Ac Testing-Fft Capture - Analog Devices EVAL-AD4001FMCZ User Manual

Easy to Use AD4000 Series 16-/18-/20-Bit Precision SAR ADCs User Guide
AC TESTING—FFT CAPTURE
The traditional ac characteristics of the converter can be
displayed on the FFT tab. As in the histogram test, raw data is
captured and passed to the PC where the FFT is performed,
displaying signal-to-noise ratio (SNR), signal-to-noise-and-
distortion ratio (SINAD), total harmonic distortion (THD),
and spurious-free dynamic range (SFDR). The data can also
be displayed in the time domain. To perform an ac test, apply
a sinusoidal signal to the evaluation board at the SMA inputs, J6
and J10. A low distortion, better than 100 dB signal is required
to allow true evaluation of the device. One possibility is to filter the
input signal from the ac source. A band-pass filter can be used,
and its center frequency must match the test frequency of interest.
Furthermore, if using a low frequency band-pass filter when
the full-scale input range is more than a few volts peak-to-peak,
use the on-board amplifiers to amplify the signal, thus preventing
the filter from distorting the input signal.
Figure 23 displays the histogram of the captured data that includes
the following:



Figure 23. FFT Tab (AD4003 Running in Turbo Mode)
Rev. E | Page 13 of 25
The spectrum information.
The fundamental frequency and amplitude in addition to
the second to fifth harmonics.
The performance data (SNR, dynamic range, THD,
SINAD, and noise performance).
UG-1042