I have created a differential channel and was testing the channel with simple testbench to check the eye diagram. Now I know the channel performance is very bad (It of several PCB transmission lines, Via & Stubs, and Packaging model). But, I am curious while simulating channel performance, I get negative eye density while checking the eye diagram after the channel which is for me unusual. My channel can be very bad as it is not well matched to 100 ohms. But keep those aside, how can an eye density be negative? what does that mean? If the channel is poor, the can be closed more which I know, but this thing is completely new to me. Can anyone explain why has it happened? I know I can improve it with an improved channel.
Channel S-parameter Plot (Log):