Mixed-Stack Digital Voltage Regulator for Dropout Reliability
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Solution Overview
Problem
Conventional voltage regulators face reliability issues due to high dropout voltage and load current variations, leading to excessive power dissipation and potential instability, especially when operating with high dropout voltage and low load current conditions.
Innovation Solution
A digital voltage regulator with a mixed-stack power stage comprising parallel combinations of single, double, and triple transistor stacks, controlled by a control unit to maintain output voltage within a target range using a combination of thermometer and binary codes, and bias voltages to equalize transistor resistance across different stack heights.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a small number of power transistors are placed in conducting states to handle high dropout voltage and low load current, then the voltage regulator can operate under high dropout conditions, but the current draw per conducting transistor becomes relatively high leading to excessive power dissipation
Solution Approach 1:
The power transistor is divided into multiple segments (first plurality and second plurality of transistors) that can be independently controlled. This segmentation allows the regulator to distribute current across multiple smaller transistor units rather than overloading a single transistor, thereby reducing power dissipation per transistor while maintaining the ability to handle high dropout voltage conditions.
Solution Approach 2:
The system dynamically adjusts the number of conducting transistors based on operating conditions. The control unit selectively activates transistors from the first plurality during high dropout/low current conditions and transistors from the second plurality during low dropout/high current conditions, optimizing the balance between reliability and power dissipation in real-time.
2Loss of energy
If the control unit selectively activates different transistor groups based on operating conditions, then power dissipation is reduced under high dropout conditions, but the device complexity increases
Solution Approach 1:
The control unit monitors and responds to changes in operating parameters (dropout voltage and load current levels) by selectively activating different transistor groups. This parameter-based control strategy allows the system to adapt to varying conditions without requiring complex control logic, as the activation decisions are based on straightforward threshold comparisons of voltage and current levels.
3Reliability
If multiple transistor stacks with different numbers of series-connected transistors are used, then current density distribution is improved, but the manufacturing precision requirements increase
Solution Approach 1:
Different transistor stacks are designed with different numbers of series-connected transistors (first stack with first number, second stack with second number) to create local variations in current handling capacity. This local quality differentiation allows each stack to be optimized for specific current density requirements, improving overall current distribution while the control unit manages the complexity of coordinating these diverse stacks.
Data Source
AI summary
Some embodiments include an apparatus including a first node in a voltage regulator, a second node in the voltage regulator, and a power stage to receive a first voltage from the first node and provide a second voltage at the second node. The power stage includes a first circuit path and a second circuit path coupled in parallel with each other between the first and second nodes. The first circuit path includes a first number of at least one transistor coupled between the first and second nodes. The second circuit path includes a second number of at least one transistor between the first and second nodes. Wherein the first number is unequal to the second number.