Virtual-Tile-Based Flip-Flop Alignment Methodology for Clock Network Power Optimization
Clock network plays the most significant role in power consumption in IC design. Since a clock network normally has a high switching ratio, power optimization of the clock network is one of the best solutions to minimize dynamic power and total power in modern IC designs. The clock network is synthesized based on an initial flip-flop placement. The number of clock buffers and their sizes are decided by the initial placement. Moreover, clock wires, which are the major sources of clock power consumption, are also constructed based on the flipflop placement. As a result, the flip-flop placement determines the quality of the clock network. In this article, we propose a new clock network optimization method to reduce the dynamic power consumption of clock network. The method first creates virtual tiles over the entire design area and selects the most effective columns to align flip-flops in lines. Once the effective columns are determined, flip-flops are relocated based on the virtual tiles in the columns considering the minimum moving distance. By aligning flip-flops, it is possible to significantly reduce both wire capacitance and wire length. Since it does not change the clock structure, unlike the conventional clock network optimization techniques which use multibit flip-flop or register bank, there is no degradation in timing or other constraints. Experimental results show that the proposed method reduces the wire capacitance, wire length, and via count up to 23.2%, 10.2%, and 16.4%, respectively, in five industrial intellectual property (IP) designs. The reduction in clock network power is 14.1% on average.
Cell placement, clock network optimization, clock tree synthesis (CTS), flip-flop alignment, flip-flop relocation, multibit flip-flop (MBFF).