Texas Instruments ADS8168EVM-PDK, Руководство пользователя

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ADS8168EVM-PDK Operation
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20 SBAU291 – November 2017
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ADS8168EVM-PDK
6.5 Linearity Analysis Tool
The linearity analysis tool measures and generates the performance DNL and INL plots over code for the
ADS8168. A 2-kHz sinusoidal input signal is required, which is ideally slightly saturated (100–200 mV
outside the full-scale range) with very low distortion. Because the input circuits on the ADS8168 EVM in
their default power configuration do not allow a saturated signal on the negative rail, the linearity algorithm
attempts to report the performance of the codes of the ADC which could be adequately tested. It should
be noted that the results of this test include the nonlinearities of the external signal source, the multiplexer
drive amplifier (if used), and the ADC driver amplifier. For this reason, the external source linearity must
be better than the ADC linearity. To make sure that the DNL and INL of the ADC are correctly measured,
the external source must meet the requirements in
Table 6 .
Table 6. External Source Requirements for ADS8168 Evaluation
Specification Description Specification Value
Signal frequency 2 kHz
External source type Single ended, referred to GND
External source common mode Vref/2, nominally 2.048 V
Signal amplitude Vref/2(Vp) + 100 mVp
Maximum noise 14.5 µV
RMS
Maximum SNR 100 dB
Maximum THD –110 dB
The number-of-hits setting depends on the external noise source. For a 100-dB SNR external source with
approximately 30 µVrms of noise, total number of hits must be 256.
NOTE: This analysis can take a couple of minutes to run and the evaluation board must remain
undisturbed during the complete duration of the analysis.