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Analog to Digital Converters (ADC)

Analog to Digital Converters (ADC). Ben Lester, Mike Steele, Quinn Morrison. Topics. Introduction Why? Types and Comparisons Successive Approximation ADC example Applications ADC System in the CML-12C32 Microcontroller.

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Analog to Digital Converters (ADC)

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  1. Analog to Digital Converters (ADC) Ben Lester, Mike Steele, Quinn Morrison

  2. Topics Introduction Why? Types and Comparisons Successive Approximation ADC example Applications ADC System in the CML-12C32 Microcontroller

  3. Analog systems are typically what engineers need to analyze. ADCs are used to turn analog information into digital data.

  4. Process Sampling, Quantification, Encoding

  5. Resolution, Accuracy, and Conversion time Resolution – Number of discrete values it can produce over the range of analog values; Q=R/N Accuracy – Improved by increasing sampling rate and resolution. Time – Based on number of steps required in the conversion process.

  6. Comparing types of ADCs Flash ADC Sigma-delta ADC Wilkinson ADC Integrating ADC Successive Approximation Converter

  7. Flash ADC Speed: High Cost: High Accuracy: Low

  8. Sigma-delta ADC Speed: Low Cost: Low Accuracy: High

  9. Wilkinson ADC Speed: High Cost: High Accuracy: High Wilkinson Analog Digital Converter (ADC) circuit schematic diagram

  10. Integrating ADC Speed: Low Cost: Low Accuracy: High

  11. Successive Approximation Converter Speed: High Cost: High Accuracy: High but limited

  12. Topics Introduction Why? Types and Comparisions Successive Approximation ADC example Applications ADC System in the CML-12C32 Microcontroller

  13. Successive Approximation ADC Example Mike Steele • Goal: Find digital value Vin • 8-bit ADC • Vin = 7.65 • Vfull scale = 10

  14. Successive Approximation ADC Example • Vfull scale = 10, Vin = 7.65 • MSB  LSB • Average high/low limits • Compare to Vin • Vin > Average  MSB = 1 • Vin < Average  MSB = 0 • Bit 7 • (Vfull scale +0)/2 = 5 • 7.65 > 5  Bit 7 = 1

  15. Successive Approximation ADC Example • Vfull scale = 10, Vin = 7.65 • MSB  LSB • Average high/low limits • Compare to Vin • Vin > Average  MSB = 1 • Vin < Average  MSB = 0 • Bit 6 • (Vfull scale +5)/2 = 7.5 • 7.65 > 7.5  Bit 6 = 1

  16. Successive Approximation ADC Example • Vfull scale = 10, Vin = 7.65 • MSB  LSB • Average high/low limits • Compare to Vin • Vin > Average  MSB = 1 • Vin < Average  MSB = 0 • Bit 5 • (Vfull scale +7.5)/2 = 8.75 • 7.65 < 8.75  Bit 5 = 0

  17. Successive Approximation ADC Example • Vin = 7.65 • MSB  LSB • Average high/low limits • Compare to Vin • Vin > Average  MSB = 1 • Vin < Average  MSB = 0 • Bit 4 • (8.75+7.5)/2 8.125 • 7.65 < 8.125  Bit 4 = 0

  18. Successive Approximation ADC Example • Vin = 7.65 • MSB  LSB • Average high/low limits • Compare to Vin • Vin > Average  MSB = 1 • Vin < Average  MSB = 0 • Bit 3 • (8.125+7.5)/2 = 7.8125 • 7.65 < 7.8125  Bit 3 = 0

  19. Successive Approximation ADC Example • Vin = 7.65 • MSB  LSB • Average high/low limits • Compare to Vin • Vin > Average  MSB = 1 • Vin < Average  MSB = 0 • Bit 2 • (7.8125+7.5)/2 = 7.65625 • 7.65 < 7.65625  Bit 2 = 0

  20. Successive Approximation ADC Example • Vin = 7.65 • MSB  LSB • Average high/low limits • Compare to Vin • Vin > Average  MSB = 1 • Vin < Average  MSB = 0 • Bit 1 • (7.65625+7.5)/2 = 7.578125 • 7.65 > 7.578125  Bit 1 = 1

  21. Successive Approximation ADC Example • Vin = 7.65 • MSB  LSB • Average high/low limits • Compare to Vin • Vin > Average  MSB = 1 • Vin < Average  MSB = 0 • Bit 0 • (7.65625+7.578125)/2 = 7.6171875 • 7.65 > 7.6171875  Bit 0 = 1

  22. Successive Approximation ADC Example • Vin = 7.65 • 110000112 = 19510 • 8-bits, 28 = 256 • Digital Output • 195/256 = 0.76171875 • Analog Input • 7.65/10 = 0.765 • Resolution • (Vmax – Vmin)/2n  10/256 = 0.039 Voltage Bit

  23. ADC Applications e*(∆t) u*(∆t) Controller e e* 0010 1001 0101 1011 0101 0010 1010 0011 • Measurements / Data Acquisition • Control Systems • PLCs (Programmable Logic Controllers) • Sensor integration (Robotics) • Cell Phones • Video Devices • Audio Devices ∆t ∆t t t

  24. ATD10B8C on MC9S12C32 Presented by Quinn Morrison

  25. MC9S12C32Block Diagram ATD 10B8C

  26. ATD10B8C Block Diagram

  27. 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

  28. ATD10B8C Modes and Operations Modes • Stop Mode • All clocks halt; conversion aborts; minimum recovery delay • Wait Mode • Reduced MCU power; can resume • Freeze Mode • Breakpoint for debugging an application Operations • Setting up and Starting the A/D Conversion • Aborting the A/D Conversion • Resets • Interrupts

  29. ATD10B8C External Pins There Are 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

  30. 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

  31. ATD10B8C Control Register 2

  32. ATD10B8C Control Register 3

  33. ATD10B8C Control Register 4

  34. ATD10B8C Control Register 5

  35. ATD10B8C Single Channel Conversions

  36. ATD10B8C Multi-channel Conversions

  37. ATD10B8C Status Register 0

  38. ATD10B8C Status Register 1

  39. ATD10B8C Results Registers

  40. ATD10B8C Results Registers

  41. ATD10B8C ATD Input Enable Register

  42. ATD10B8C Port Data Register

  43. ATD10B8C Setting up the ADC

  44. References • Dr. Ume, http://www.me.gatech.edu/mechatronics_course/ • Maxim Integrated Products, AN1870, AN 1870, APP1870, Appnote1870, Appnote 1870 • "An Introduction to Sigma Delta Converters." Die Homepage Der Familie Beis. 10 June 2008. Web. 27 Sept. 2010. <http://www.beis.de/Elektronik/DeltaSigma/SigmaDelta.html>.

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