Switching with MOSFETs. With the addition of the capacitors here, these are "sample and hold" or "track and hold" circuits.
Note how the single-NMOS switch doesn't turn on fully when the input is more than about half the "on" gate voltage, and fails to turn off when the input is more negative than the "off" voltage.
The two-FET switch always turns on fully, but fails to turn off when the input exceeds either gate voltage.
