Power Delivery

Substrate Power Integrity

At BroadPak, power integrity is an integral part of the co-design process. In fact, during the co-design process IR drop modeling and analysis is a routine task and is well integrated into the substrate design flow.

BroadPak flow not only predicts an accurate voltage profile but also shows where the power integrity problems may exist so the silicon design team can rectify them before tapeout. Power delivery design and structure has first order effect on:

-- Simultaneously Switching Noise Output (SSO/SSN)
-- Core voltage stability
-- Silicon architecture, bump (pin out) topology
-- Substrate design

IR drop is a well known cause of chip failure at lower process nodes. As the process node shrinks to 14nm and beyond, power rail integrity issues are observed at the silicon level and in the field for two chief reasons:

1- Deep-submicron designs require low power supply voltages, this reduces the chip's threshold to noise (noise margin)

2- Deep-submicron designs results in many more transistors per die. More transistors consume more power this will strain the chip's power delivery network resulting in Dynamic Voltage Drop.

The importance of power integrity analysis at smaller process nodes can't be emphasized more; conductor resistance, inductance effects and capacitive parasitics results in IR drop. Subsequently, IR drop causes delay and slew rate changes that leads to set-up and hold-time violations. Set-up violation in turn results in slow chip performance and hold-time violation results in more severe chip failure.

Low threshold for noise margin makes the chip vulnerable to glitches and failure. Decoupling caps used to ease the IR drop if not used wisely are also a cause of increased power leakage.

It is important to realize that voltage drop not only varies across the chip but also in time across the clock cycle as a function of mode. Thus the factors that stress the power delivery network must be included in the analysis.

At high speed, determining the frequency at which the cavity formed between the power and ground plane resonate is the key to a successful power delivery management. These resonances are the major cause of SSO noise and cross-talk.