Charge-Borrowing Decap: A Novel Circuit for Removal of Local Supply Noise Violations

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Executive Summary

The authors propose a novel circuit called Charge-Borrowing Decap (CBD) as a drop-in replacement for passive decaps to reduce supply noise for removal of "Hot-spot" IR-drop problems found late in the design process. Measurement results on a 90nm test chip show that a noise reduction improvement between 42%-55% at 100MHz-1.5GHz over its passive counterpart. The increase in clock frequency and on-chip current demand makes power grid design a challenging task. Decoupling capacitors (decaps) are generally used to reduce IR drop and Ldi/dt effects, and hence keep the power supply relatively constant. Starting from 90nm, simply placing passive decaps in the available open areas of the chip may not be sufficient.

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