Sundance SMT391 - Manual (Page 10)

Version 1.5 Page 10 of 18 SMT391 User Manual
Performances
Introduction
The following figures show data captures using the SMT391-VP to capture the data
and MATLAB to plot and display it. As the SMT391-VP is a broadband converter no
type of band-pass filtering were used when capturing these results. FFT Spurs might
thus seem high at certain points, but in a specific system application selective signal
filtering will significantly increase the quality of the captured signal. The analogue
input signal used is also not derived from the same clock source as the sampling
clock. There is thus also no frequency coherence, which will once again add
additional spurs to the FFT.
VCO Clock
The following figures show captures of the performance of the SMT391 onboard
VCO clock. This data was measured at the point where this clock is distributed to the
FPGA. The 1000MHz clock is split, one side goes to the ADC, and the other side is
divided by 8 (giving a 125MHz clock) and then passed on to the FPGA.
Figure 4 – FFT of Div 8 Version of 1000MHz System Clock.