1. In presenting Order: Josh Navikonis Moiz H Mike Hochman Brian Post Analog-Digital Converters ME 6405 9/29/2009

2. Agenda  Introduction to ADC  Types of ADC  Characteristics of ADC in MC9S12C  Application and Selection of ADC

3. Introduction of ADC  What is ADC?  Why is ADC important?  How does it work?

4. What is ADC?  ADC (Analog to Digital Converter) is an electronic device that converts a continuous analog input signal to discrete digital numbers (binary)  Analog  Real world signals that contain noise  Continuous in time  Digital  Discrete in time and value  Binary digits that contain values 0 or 1

5. Why is ADC Important?  All microcontrollers store information using digital logic  Compress information to digital form for efficient storage  Medium for storing digital data is more robust  Digital data transfer is more efficient  Digital data is easily reproducible  Provides a link between real-world signals and data storage

6. How ADC Works 2 Stages:  Sampling  Sample-Hold Circuit  Aliasing  Quantizing and Encoding  Resolution Binary output

7. Sampling  Reduction of a continuous signal to a discrete signal  Achieved through sampling and holding circuit  Switch ON – sampling of signal (time to charge capacitor w/ V in )  Switch OFF - voltage stored in capacitor (hold operation)  Must hold sampled value constant for digital conversion Response of Sample and Hold Circuit Simple Sample and Hold Circuit

8. Sampling  Sampling rate depends on clock frequency  Use Nyquist Criterion  Increasing sampling rate increases accuracy of conversion  Possibility of aliasing Sampling Signal: Sampling Period: Nyquist Criterion:

9. Aliasing  High and low frequency samples are indistinguishable  Results in improper conversion of the input signal  Usually exists when Nyquist Criterion is violated  Can exist even when:  Prevented through the use of Low-Pass (Anti-aliasing) Filters

10. Quantizing and Encoding  Approximates a continuous range of values and replaces it with a binary number  Error is introduced between input voltage and output binary representation  Error depends on the resolution of the ADC

11. Resolution  Maximum value of quantization error  Error is reduced with more available memory Example: V range =Input Voltage Range n= # bits of ADC Resolution

12.  Increase in resolution improves the accuracy of the conversion Minimum voltage step recognized by ADC Analog Signal Digitized Signal- High Resolution Digitized Signal- Low Resolution

13. Flash A/D Converter Successive Approximation A/D Converter Example of Successive Approximation Dual Slope A/D Converter Delta – Sigma A/D Converter Types of A/D Converters Presenter : Moiz H

14. Elements of a Flash A/D Converter Encoder Comparator

15. FLASH A/D CONVERTER 3 Bit Digital Output Resolution 2 3 -1 = 7 Comparators

16. Flash A/D Converter Contd. Pros Fastest (in the order of nano seconds) Simple operational theory Speed is limited only by gate and comparator propagation delay Each additional bit of resolution requires twice the number of comparators Expensive Prone to produce glitches in the output Cons

17. Integrator Elements of Dual-Slope ADC

18. Dual-Slope ADC *

19. Elements of the Successive Approximation ADC Takes in a Combination of Bits Successive Approximation Register Digital to Analog Converter

20. SUCESSIVE APPROXIMATION A/D CONVERTER

21. Example Show the timing waveforms that would occur in SAR ADC when converting an analog voltage of 6.84V to 8-bit binary, assume that the full scale input voltage of the DAC is 10V. Vref = 10 V Vin = 6.84 V

22. DAC InputDAC Vout Cumulative Voltage D75.0000 D62.50007.5000 D51.25008.7500 D40.62509.3750 D30.31259.6875 D20.156259.84375 D10.0781259.921875 D00.03906259.9609375 6.84 V 5 7.5 6.25 6.875 6.5625 6.71875 6.796875 6.8359375 5 7.5 6.25 6.875 6.5625 6.71875 6.796875 6.8359375

23. Dual Slope A/D Converter Contd. Pros High accuracy Fewer adverse affects from noise Slow Accuracy is dependent on the use of precision external components Cons

24. Delta-Sigma ADC

25. #1 Delta-Sigma Modulator Delta-Sigma ADC contd.

26. #2 Digital Filter Delta-Sigma ADC contd. Decimator

27. Sigma-Delta A/D Converter Contd. Pros High Resolution No need of precision components Slow due to over sampling Good for low bandwidth Cons

28. TypeSpeed(relative)Cost(Relative) Dual SlopeSlowMed FlashVery fastHigh Successive approxMedium fastLow Sigma-DeltaSlowLow ADC Comparison

29. ATD10B8C on MC9S12C32  Presented by:  Michael Hochman

30. MC9S12C32 Block Diagram

31. ATD10B8C Block Diagram

32. ATD10B8C Key Features  Resolution  8/10 bit (manually chosen)  Conversion Time  7 usec, 10 bit  Successive Approximation ADC architecture  8-channel multiplexed inputs  External trigger control  Conversion modes  Single or continuous sampling  Single or multiple channels

33. ATD10B8C External Pins  12 external pins  AN7 / ETRIG / PAD7 Analog input channel 7 External trigger for ADC General purpose digital I/O  AN6/PAD6 – AN0/PAD0 Analog input General purpose digital I/O  V RH, V RL High and low reference voltages for ADC  V DDA, V SSA Power supplies for analog circuitry

