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ME6405 DAC Lecture

10/23/2003. ME6405 - DAC Lecture. 2. Overview. What is a DAC?General Characteristics of DACsTypes of DACsBinary Weighted ResistorR/2R LadderCommon Errors in DACsApplications. 10/23/2003. ME6405 - DAC Lecture. 3. Digital to Analog Converter. What is a digital to analog converter (DAC)?Converts

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ME6405 DAC Lecture

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    1. 10/23/2003 ME6405 - DAC Lecture 1 ME6405 DAC Lecture Sunij Chacko Pierre Emmanuel Deliou Thomas Holst

    2. 10/23/2003 ME6405 - DAC Lecture 2 Overview What is a DAC? General Characteristics of DACs Types of DACs Binary Weighted Resistor R/2R Ladder Common Errors in DACs Applications

    3. 10/23/2003 ME6405 - DAC Lecture 3 Digital to Analog Converter What is a digital to analog converter (DAC)? Converts digital input signal to an analog output signal

    4. 10/23/2003 ME6405 - DAC Lecture 4 Digital to Analog Converter

    5. 10/23/2003 ME6405 - DAC Lecture 5 What a DAC Looks Like:

    6. 10/23/2003 ME6405 - DAC Lecture 6 General DAC Characteristics Resolution Linearity Speed Settling Time Reference Voltages

    7. 10/23/2003 ME6405 - DAC Lecture 7 Resolution The variation of the output voltage corresponding to the variation of the least significant binary bit (LSB) Inversely proportional to the number of bits Commonly 12-bit because of tradeoff between cost and resolution

    8. 10/23/2003 ME6405 - DAC Lecture 8 Linearity

    9. 10/23/2003 ME6405 - DAC Lecture 9 Speed Rate of conversion of a single digital signal to its analog equivalent Depends on: Clock speed of input signal Settling time of DAC

    10. 10/23/2003 ME6405 - DAC Lecture 10 Settling Time

    11. 10/23/2003 ME6405 - DAC Lecture 11 Reference Voltages Non multiplier DAC: Vref is fixed—given by the Manufacturer Multiplier DAC: Vref can be variable Multiplies digital word by analog Vref input

    12. 10/23/2003 ME6405 - DAC Lecture 12 Full Scale Voltage Full scale voltage is determined using the reference voltage

    13. 10/23/2003 ME6405 - DAC Lecture 13 Types of DAC 2. Two types of DAC Binary Weighted Resistor DAC R-2R Ladder DAC

    14. 10/23/2003 ME6405 - DAC Lecture 14 Binary Weighted Resistor DAC

    15. 10/23/2003 ME6405 - DAC Lecture 15 Binary Weighted Resistor DAC Analysis

    16. 10/23/2003 ME6405 - DAC Lecture 16 Binary Weighted Resistor DAC Analysis

    17. 10/23/2003 ME6405 - DAC Lecture 17 Binary Weighted Resistor DAC The output will be:

    18. 10/23/2003 ME6405 - DAC Lecture 18 Binary Weighted Resistor DAC Example:

    19. 10/23/2003 ME6405 - DAC Lecture 19 Binary Weighted Resistor DAC Advantage Easy principle (low bit DACs) Disadvantages Requirement of several different precise input resistor values: one unique value per binary input bit. (High bit DACs) Larger resistors ~ more error. Precise large resistors – expensive. High number of bits lead to current changes in the magnitude of noise amplitudes.

    20. 10/23/2003 ME6405 - DAC Lecture 20 R-2R Ladder DAC

    21. 10/23/2003 ME6405 - DAC Lecture 21 R-2R Ladder DAC Analysis

    22. 10/23/2003 ME6405 - DAC Lecture 22 R-2R Ladder DAC Analysis

    23. 10/23/2003 ME6405 - DAC Lecture 23 R-2R Ladder DAC Analysis

    24. 10/23/2003 ME6405 - DAC Lecture 24 R-2R Ladder DAC Analysis

    25. 10/23/2003 ME6405 - DAC Lecture 25 R-2R Ladder DAC Analysis The output will be:

    26. 10/23/2003 ME6405 - DAC Lecture 26 R-2R Ladder DAC Only two resistor values- R and 2R Does not need the kind of precision as Binary weighted DACs Easy to manufacture More popular Less errors

    27. 10/23/2003 ME6405 - DAC Lecture 27 Common DAC Errors 3. DAC Errors Gain Error Offset Error Non-Linearities Monotony

    28. 10/23/2003 ME6405 - DAC Lecture 28 Gain Error Distance between the theoretical value and the real value measured on the last transition of the converter and expressed in LSB. Assumes the adjustment of the zero is completed.

    29. 10/23/2003 ME6405 - DAC Lecture 29 Offset Error Distance between the theoretical value and the real value measured on the first transition of the converter and expressed in LSB

    30. 10/23/2003 ME6405 - DAC Lecture 30 Linearity The linearity error of is due to the fact that the resolution of the converter is not constant Two types: Integral non linearity Differential non linearity

    31. 10/23/2003 ME6405 - DAC Lecture 31 Integral non-linearity It is the maximum difference noticed on all the range of conversion between the theoretical values and the real values

    32. 10/23/2003 ME6405 - DAC Lecture 32 Differential non linearity It is the difference of tension obtained during the passage in the next digital code.

    33. 10/23/2003 ME6405 - DAC Lecture 33 Monotony Inflection in the transfer function For one Output value, two binary input are possible.

    34. 10/23/2003 ME6405 - DAC Lecture 34 Overall Precision It’s the sum of all previous errors. It’s given in a percentage of the full scale.

    35. 10/23/2003 ME6405 - DAC Lecture 35 Applications Conventional use Programmable gain OpAmps Programmable Filters Multiplier

    36. 10/23/2003 ME6405 - DAC Lecture 36 Conventional use Used at the end of a digital processing chain when an analog signal is required. It will be followed by a filter in order to abolish the ‘steps’ inherent to the digitalization.

    37. 10/23/2003 ME6405 - DAC Lecture 37 Programmable gain OpAmps Voltage controlled Amplifier (digital input, Vref as control) Digitally operated attenuators (Vref as input, digital control)

    38. 10/23/2003 ME6405 - DAC Lecture 38 Programmable Filters Integrate DACs in filters Variable cutoff frequency commended by a digital signal

    39. 10/23/2003 ME6405 - DAC Lecture 39 References http://www.allaboutcircuits.com http://www.dwelle.de/rtc/infotheque/digital_signal/conversion.pdf http://hyperphysics.phy-astr.gsu.edu http://www.fujitsu.com

    40. 10/23/2003 ME6405 - DAC Lecture 40 Acknowledgements Dr. I. Charles Ume Teaching Assistants Students from previous years.

    41. 10/23/2003 ME6405 - DAC Lecture 41 Questions?

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