ADG751 data sheet has charge injection data ,depend on Source/Drain voltage.
Might be this feature of T-switch type?
Why it has big Qinj when Source/Drain voltage is near VDD?
How about Qinj variation? 20pC or more?
Why it is small at low input voltage?
This feature depend on input or output or both?
Do you have the simulation model?
Could I know the device, more low Qinj T-switch?