34. ATD10B8C Registers  6 Control Registers ($0080 - $0085)  Configure general ADC operation  2 Status Registers ($0086, $008B)  General status information regarding ADC  2 Test Registers ($0088 - $0089)  Allows for analog conversion of internal states  16 Conversion Result Registers ($0090 - $009F)  Formatted results (2 bytes)  1 Digital Input Enable Register ($008D)  Convert channels to digital inputs  1 Digital Port Data Register ($008F)  Contains logic levels of digital input pins

35. Control Register 2

36. Control Register 3

37. Control Register 4

38. Control Register 5

39. Single Channel Conversions

40. Multi-channel Conversions

41. Status Register 0

42. Status Register 1

43. Results Registers

44. ATD Input Enable Register

45. Port Data Register

46. Setting up the ADC

47. Applications For ADC  What are some applications for Analog to Digital Converters?  Measurements / Data Acquisition  Control Systems  PLCs (Programmable Logic Controllers)  Sensor integration (Robotics)  Cell Phones  Video Devices  Audio Devices

48. Measurements / Data Acquisition  The sampling of the real world to generate data that can be manipulated by a computer  (DSP) Digital Signal Processing first requires a digital signal  Eg. Analysis of data from weather balloons by the National Weather Service What is Data AcquisitionNI X-Series Data Acquisition Card

49. Control Systems S/H & ADC Digital CPU Controller D/A & Hold Plant Transducer Clock Digital Control System + - R Y tt ee* Controller 0010 0101 0011 1011 ∆t e*(∆t) 1001 0010 1010 0101 ∆t u*(∆t) e e*(∆t) u*(∆t) u

50. The Old Way…. Analog Computers Comdyna GP6

51. The New Way tt ee* Controller 0010 0101 0011 1011 ∆t e*(∆t) 1001 0010 1010 0101 ∆t u*(∆t) ADC Analog Input D/A Analog Output

52. Programmable Logic Controllers  PLCs are the industry standard for automation tasks including:  Motion Control  Safety Systems  designed for:  multiple inputs and output arrangements  extended temperature ranges  immunity to electrical noise  resistance to vibration and impact  Most I/O are Boolean, however most PLC systems have an analog I/O module ADC in PLCsRockwell PLC Analog I/O Module

53. Sensor Integration (Robotics)  Many robots use microprocessors  ADC allows robots to interpret environmental cues and compensate  If the algorithm needs to be changed it’s a simple matter of modifying the code  Analog control systems require a complete circuit redesign

54. Cell Phones  Digital signals can be easily manipulated  Digital phones convert your voice into binary information and then compress it  This compression allows between three and 10 digital calls to occupy the space of a single analog call.  The analog-to-digital and digital-to- analog conversion chips translate the outgoing audio signal from analog to digital and the incoming signal from digital back to analog Why Digital?

55. Audio Devices  ADCs are integral to current music reproduction technology  They sample audio streams and store the digital data on media like compact disks  The current crop of AD converters utilized in music can sample at rates up to 192 kilohertz  Sound Cards ExamplesADC From Sound Card

56. Video Devices  Analog video and audio signals are converted to digital signals for display to user  Slingbox converts analog input stream and rebroadcasts it across the internet in digital form  CCDs use ADCs to process image data TV Tuners

57. Selection of an ADC  Important Considerations:  Input Type – Differential or Single Ended  Resolution - Most Important  Scaling - allows the user to divide or multiply the input voltage to more closely match the full scale range of the ADC  Sample Rate - The sample rate must be at least twice the frequency the you are measuring, but 5 times is much better  Channel Scan Rate - The channel scan rate is the maximum rate that the ADC can select a new channel and make a measurement. many ADCs have a relatively slow scan rate (when compared to the sample rate.) Eg. To achieve a sample rate of 600Hz on three channels, you will need a channel scan rate of at least 1.8kHz

58. Example: Selecting an ADC  We want to digitize a vibration signal measured by an accelerometer with the following characteristics (PCB 301A10):  Sensitivity: (±2.0%) 100 mV/g  Measurement Range: ±50 g pk  Frequency Range: (±5%) 0.5 to 10000 Hz  Select a satisfactory Analog to Digital Converter….

59. Example Continued  Desired Signal:  Sensitivity: (±2.0%) 100 mV/g  Measurement Range: ±50 g pk  Frequency Range: (±5%) 0.5 to 10000 Hz  Resolution:  Minimum Sampling Freq:  Ideal Sampling Freq: Solution

60. Choosing AD7892  From Analog Devices:  The AD7892 is a high speed, low power, 12-bit A/D converter that operates from a single +5 V supply. The part contains a 1.47 µs successive approximation ADC, an on-chip track/hold amplifier, an internal +2.5 V reference and on- chip versatile interface structures that allow both serial and parallel connection to a microprocessor. The part accepts an analog input range of ±10 V or ±5 V. Overvoltage protection on the analog inputs for the AD7892-1 and AD7892-3 allows the input voltage to go to ±17 V or ±7 V respectively without damaging the ports.

61. References  Cetinkunt, Sabri. Mechatronics 2007  www.me.gatech.edu/mechatronics_course  en.wikipedia.org/  www.engineer.tamuk.edu/  www.scm.tees.ac.uk  Bishop, Ron. Basic Microprocessors and the 6800  MC912SC Family Data Sheet  MC912SC Reference Manual  MC912SC Programming Reference Guide