PLL Voltage Boosting for Frequency Overshoot Mitigation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Phase locked loops (PLLs) experience frequency overshoot when correcting phase or frequency changes, leading to increased supply voltage guard bands, which negatively impact system performance and limit the effectiveness of adaptive frequency scaling techniques.
Innovation Solution
An apparatus that temporarily boosts the supply voltage before a potential frequency overshoot event, allowing the PLL to lock quickly without long-term voltage guard bands, and then reduces the voltage back to its expected level, thereby avoiding unnecessary increases in minimum operating voltage (Vmin).
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the supply voltage is increased to compensate for frequency overshoot, then the PLL can maintain stable operation, but the minimum operating voltage (Vmin) increases and system performance decreases
Solution Approach 1:
The patent applies preliminary action by boosting the supply voltage to the PLL in advance before a frequency overshoot event occurs. This proactive voltage increase prepares the PLL to quickly acquire or re-acquire lock without experiencing significant frequency overshoot, thereby maintaining stable operation without requiring a permanently elevated Vmin that would degrade system performance.
2Loss of time
If the PLL lock time is reduced for faster frequency transitions, then adaptive frequency scaling effectiveness improves, but frequency overshoot increases
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the supply voltage parameter of the PLL based on operational conditions. When fast frequency transitions are required, the voltage is temporarily increased to enable quicker lock acquisition. This dynamic parameter adjustment allows the system to achieve fast lock times without incurring harmful frequency overshoot, as the voltage is optimized for each specific transition event rather than maintained at a fixed high level.
3Reliability
If supply voltage guard bands are increased to absorb frequency overshoot, then the compute subsystem can operate reliably, but the extent to which adaptive frequency scaling can be used is limited
Solution Approach 1:
The patent applies preliminary action by proactively boosting the supply voltage before frequency overshoot events occur, rather than relying on static guard bands. This approach allows the compute subsystem to operate reliably at lower Vmin levels because the voltage compensation is applied dynamically and temporarily only when needed, preserving the ability to use aggressive adaptive frequency scaling techniques across a wider range of operating conditions.
Data Source
AI summary
An apparatus and method are described, which prior to an event that could result in frequency overshoot, sends a signal to a voltage regulator or generator requesting a temporary supply voltage and/or current boost. This enables a clocking source, such as a phase locked loop (PLL) to lock fast while not needing any long-term voltage guard bands. The apparatus and scheme allows for on-the-fly change in supply voltage and/or clock frequency for a processor with little to no impact on Vmin. During the clock frequency overshoot, the supply voltage is temporarily boosted and then reduced down to the expected voltage level of the power supply. Such boost allows for absorbing the clock frequency overshoot impact. The supply voltage level can be reduced in a step-wise fashion to avoid any potential undershoot in clock frequency.