Why my sinewave get distorted when it is 10MHz and above

Question

I am generating an analog sine wave with different frequencies. However, when the frequency is higher than 1MHz, it gets distorted.

This is how 10MHz sinewave looks like

This is the zoomed in version of the same 10MHz sinewave.

This is the FFT of 10MHz sinewave

However, the smaller frequencies does not have this issue.

This is how 1MHz signal looks like

But, when I zoom in, 1MHz signal too has some distortion like this

Also, the Vivado simulation of 10MHz sinewave (16 bit DAC input) looks correct

Following are the steps that I use to generate this waveform

1. I use a custom PCB board with Zynq-7000 (xc7z020clg) FPGA and AD9139 DAC to generate the analog sine wave.
2. I use CORDIC Xilinx IP to generate the 16 bit digital sinewave at 200MSamples/S rate. Then I feed this signal through LVDS pins of AD9139 DAC.

I suspect that this signal is a combination of several harmonics. But I could not figure out why this happens.

I highly appreciate your valuable thoughts on this issue!