Part Number: LMX2595
Hello TI Support (Noel Fung),
We are using LMX2595 in a broadband synthesizer design with 1 kHz steps.
Below are four traces, showing significant changes in performance depending on the setting of PFD_DLY. We would like to understand what is happening.
In Trace1, Fo = 8,001,600KHz, we see very large spurious spaced roughly 490Khz apart.
In Trace2, Fo = 8,001,601KHz (1KHz offset), the spurs are gone but the noise floor is increased dramatically. We think this may be the same spurious but spread/integrated into the spectrum (but not well).
In Traces 1 and 2 below PFD=2, which should satisfy the Minimum N requirement in 7.3.4 Table 2.
Trace 1
Trace 2
In Trace 3 and 4 below we changed PFD=1, and both the spurious and noise are reduced quite a bit.
Trace 3
Trace 4
- Could you please provide some explanation of what we are seeing?
- Could you also please provide a more detailed explanation in Table 2, of the function PFD_DLY and mash order. These parameters have a dramatic effect on spectral performance and it’s not clear to us how to set them in a broadband frequency application.
Regards,
Richard Scheer