Texas Instruments ADS1285EVM-PDK, User Manual, Page: 20 / 40

8.5 Histogram Tool
Noise degrades ADC resolution and the histogram tool can be used to estimate effective resolution, which is an
indicator of the number of bits of ADC resolution losses resulting from noise generated by the various sources
connected to the ADC when measuring a DC signal. The cumulative effect of noise coupling to the ADC output
from sources such as the input drive circuits, the reference drive circuit, the ADC power supply, and the ADC
is reflected in the standard deviation of the ADC output code histogram that is obtained by performing multiple
conversions of a DC input applied to a given channel.
As shown in Figure 8-5 , the histogram corresponding to a DC input is displayed on clicking the Capture button.
Figure 8-5. Histogram Analysis Tool
8.6 DAC Configuration Tool
The DAC configuration tool page ( Figure 8-6 ) controls the onboard DAC1282, a test DAC specifically designed
to work with the ADS128x family of devices. As previously discussed in Section 6 , the DAC output frequency is
programmable from 0.5 Hz to 250 Hz and the magnitude is scaled by both analog and digital control. The analog
gain is adjustable in 6-dB steps and the digital gain in 0.5-dB steps. The analog gain settings match those of the
ADS1282 for testing at all gains with high resolution. More information about each setting can be found in the
DAC1282 data sheet.
In general, the most important outcomes of changing the DAC are to understand the mode, output amplitude,
and output frequency (if applicable). In the middle, the
Operation box shows the Mode drop-down, which can be:
Sine, DC, digital pulse, and pulse.
For Sine, the amplitude is determined by a combination of the analog gain and digital gain settings. In addition,
the DAC page uses the Vref (V) drop-down menu to calculate the values in the gray boxes, although the DAC
does not need to know the reference voltage to function. As a result, review the Sine AMP (Vp) calculation,
in combination with the ADC gain on the register map page, to understand the output code and voltage of the
ADC. The frequency is determined by typing a desired frequency into the
Desired Frequency (Hz) text box. The
GUI automatically displays the closest Freq, M, and N values to achieve the desired output frequency that are
ADS1285EVM-PDK Software Reference www.ti.com
20 ADS1285EVM-PDK Evaluation Module SBAU394A – APRIL 2022 – REVISED SEPTEMBER 2022
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