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In presenting Order: Josh Navikonis Moiz H Mike Hochman Brian Post

Analog-Digital Converters. In presenting Order: Josh Navikonis Moiz H Mike Hochman Brian Post. ME 6405 9/29/2009. Agenda. Introduction to ADC Types of ADC Characteristics of ADC in MC9S12C Application and Selection of ADC. Introduction of ADC. What is ADC? Why is ADC important?

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In presenting Order: Josh Navikonis Moiz H Mike Hochman Brian Post

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  1. Analog-Digital Converters In presenting Order: Josh Navikonis Moiz H Mike Hochman Brian Post 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/ Vin) • 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 Vrange=Input Voltage Range n= # bits of ADC Example: Resolution

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

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

  15. FLASH A/D CONVERTER Resolution 23-1 = 7 Comparators 3 Bit Digital Output

  16. Flash A/D Converter Contd. Pros Cons • 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

  17. Elements of Dual-Slope ADC Integrator

  18. Dual-Slope ADC *

  19. Elements of the Successive Approximation ADC Successive Approximation Register Takes in a Combination of Bits 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. Vin = 6.84 V Vref = 10 V

  22. 5 5 7.5 7.5 6.25 6.25 6.875 6.875 6.5625 6.5625 6.71875 6.71875 6.796875 6.796875 6.8359375 6.8359375 6.84 V

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

  24. Delta-Sigma ADC

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

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

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

  28. ADC Comparison

  29. ATD10B8C on MC9S12C32 • Presented by: • Michael Hochman

  30. MC9S12C32Block 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 • VRH, VRL • High and low reference voltages for ADC • VDDA, VSSA • 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 What is Data Acquisition NI X-Series Data Acquisition Card • 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

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

  50. The Old Way…. Analog Computers Comdyna  GP6

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