Demystifying Switched Capacitor Circuits

Basic MOS Device Physics

11

thereby having no effect on the output voltage (V

out

). As clk falls, a channel is formed

under the dummy’s gate despite the shorted drain and source. Ideally, the charge

injected by the full-size main switch would be canceled out by the intrinsic channel

charge (with a polarity opposite to that of the former) induced by the half-size

dummy. However, in reality, the size ratio of “1/2” rarely works out to be the

optimum required for achieving the perfect charge injection cancellation, due to

circuit imperfections such as the fi nite clock slope and body effect [2][9]. In fact, the

optimization of the size ratio is a rather ...