I  studied materials about bottom plate sampling by Prof. Song and found something interesting. Here is the first figure about bottom plate sampling. I am looking forward any materials about the figure in the 2nd post . I also found a figure looks pretty much like the one in the 2nd post. I tried to post the 1st and 2nd figures in one post but can not make it. Sorry for any inconvenience I made.

I don't know what your problem is.

Ron needs to be small enough to satisfy the settling/linearity requirements. You can do hand calculations to get an idea.

Regards

Berti wrote on Aug 28^th, 2009, 5:05am:


The settling would be determined by the total Ron, but I think he is looking for the optimal relative sizes of the two switches.

I hadn't seriously analyzed it, but I would think you would want the top switch resistance to be as small as possible (i.e. make it a wide switch). This is because its resistance is signal dependent so you want to minimize its effect. In addition, charge injection effects are minimized because the bottom switch is open so there is little penalty to a large switch.

On the other hand, the bottom switch contributes to the charge injection. Most is common mode and signal independent, but some isn't. You would want to minimize its effects by making the switch as small as possible... that is, you would want the bottom switch resistance to dominate the settling time.

I'm just rattling this off the top of my head, but the above seems to make sense. It doesn't seem to be consistent with the plot. Ideas?

rg

Neglecting linearity and just considering area, the switches should be sizes the same dimensions.

Cheers