Laboratory 4: Measuring a 10 Bit C2C DAC

Components:


1 x Breadboard
22 x Capacitors (10 pF, 100 pF, 1 nF)
Amplifier and sample and hold:
1 x LF398
1 x LM324
1 x ALD1106
1 x ALD1107
2 x Resistors 100 kΩ
Easy wiring:
5 x 12 Pin connectors

Task:


Measure static and dynamic performance of a DA-converter.
Experience measurement problems and learn how to improve INL and DNL by circuit adjustments and digital assistance.
This is an open laboratory.

Build a 10-Bit C2C DAC according to the circuit below using only the operational amplifier LM324, not yet the sample and hold LF398 and connect it with the Electronic Explorer:


Operational amplifier LM324:
 Sample and hold LF398:

Make a photo of your setup connected to the electronic explorer.

Measurement equipment:


For measurements the Electronic Explorer board is used:

Operation of Electronic Explorers

Measuring performance of the measurement equipment:


Connect AWG 1 with SCOPE OSC1 DC to estimate the INL, DNL and signal to noise of the waveform generator and the oscilloscope.
Start the oscilloscope and the arbitrary waveform generator.
Select a sine signal with a frequency of 53.71749481 kHz an amplitude of 2 V and an offset of 2 V.
For channel 1 select a time range of 2 µs per division, range of 500 mV/div and offset of -2 V.
Creat a math function generating positive integer values: round(C1 * 2* 1024 + 200).
Check with the vertical minimum function of M1 that all values are positive.
Export the values and copy them to the clipboard.
Copy the integer values into the input field of the FFT, INL, DNL tool:
FFT_Javascript_2017_Calibration.html
Do 'Read positive integer data'.
Set the number of points to 8192 and the number of bits to 12.
Do 'Generate Charts'.
Check the input signal for number of periods and range.
What is the signal to noise, INL and DNL value.
What is the maximum number of bits, which can be measured?
Discuss your results, document your challenges and results.
Make screenshots of the FFT analysis.

Ramp and sine measurement of the DAC:


Generate a binary counter pattern with the pattern generator and look with the oscilloscope at the output of the 10-bit DAC.


  1. Measure the capacitance value of each capacitance with a multi meter.

    Name C1 C2 C3 C4 C5 C6 C7 C8 C9 C10 C11 C12
    C [pF]
    Name C13 C14 C15 C16 C17 C18 C19 C20 C21 C22 C23 C24
    C [pF]
    Name C25 C26 C27 C28 C29 C30 C31
    C [pF]

  2. What is the offset, maximum voltage and LSB of the DAC?
    Open the 'Patterns' window.
    Create a bus with D[0]..D[9].
    Use the type binary counter, output PP.
    Select a frequency of 10 MHz, 1 MHz, 100 kHz, 10 kHz under 'parameter' for the counter.
    Connect the MSB to OSC 2 DC as a trigger signal.
    Connect the output of the DAC to OSC3 DC and change the counter frequency until you have a sawtooth curve.
    Make sure that the settling time of the signal is ok for a full level transition.
    Use the full vertical range of the oscilloscope to minimize error.
    Channel 1 should show the output voltage, channel 2 and 3 should show D9 and D0.
    Document challenges, effort and results and discuss your results.

  3. Measure and extract INL and DNL using ReadOsci.html

    Details:
    With the oscilloscope do export data.
    Copy the data into the 'input data' field.
    Make sure to measure a positive ramp.
    Set 'DNL, INL start', 'DNL, INL averaging length', 'DNL, INL step' and 'DNL, INL number of values' to appropriate values.
    Set option for measurement analysis to 'Ramp INL, DNL'.
    Do 'Process oscilloscope data'.
    Document and discuss the result.
    Select a frequency of 10 MHz, 1 MHz, 100 kHz, 10 kHz under 'parameter' for the counter.
    What is the best frequency for the pattern generator for operation?
    Document challenges, effort and results and discuss your results.

  4. Select the best frequency from the previous task. Can you improve the INL and DNL of the transfer characteristic by changing capacitors?
    Measure the improved circuit.
    Document the improved capacitance values.
    Document challenges, effort and results and discuss your results.

  5. Use a digital sine input and measure signal to noise ratio using a fft.
    Import 10Bit_Sine43Periods.csv into the pattern generator of the Electronic Explorer.
    Import 10Bit_Sine1Period.csv into the pattern generator of the Electronic Explorer.
    You can use DDS_Sim_Javascript_2016.html to generate other digital sine signals.
    Measure with different frequencies.
    Document challenges, effort and results and discuss your results.

  6. Use DDS_Sim_Javascript_2016.html to calculate a calibration lookup table and generate a better ramp and sine signal.

    Step by Step:

    1) Start with DDS Javascript and fill 0..511 into Calibration and do (7) generate 1024 vectors with calibration for EE
    2) Save the generated vectors on the drive and import them into the digital pattern generator:
    type custom, edit parameters, Import file, open file, browse ok import
    3) Measure the ramp with the oscilloscope and export the data
    4) Do ReadOsci.html
    and do 'Digital calibrated INL, DNL'
    The calibration data appear at the bottom
    5) Copy the calibration data into the DDS Javascript Calibration data and generate 1024 vectors.
    6) Use this vectors for the pattern generator.
    7) Look at the oscilloscope data with Read osci and the reduced number of codes and look for INL and DNL
    8) Use a sine waveform with calibration data and without, and compare SNR


    Can you improve the INL and DNL of the transfer ramp characteristic by using digital calibration?
    Can you improve the INL, DNL and signal to noise ratio of the sine characteristic by using digital calibration?
    Measure the improved circuit.
    Document challenges, effort and results and discuss your results.

  7. Document your results.

Report


Make a report as a web page. You can use the source code of this web page or there is a web page template available here.
Additional files are here as an zip file (39 MB).

Send a ziped group directory with your data containing also a printout of the webpage in a pdf file to joerg.vollrath@fh-kempten.de.

You can use the freeware program PDF Creator for generating the pdf file.

The directory should be named with the year, group number and last name

<year>_Group<###>_<Last_name>
Example: 2017_Group01_Vollrath

In this directory put the html and pdf file.
The file name should contain the date, the laboratory and your last names.

<year>_<month>_<Date>_InEl_Lab02_<Last_name1>_<Last_Name2>.pdf
Example: 2017_10_24_InEl_Lab04_Vollrath_studentx.html
Example: 2017_10_24_InEl_Lab04_Vollrath_studentx.pdf



Grading:

Each question should be answered. The answer should be correct/make sense. The submission date will be graded. Submission should happen until 22.1.2018. Late submission will be downgraded. A nice document format and correct use of English language and spelling is graded.