Nassek, “Minimizing Gate Capacitances with Transistor Sizing

In this paper a method for choosing appropriate transistor topology for use with transistor sizing is presented. In combinatorial blocks of static CMOS circuits transistor sizing can be applied for delay balancing in order to guarantee synchronously arriving signal slopes at the input of logic gates. Since the delay of a logic gate depends directly on transistor sizes, the variation of channel-widths and-lengths (W and L) allows to equalize different path delays without influencing the total propagation delay of the circuit. Thus, glitching can be avoided. To achieve optimal results, transistor lengths have to be increased, which results in both increased gate capacitances and area. Splitting the long transistors counteracts this negative influence and reduces the power dissipated. A program GliMATS for automated circuit optimization has been implemented. Experimental results show that significant power savings can be achieved with this method. 1