THE EFFECTS OF CARRIER-VELOCITY SATURATION ON HIGH-CURRENT BJT OUTPUT RESISTANCE

Modern Bipolar Junction Transistors (BJT's) tend to operate with saturated carrier velocity in the collector space-charge region. This paper presents a physical analysis of the effects of velocity saturation on the output resistance of BJT's, especially for high current levels. Physical analyses show that when the collector current density approaches a critical value, the Early voltage can increase significantly due to carrier-velocity saturation as the resulting base push-out partially offsets base-width modulation. This effect is also demonstrated in simulations with PISCES and MMSPICE.