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Testing of A/D Converters

Testing of A/D Converters. István Kollár Budapest University of Technology and Economics Dept. of Measurement and Information Systems Budapest, Hungary. Outline. Dynamic measurements: what is the input ? Standards Standardization projects, advantages and problems Main test methods

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Testing of A/D Converters

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  1. Testing of A/D Converters István Kollár Budapest University of Technology and Economics Dept. of Measurement and Information Systems Budapest, Hungary

  2. Outline • Dynamic measurements: what is the input? • Standards • Standardization projects, advantages and problems • Main test methods • Sine wave fit: 3-parameter vs. 4-parameter • 4-parameter fit • Starting values • Algorithm • Programs • LabView • MATLAB • Summary

  3. Input signals • Paradox: determine signal from erroneous data… • Solution: parametric model: • sine wave • exponential • ramp

  4. 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 (in IMEKO TC4)

  5. Location of Code Transitions Direct measurement: feedback loop Histogram – of what? Ramp vs. sine wave Nonlinearity

  6. DFT/FFT Test Test Sine wave Coherent sampling Total harmonic distortion Spurious-free dynamic range Intermodulation distortion

  7. Sine Wave Fitting 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

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

  9. 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)

  10. 3-parameter Fit Linear in A, B, C A, B, C: LS solution of where  is known.

  11. 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

  12. Algorithm I. Minimize vs. , A, B, C

  13. Algorithm II. Algorithm: recursively find LS solution for xi of

  14. Algorithm III. Newton-Raphson method

  15. Algorithm IV. Newton-Gauss method Advantage:

  16. 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

  17. 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

  18. Candidate Programs • MATLAB • LabView • LabWindows • Agilent VEE • GeniDAQ • MATRIXx • Scilab • Mathematica

  19. 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/GeniDAQ%20for%20Windows%20CE.asp MATRIXx, URL: http://www.windriver.com/products/html/matrixx.html Scilab, URL: http://www-rocq.inria.fr/scilab/scilab.html Mathematica, URL: http://www.wolfram.com/

  20. Labview Programs Aim: support IEEE-STD-1057 • Original LabView source • New: stand-alone programs for PC and Macintosh

  21. Labview Program

  22. 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 Matlab is also required

  23. 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

  24. 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

  25. 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)

  26. The Program Page http://www.mit.bme.hu/services/ieee/ADC-test/

  27. The Program

  28. Data Files (Common for Programs) Page: http://www.mit.bme.hu/services/ieee/ADC-test/data/

  29. Summary • The framework • Standard, precise calculations • Flexible interfaces for different purposes • Future work • Version 3.1 is on the internet: http://www.mit.bme.hu/services/ieee/ADC-test/ • Continuous development • Interactive environment • Ideas and comments are appreciated

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