Posted by Godwin Maben on August 21, 2009
Hearing many concerns on topics related to power gated design and its relation to decoupling capacitor to reduce IR-Drop issues. Thought of writing a paragraph on this topic.
Power gated designs requires addition of decoupling capacitor to power network to resolve dynamic IR-drop issues. Decoupling cap insertion becomes more challenging in the power-gated designs compared to normal designs. Besides the issues of high leakage power in the de-caps , de-caps added to the virtual power network has significant impact on the wakeup latency and in-rush current. Larger the decoupling capacitance, Larger the in-rush charge current and longer time to wakeup. On the other hand, de-caps, inserted in the permanent power network, does not affect the wakeup latency and in-rush current. Therefore, optimization of de-cap insertion in the power-gating design should not only minimize total capacitance of the de-caps but we should also consider adding some capacitance to the virtual power network while meeting the dynamic IR-drop target.
- Godwin Maben