Reducing dynamic errors of integrated-circuit CMOS switches

Analog CMOS switches and commutators such as those of series 590 and 571 feature high open-state resistance, low and nonlinear conducting-state resistance, low residual voltage, bidirectionality, potential coupling between switch or commutator circuit and control circuit, high speed, and voltage as well as current switching capability. Their major drawbacks are high interference level and long transient period, high input and output capacitances, high temperature coefficient of resistance and appreciable open-circuit leakage current. An analysis of an inverter-controlled CMOS transistor pair reveals that interference signals generated by passage of the control-voltage pulsefront through the gate-channel capacitances in the two complementary transistors, successively, do not compensate one another but add up. At the same time, the main cause of a slow output signal transient are transients in the control circuit which prolong the rise time of the control-voltage pulse. The oscillatory transient with overshoots travels through the gates to the channels, subsequently appearing across the switch resistance and thus prolonging the output signal transient.