Design and Technology Co-optimization Utilizing Multi-bit Flip-flop Cells

Abstract

The benefit of multi-bit flip-flop (MBFF) as opposed to single-bit flip-flop is sharing in-cell clock inverters among the master and slave latches in the internal flip-flops of MBFF. Theoretically, the more flip-flops an MBFF has, the more power saving it can achieve. However, in practice, physically increasing the size of MBFF to accommodate many flip-flops imposes two new challenging problems in physical design: (1) non-flexible MBFF cell flipping for multiple D-to-Q signals and (2) unbalanced or wasted use of MBFF footprint space. In this work, we solve the two problems in a way to enhance routability and timing at the placement and routing stages. Precisely, for problem 1, we make the non-flexible MBFF cell flip-ping to be fully flexible by generating MBFF layouts supporting diverse D-to-Q flow directions in the detailed placement to improve routability and for problem 2, we enhance the setup and clock-to-Q delay on timing critical flip-flops in MBFF through gate upsizing (i.e., transistor folding) by using the unused space in MBFF to im-prove timing slack at the post-routing stage. Through experiments with benchmark circuits, it is shown that our proposed design and technology co-optimization (DTCO) flow using MBFFs that solves problems 1 and 2 is very promising.