Bulk Current Regulation for LDO Dropout Reduction
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Solution Overview
Problem
Low-dropout (LDO) regulators face challenges in achieving smaller device size without compromising performance or efficiency, particularly in minimizing dropout voltage and quiescent current while maintaining high output current capabilities.
Innovation Solution
The implementation of a bulk-current regulation technique that senses and controls the bulk current of the output transistor based on its source-drain current, maintaining an operating value within an active range and reducing it outside this range to optimize transistor performance and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If the output transistor size is reduced to decrease device area, then device size is reduced, but dropout voltage increases and performance deteriorates
Solution Approach 1:
The patent dynamically changes the bulk voltage parameter of the output transistor to optimize its performance. By adjusting the bulk voltage based on the operating current range, the transistor maintains better performance characteristics with a smaller size, resolving the contradiction between device area and dropout performance.
Solution Approach 2:
The bulk voltage is made dynamic rather than fixed, adapting to different operating conditions. The circuit automatically adjusts the bulk voltage according to the current range, enabling the transistor to operate optimally across different load conditions while maintaining a compact size.
2Reliability
If the threshold voltage is reduced to decrease dropout voltage, then dropout voltage is reduced, but leakage current increases and efficiency deteriorates
Solution Approach 1:
Instead of changing the threshold voltage, the patent changes the bulk voltage parameter to reduce dropout voltage. This approach avoids increasing leakage current while still achieving better voltage regulation, as the bulk voltage modulation affects the transistor's effective threshold and channel characteristics without the same leakage penalties.
Solution Approach 2:
The bulk voltage acts as an intermediary parameter that indirectly controls the transistor's effective threshold voltage and channel conductivity. By modulating the bulk voltage, the patent achieves dropout voltage reduction without directly altering the gate threshold voltage, thereby avoiding the leakage current increase that would result from threshold voltage reduction.
3Reliability
If the bulk current is increased to improve transistor performance, then dropout voltage is reduced, but quiescent current increases and efficiency deteriorates
Solution Approach 1:
The bulk current is made dynamic and adaptive, varying with the operating conditions rather than being constant. The circuit increases bulk current only when needed (in the active current range) to improve transistor performance, and reduces it during low-current operation to minimize quiescent current consumption, thus resolving the efficiency contradiction.
Solution Approach 2:
The patent applies bulk current modulation only partially - specifically within the active current range where it provides benefit. The adaptive circuit determines when bulk current adjustment is necessary and applies it only in those conditions, avoiding excessive bulk current that would increase quiescent power consumption during low-load operation.
Data Source
AI summary
An illustrative method embodiment includes: sensing a source-drain current provided by the output transistor; and controlling a bulk current from a body terminal of the output transistor in response to the source-drain current. The controlling includes: maintaining the bulk current at an operating value while the source-drain current is in an active range; and reducing the bulk current below the operating value when the source-drain current lies outside the active range. An illustrative circuit embodiment includes: an output transistor that supplies an output current over a range that includes an active region; and a bulk current adapter that senses the output current and responsively controls a bulk current from a body terminal of the output transistor, maintaining the bulk current at an operating value while the output current is in the active region and reducing the bulk current when the output current is outside the active region.