Power Gate Replica Bias Control for Stable Digital Voltage Regulation
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Solution Overview
Problem
Digital voltage regulators face challenges in maintaining loop stability, transistor reliability, and self-heat issues due to unbounded transient current steps and process variations, particularly in measuring power gate current accurately for on-die voltage regulation.
Innovation Solution
A power gate replica circuit is used to measure and regulate current, comparing it against a reference current and adjusting the gate bias, which simplifies the control loop and reduces self-heat by limiting current per branch, thereby improving stability and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If power gate devices are digitally switched from OFF to fully ON, then the voltage regulator can provide on-die linear voltage regulation, but unbounded fast transient current steps occur that can collapse the input power delivery network
Solution Approach 1:
The patent applies dynamic current limiting by implementing a control mechanism that adjusts the power gate current based on real-time conditions. The system dynamically limits the rate of current change (di/dt) during transient events, preventing unbounded current steps while maintaining fast response capability. This is achieved through a control loop that monitors and regulates the power gate current, transforming the static switching behavior into a dynamic, controlled process that eliminates harmful transients while preserving productivity.
2Ease of operation
If power gate devices are switched to fully ON, then voltage regulation is provided, but transistor reliability decreases and self-heat issues occur at high dropout voltage
Solution Approach 1:
The patent implements preliminary anti-action by proactively limiting the current through power gate devices before excessive self-heat and reliability degradation can occur. The control mechanism pre-establishes current limits that prevent the devices from operating in harmful high-power regions. By anticipating and preventing the conditions that lead to self-heat issues and reliability problems, the system maintains voltage regulation capability while protecting transistor reliability through preventive current management.
3Measurement precision
If voltage drop across power gate is measured to infer current, then current sensing is achieved, but measurement accuracy is limited due to process and voltage variations and small voltage drop signals
Solution Approach 1:
The patent employs copying by creating a replica of the power gate device with identical characteristics. This replica power gate is used to sense the current by measuring the voltage drop across it, which is then used to control the actual power gate. The copying approach eliminates the need for direct measurement of the main power gate, providing accurate current sensing through the replica while maintaining process and voltage variation immunity. This method achieves high measurement precision without significantly increasing device complexity.
4Adaptability or versatility
If current sensing is performed with process variations, then power management features are affected, but accuracy and repeatability deteriorate with steep tradeoffs between power, speed, and accuracy
Solution Approach 1:
The patent implements self-service by using the power gate replica to automatically sense and report its own current through voltage drop measurement. The replica device inherently provides the sensing function without requiring external sensing circuits or complex measurement systems. This self-sensing mechanism maintains accuracy and repeatability across process variations because the replica experiences the same process conditions as the main power gate. The system achieves adaptability in power management while maintaining measurement precision through this self-service approach.
Data Source
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AI summary
A reduced-size replica of power gate transistors may be used within a closed-loop voltage regulator to measure the average current delivered by the transistors in the non-replica power gate. The measured current is compared against a known reference current, and a feedback loop is used to modify the gate bias of the power gate and replica power gate transistors. An improved current sensing power gate replica solution may include measuring current from a small replica of the power gate and extrapolating the total current by digitally multiplying the replica current by the ratio of the size of the enabled power gates to the size of the replicas. The current through the replicas, which substantially matches the current in equivalent power gate devices, may be collected on an analog bus and conducted across a known resistor to generate a voltage that determines an estimated current of the power gate devices.