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# How to measure DAC DNL & INL?

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#### spbhu

##### Member level 2
how to measure dnl

Dear all,
I have a 13 bit DAC, with the sampling rate (1Mb/s), I know normally people will measure the SINDR, which will be used to calculate the ENOB, and hence estimate the DNL & INL, how can I directly obtain the DNL & INL values? Could anybody suggest the ways and the required instruments I need to use? Thanks a lot.

how to measure dnl of dac?

inl in dac depends on mismatch so you can simulate
it, whatever the inl is the difference between the output signal and the required output

how to calculate dnl in a dac?

I guess you are asking for testing the DAC chip on board.

there are several posts available in this forum regarding the testing of ADC/DAC. You can go through them. The first hand material will be the Handbook of Data Converters by Walt Kester (from ADI). This book is available in this board as well as in ADI site (free). This is having a dedicated chapter on testing.

There are several methods of doing the test you asked for (INL/DNL). A common practise is to use a slow ramp at input (the digital input data to DAC will be like 00--00, 00--01,--11--11). Now you will get the analog equivalent at the DAC output. You have to measure the analog signal (either by high accuracy voltmeter or any other good instrument that won't through error more than the DAC). Now you will be having a mapping curve. This is the characteris tics of the DAC. You now can easily calculate DNL/INL from this. To avoid the later part (the high accuracy voltmeter to measure ther analog output of the DAC), people also use an easier method. They connect an ADC (having at leat 2/3 bit more true resolution than the DAC) at the DAC output. Now you will have the ADC output Vs. the dig. data input. Here from you can calculate the same. As DNL/INL is static characteristics, I guess, frequency of operation won't affect the measured result.

sankudey

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