How can we help without seeing your design?
We don´t see your simulation, too.
And we don´t see how much your ENOB drops.. maybe it´s just 0.01dB, maybe it is 20dB?
We don´t see the frequency range of your input sine wave.
We don´t see the amplitude of your input sine wave.
Give us informations, so that we have at least a chance to help.
You will have issues with the front end S/H amplifier
tracking a faster-slewing signal. You could quantify
the error at the hold node / A-D comparator front
end.