Tool/software:
hi,
We used the lmx2820 to generate 7G to 16G clocks and had some issues. Here are the related schematics and layout.
The output clock is connected to the load (ADC) via a short track and two separate capacitors. (highlighted part)
The input clock is 122.88MHz/245.76MHz, the output 15,728.64MHz and 14,745.6MHz are normal, but when the after the double VCO is turned off (output of 7,864.32MHz and 7,372.8MHz), the clock quality is very poor. Use an oscilloscope to measure the signal on the capacitor, and the results are as follows.
It can be seen that the output of the two frequencies is accompanied by a large number of harmonic components, mainly the second and third harmonics.
We have tried to modify the capacitor or remove the capacitor directly with 100Ω resistor short connection, and also tried to modify the register of LMX2820 and the filter circuit of CPOUT to VTUNE. The results are not significant, so I would like to ask you if there is a better solution.
Thanks.
