Please I want to help me to solve the Charge Injection Cancellation I try the dummy transistor is not beneifit. I design a sample and hold phase detector and the O/P was affected by this problem
bottom plate sampling is a technique used to prevent signal dependent charge injection and introduce instead a common mode offset which is removed if working in a differential manner
please refer to any ADC course
Read about it in Johns & Martin or in Razavi (I think). Basically you disconnect the bottom of the sampling cap before disconnecting the input voltage -- then the charge injection is not signal dependent, so it doesn't matter as much for overall linearity, etc...