Semicustom Design of Zigzag Power-Gated Circuits in Standard Cell Elements

Zigzag power gating (ZPG) can overcome the long wake-up delay of standard power gating, but its requirement for both nMOS and pMOS current switches, in a zigzag pattern, requires complicated power networks, limiting application to custom designs. We propose a design framework for cell-based semicustom design of ZPG circuits, using a new power network architecture that allows the unmodified conventional logic cells to be combined with custom circuitry such as ZPG flip-flops, input forcing circuits, and current switches. The design flow, from register transfer level description to layout, is described and applied to a 32-b microprocessor design using a 1.2-V 65-nm triple-well bulk CMOS process. The use of a sleep vector in ZPG requires additional switching power when entering standby mode and returning to active mode. The switching power should be minimized so that is does not outweigh the leakage saved by employing ZPG scheme. We formulate the selection of a sleep vector as a multiobjective optimization problem, minimizing both the transition energy and the total wirelength of a design. We solve the problem by employing multiobjective genetic-based algorithm. Experimental results show an average saving of 39% in transition energy and 8% in total wirelength for several benchmark circuits in 65-nm technology.