MATLAB Applications of ADC Testing a Tutorial

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MATLAB Applications ofADC Testinga Tutorial

• István Kollár
• Hungary
• Budapest University of Technology and Economics
• Dept. of Measurement and Information Systems

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Outline

• Claim for a standard program
• Standardization projects
• Advantages and problems
• 4-parameter fit
• Starting values
• Algorithm
• Programs
• LabView
• MATLAB
• Summary

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Standardization Projects

• IEEE 1057-1994 (standard for digitizing waveform
  recorders)
• IEEE 1241-2000 (standard for terminology and test
  methods for analog-to-digital converters)
• ? IEC
• DYNAD dynamic characterization and testing of
  analogue to digital converters
• EUPAS European project for ADC-based devices
  standardization

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Focus

• IEEE 1241-2000 (standard for terminology and test
  methods for analog-to-digital converters)
• Sine wave fitting
• Problems detailed description, but
• Complex algorithms using computer
• One-step and/or iterative solutions
• Non-defined or partly defined details
• Not always repeatable results

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Causes of Ambiguity

• Starting values
• Iteration details
• Stop criteria
• Number representation
• Numerical algorithms (roundoff)
• Written standard standard program(s)
• vs. detailed standard

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3-parameter vs. 4-parameter Fit

• 3-parameter
• Frequency ratio must be exactly known
• Linear in the parameters (one-step solution)
• 4-parameter
• More robust
• Works also when the frequency ratio is exactly
  known
• Non-linear in the parameters (iterative solution)

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3-parameter Fit

• Linear in A, B, C
• A, B, C LS solution of
• where ? is known.

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4-p Fit Starting Values

• Nonlinear in ?
• Choice of ? is optional in the standard
• Maximum of DFT (? ??/2)
• Count zero crossings (min. 5 periods)
• Interpolated FFT

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Algorithm I.

• Minimize vs. ?, A, B, C

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Algorithm II.

• Algorithm recursively find LS solution for xi of

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Algorithm III.

• Newton-Raphson method

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Algorithm IV.

• Newton-Gauss method
• Advantage

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Algorithm V.

• Difficulty
• Nothing guarantees decrease of cost function when
  applying step (second-order approximation)
• Stop criterion?
• Good news
• In practice cf almost always decreases,
  especially if at least 5 periods were measured

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Stop Criteria

• Stop if error is small enough (?)
• Largest possible step is already small
• Step below noise level
• Step below noticeable error
• Step below roundoff error
• Display significant bits only

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Candidate Programs

• MATLAB
• LabView
• LabWindows
• Agilent VEE
• GeniDAQ
• MATRIXx
• Scilab
• Mathematica

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Sources of Program Information

• MATLAB, URL http//www.mathworks.com/
• LabView, URL http//www.ni.com/labview/
• LabWindows, URL http//www.ni.com/cvi/
• VEE, URL http//www.get.agilent.com/gpinstruments
  /products/vee/support/
• GeniDAQ, URL http//www.advantech.com/products/Ge
  niDAQ20for20Windows20CE.asp
• MATRIXx, URL http//www.windriver.com/products/ht
  ml/matrixx.html
• Scilab, URL http//www-rocq.inria.fr/scilab/scila
  b.html
• Mathematica, URL http//www.wolfram.com/

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Labview Programs

• Aim support IEEE-STD-1057
• Original LabView source
• New stand-alone programs for PC and Macintosh
• http//grouper.ieee.org/groups/1057/index.html
• Demonstration of program...

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General Requirements for a Program

• Theoretical
• Accurate and fast realization
• Careful documentation of the standard algorithms
• Practical
• Known environment
• User-friendly and flexible interface
• Availability (via internet)
• Interactivity
• LabView is good, but it is not enough

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Why MATLAB?

• Available for several platforms in many labs and
  universities
• IEEE double-precision numbers (64 bit)
• Matrix, vector processing oriented (including
  DFT), implemented in C
• Easy to examine and extend the code
• User-interface support
• Negligible cross-platform compatibility
  problems

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The Framework

• Standard mode
• Curve fitting, DFT and other standardized
  methods, support automatic processing
• Graphical mode
• For visual evaluations
• Compatible mode
• Compatible with the LabView program
• Advanced, development mode
• Test-bed for new ideas

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Interfaces

• User interface
• Graphical user interface
• Self-documentation to support repeatability
• ASCII file format to modify the settings easily
• I/O interface
• Several input file format supporting (ASCII,
  wave, custom)
• Different output files (ASCII, mat, custom)

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The Program - Demonstration

• http//www.mit.bme.hu/services/ieee/ADC-test/

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Data Files (Common for Programs)

• http//www.mit.bme.hu/services/ieee/ADC-test/data/

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Summary

• The framework
• Standard, precise calculations
• Flexible interfaces for different purposes
• Future work
• Version 2.1 is on the internet
  http//www.mit.bme.hu/services/ieee/ADC-test/
• Continuous development
• Interactive environment
• Ideas and comments are appreciated