Transistor chaining in CMOS leaf cells of planar topology

A technique for chaining the transistors in the layouts of static CMOS leaf cells is presented and analyzed. This new method is superior to existing techniques, since it can operate on a more general class of circuits and is very efficient. It is shown that the layout width of a CMOS leaf cell can be significantly reduced (nearly 40% in the average case) by transistor chaining. Moreover, more than half of the switching functions of four variables have optimal CMOS circuit implementations with nonseries/parallel topologies. Therefore, the use of nonseries/parallel circuits can have a positive global impact on layout area and performance. The transistor chaining technique presented in this paper produces the optimal solution for 82% of the circuits tested, and has linear time complexity.