Apparatus for increasing the speed of a circuit having a string of IGFETs

摘要

In an IGFET circuit having a long string of more than two transistors connected in series between an output terminal and a power supply terminal where the load capacitance across the output terminal is on the same order of magnitude as the parasitic capacitances at the junctures of the transistors in the string, the switching-delay is not significantly reduced by uniformly increasing the conduction channel widths of the transistors in the string. However, according to the present invention, a substantial reduction in the switching delay of such a circuit may be obtained by scaling the conduction channel widths of the transistors in the string so as to provide a positive gradient in conduction channel widths along the string in the direction from the output terminal to the power supply terminal. It is particularly advantageous to use exponential scaling of the conduction channel widths. The present invention is also applicable to transistor strings which include one or more groups of parallel connected transistors.