FFT Metrics

RF Data Converter Interface User Guide (UG1309)

Document ID
UG1309
Release Date
2021-10-27
Revision
1.4 English

There are many converter metrics on the RF-ADC FFT page. These metrics are listed and defined as follows.

Figure 1. RF-ADC FFT Metrics
dBFS
dBFS is the full scale of the RF-ADC expressed in dB, normalized to 0. The corresponding dBm value of 0dBFS depends on the ADC's input full scale range, which is listed in the Zynq UltraScale+ RFSoC Data Sheet: DC and AC Switching Characteristics (DS926).
FundA
RMS power level of fund signal expressed in dBFS.
SFDR
Spurious-free dynamic range (SFDR) expressed in dBc. SFDR is the ratio of the RMS value of the signal to the RMS value of the peak spurious spectral component for the analog input that produces the worst result.
SFDRxH23
SFDR excludes the second and third harmonic distortion in dBc. The location of harmonic distortions are predictable and hence can be handled separately in application. Therefore, a separate SFDRxH23 is listed for reference.
Fspur
The frequency location of the worst spur in MHz in the first Nyquist band.
FspurxH23
The frequency location of the worst spur excludes the second and third harmonic distortion in MHz in the first Nyquist band. This specification still includes ADC OIS, GTIS, and PLL reference spurs.
THD
Total harmonic distortion (THD) in dBc. THD is the ratio of the RMS signal energy to the RMS value of the sum of the first six harmonics.
NSD
Noise spectrum density (NSD) in dBFS/Hz. NSD is the RMS noise power per Hz normalized to full scale in the first Nyquist band. The noise power in this software indicates total other power except the power of the found signal.
SNR
Signal to noise ratio (SNR) in dB. SNR is the ratio of the RMS signal amplitude to the RMS value of the sum of all the spectral components except the first six harmonics and dc. The unit in dBFS indicates the signal here and refers to full scale of RF-ADC.
SNDR
Signal to noise and distortion ratio (SNDR) expressed in dBc. SNDR is the ratio of the RMS signal amplitude to the RMS value of the sum of all spectral components except fund signal. It is similar to SNR, but includes all the harmonics.
IM3
Third-order inter-modulation (IM3) distortion products expressed in dBc. IM3 used in dual-tone testing, indicates the ratio of RMS signal amplitude to the maximum RMS amplitude of 2F2 ± F1 or 2F1 ± F2 .
Fref Spurs
Spurs generated by the input reference (the frequency of phase-frequency-detector) of the PLL, including its harmonics. When using an external PLL for clocking the Zynq UltraScale+ RFSoC directly, you must indicate the reference frequency in the PLL tab for this evaluation tool GUI to calculate the Fref spurs. The RF-ADC is built with interleaving technology. Spurs of offset interleaving and gain/timing interleaving are listed on the RF-ADC FFT tab by choosing Interleaving Performances.
Interleave Offset
The frequency location and amplitude of offset interleaving spurs.
Interleave Gain
The frequency location and amplitude of gain/timing interleaving spurs.