 1 S. J. Bitar - 2010

34. Example: Input Channel Select S. J. Bitar - 2010