1kV from Simple Op Amp Circuit?

Hi,
I am getting familiar with ADS and created what I thought was a simple comparator. I fed in a 1V 1kHz signal compared to ground.
I expected the output to saturate and get an output that looked like a squarewave. Instead, I get a 1kV sinewave output. I'm not sure why the output exceeds its rail voltages, since it appears that it should max out at 0.3V below the rail voltage.

What am I missing here?

Thanks

附图/附件

1kV_Circuit.JPG

1kV_Graph.JPG

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