A method of shortening metastable operation duration time by the use of feedback

If metastable operation (MS operation) occurs in conflict-resolving circuits, propagation delay time of flip-flop (FF) increases by the amount of its duration time and a malfunction may occur. This paper proposes a method of shortening duration time of MS operation that occurs when two inputs of RSFF consisting of CMOS NAND gates are switched from logic 0 to 1 approximately at the same instant. The MS operation is detected and fed back to inputs so that it is forced to terminate. A configuration of RSFF that has feedback based on this idea is first presented, and then a principle of shortening MS operation duration time follows. Then, considering implementation of RSFF by n-well process, feedback connection and MOSFET parameters are optimized. Although hardware increases slightly by addition of feedback, the result shows the MS operation duration time increase rate against input phase difference (switching time difference of two inputs of RSFF), and the range of input phase difference for MS operation incidence are reduced by approximately 1/4 and 1/3, respectively, compared with conventional methods.