Gated clock routing for low-power microprocessor design

This paper presents a zero-skew gated clock routing technique for VLSI circuits. Gated clock trees include masking gates at the internal nodes of the clock tree, which are selectively turned on and off by the gate control signals during the active and idle times of the circuit modules to reduce the switched capacitance of the clock tree. We construct a clock tree topology based on the locations and the activation frequencies of the modules, while the locations of the internal nodes of the clock tree (and hence the masking gates) are determined using a dynamic programming approach followed by a gate reduction heuristic. This work assumes that the gates are turned on/off by a centralized controller. Therefore, the additional power and routing area incurred by the controller and the gate control signal routing are examined. Various tradeoffs between power and area for different design options and module activities are discussed and detailed experimental results are presented. Finally, good design practices for implementing the gated clocks are suggested.