Evaluation of time resolution of NMOS sampling switches

Usually in CMOS line receivers and downconversion mixers, a key component is the NMOS sampling switch. When designing sampling switches, one has usually to trade off resolution against bandwidth and aperture time. In this perspective, we modeled the aperture time of the NMOS sampling switch for low swing voltage signals taking also into account the dependence of the threshold voltage on the body effect. Then we compared the aperture time behaviour using three submicron CMOS technologies (0.8, 0.5 and 0.25 μm minimum channel length respectively). The results indicate that an aperture time of about 100 ps is achievable with a CMOS 0.25 μm minimum channel length technology working at low supply voltage.