The influences of ICs' no-connection pins on noise immunity

Experimental results that the existence of no-connection pins (open pins) of integrated circuits (ICs) degrades noise immunity and influences the oscillation phenomena occurring near threshold level are described. To evaluate the susceptibility of the ICs with open pins, the ratio of the output voltage of ICs with pins clamped through a series resistor to a power supply (no open pins) to the output voltage of ICs with open pins is proposed as an index, in the case that pulsive noise is applied to input line assigned to signal input. The influence of the open pins and these pins clamped through resistors to power supply on the noise immunity is quantitatively clarified. The cause of noise immunity degradation due to the existence of open pins and the cause of weakness of the clamping effect are detailed. The optimum method for clamping open pins is proposed.<>