Efficient power pad assignment for multi‐voltage SoC and its application in floorplanning

Abstract

Multi-voltage techniques are being developed to improve power savings by providing lower supply voltages for noncritical blocks under the performance constraint. However, the resulted lower voltage drop noise margin brings serious obstacles in power/ground (P/G) network design of the wire-bonding package. For voltage drop optimization, both block and power pad positions are important factors that need to be considered. Traditional multi-voltage floorplanning methods use rough estimation to evaluate the P/G network resource without considering the locations of power pads. To remedy this deficiency, in this paper, an efficient voltage drops aware power pad assignment (PPA) method is proposed, and it is further integrated into a floorplanning algorithm. We first present a fast PPA method for each power domain by the spring model. Then, to evaluate voltage drops during floorplanning iterations, the weighted distance from the blocks to the power pads is adopted as an optimization objective instead of time-consuming matrix computation. Experimental results on Gigascale System Research Center (GSRC) benchmark circuits indicate that the proposed method generates an optimized placement of power pads and floorplanning of blocks with high efficiency.decoupling capacitors configuration to alleviate the power delivery noise [12,13]. However, those techniques are implemented only when the floorplan or placement is ready. With exploding design complexity, it is necessary to consider voltage drop issues in the early design cycle [14][15][16][17]. Once the voltage drops aware floorplan is obtained, the detailed P/G network design can be performed in the subsequent placement and routing stages that consider Steiner tree construction and electromigration issues [18,19].It is reported that 5% of voltage decrease may cause the circuit performance slowdown up to 15% or more [20]. Hence, designers typically limit the voltage drops within 10% of the supply voltage to guarantee faultless operation [21]. Lower supply voltage indicates that lower noise margins or smaller voltage drops are permitted on the P/G network [22]. For instance, 1.5-V supply voltages permit 150-mV voltage drop while 1.0-V supply voltages only allow 100-mV voltage drop. Compared with single-voltage SoC, the voltage drop constraints present more challenges for the P/G network design of the multi-voltage SoC. First, from a low-power perspective, a VI with a larger area and a lower supply voltage is preferred during the VI generation process. However, the permitted ultra-low voltage drops make the P/G network hard to design. Second, power pads are located at the periphery of the chip for wire-bonding package. Locations of power pads affect both the timing and voltage drops [23]. Although multiple power pads for each VI can leverage the voltage drops, it may not be practical because the power pads must compete with other signal I/Os under the limited pad resource. Thus, it is vital to consider voltage drops in P/G network design for multi-voltage SoC. Related workConsid...

Power aware floorplanning in multiple supply voltage domain

“…A group of works have considered the technique post floorplanning stage, whereas some have considered it during floorplanning stage. Ching et al, Wu et al, and Lee et al [1][2][3] have concentrated on post-floorplanning stage, whereas Chu et al, Lin and Hung, and Zhou et al [4][5][6][7][8] have considered them in floorplanning stage. Voltage island-driven floorplanning can be further classified into two groups.…”

“…Voltage island-driven floorplanning can be further classified into two groups. The first group [9][10][11] considers regions of voltage island to be scattered, whereas latter group 4,5,12 considers the locations to be contiguous.…”

“…13 have put forward a two phase method to deal with partitioning of blocks based on consideration of signal nets and power domain. After distribution module shapes and locations of each domain are determined, Chu et al 5 have proposed a voltage drop aware power pad assignment technique where each power domain is represented by a spring model. The technique optimizes weighted distance between power pad and block.…”