Soft-Start Power Gating With Voltage Detection for Secondary Rails
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Solution Overview
Problem
Conventional methods for charging secondary voltage rails in integrated circuits (ICs) lead to inefficient current draw from the main power rail, resulting in noise and potential electromigration violations, and lack feedback control to optimize charging based on the secondary voltage rail's charge state.
Innovation Solution
A power gating circuit with automatic voltage level detectors and main power gate switches that selectively charge the secondary voltage rail based on detected voltage levels and initial power control indicators, using a soft start process to minimize initial current draw and switch on the main power gate only when the secondary rail reaches a predetermined voltage level.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional switches are used to charge the secondary voltage rail, then the secondary voltage rail can be powered up, but excessive current draw and noise are generated on the main power rail
Solution Approach 1:
The patent applies preliminary action by first charging the secondary voltage rail to a preliminary voltage level before enabling full power. The circuit selectively charges the secondary voltage rail to a preliminary voltage level prior to enabling a voltage island, which prevents excessive current draw and noise on the main power rail while still achieving the necessary power-up state.
2Speed
If the main power gate is switched on immediately, then fast power-up is achieved, but electromigration violations and noise occur on the main power rail
Solution Approach 1:
The patent performs preliminary charging of the secondary voltage rail to a preliminary voltage level before activating the main power gate. This staged approach enables faster power-up compared to conventional methods while avoiding electromigration violations and noise by preventing sudden full-power activation.
Solution Approach 2:
The patent implements dynamic control of the power gating process by adjusting the charging stages based on the voltage level detected. The circuit dynamically transitions from preliminary charging to full power activation, optimizing both speed and reliability by adapting the power-up sequence to actual circuit conditions.
3Device complexity
If conventional open-loop control is used, then the circuit is simple, but the charging process cannot be optimized based on the secondary voltage rail's charge state
Solution Approach 1:
The patent implements feedback control by detecting the voltage level on the secondary voltage rail and using this information to control the power gating process. The voltage level detector provides feedback to determine when to transition from preliminary charging to full power activation, optimizing charging efficiency while maintaining relatively simple circuit complexity.
Data Source
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AI summary
A method and apparatus for selectively charging a secondary voltage rail includes selectively and partially charging a secondary voltage rail using at least one soft start power gate switch and using an initial power control indicator. The partially charged secondary voltage rail is selectively charged, using at least one main power gate switch, based on the initial power control indicator and a detected voltage on the secondary voltage rail. When the initial power control indicator is in a state representative of an initial power up command and when the detected voltage is greater than or equal to a predetermined voltage level, at least one main power gate switch is closed thereby charging the secondary voltage rail.