Figure 6-6. Spectral Analysis Tool - Texas Instruments ADS131B26Q1EVM-PDK User Manual

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6.3.2 Spectral Analysis Tool
The Spectral Analysis tool is intended to evaluate the dynamic performance of ADC1A, ADC3A, ADC1B, and
ADC3B. This tool analyzes the AC characteristics of the ADC and input signal source.
The Data Capture Configuration panel on the left side of the window allows the user to independently specify the
oversampling ratio (OSR) used by ADC1A, ADC3A and ADC1B, ADC3B by configuring OSR13A and OSR13B,
respectively. Even though the resulting data rates can differ, the resulting fast-fourier transform (FFT) always
plots from DC to one-half the data rate for each channel. Therefore, one channel FFT plot can easily occupy less
of the x-axis than the other.
The Measurements summary table above the FFT plot is updated based on the Display Channel drop-down
menu selection. The calculated specifications include SNR, THD, SFDR, SINAD, and ENOB. The GUI also
identifies the frequency and signal power of the fundamental component of the input signal, and the frequency
and signal power of the largest spur component.
Under the Configuration section, select the number of harmonics used for distortion calculations (default = 9
harmonics) and specify the windowing function required to mitigate the effects of non-coherent sampling. The
7-Term Blackman-Harris window is the default option and has sufficient dynamic range to resolve the frequency
components of a 24-bit ADC. The None option corresponds to not using a window (or using a rectangular
window) and is not recommended. Both the calculated specifications and the FFT plot can be displayed in dBc
or dBFS units by toggling the radio buttons beneath the Display Channel drop-down menu.
Figure 6-6 shows the Spectral Analysis Tool window. Initiate a data capture by specifying the number of samples
and clicking the Capture button at the bottom of the Data Capture Configuration panel. In the example below,
ADC3A is configured for 64 kSPS (OSR13A = 64) and is measuring a 2-kHz single-ended sine wave, producing
a –6.26 dBFS input signal. The resulting FFT is plotted from DC to 32 kHz. For fully-differential inputs, restrict
the input signal amplitude to –0.5 dBFS maximum (approximately 95% of full-scale) to avoid saturating the ADC
channels and introducing unwanted distortion terms into the signal. ADC3B is configured to measure an internal
short to AGNDB at 32 kSPS (OSR13B = 128). As a result, the noise floor of ADC13B is only plotted from DC to
16 kHz.
SBAU413 – OCTOBER 2022
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Figure 6-6. Spectral Analysis Tool

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ADS131B26Q1EVM-PDK Software Reference
ADS131B26Q1EVM-PDK Evaluation Module 21