Pre-charged LDO with Cutoff Transistor for Fast Wake-up
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Solution Overview
Problem
Conventional low-dropout regulators (LDOs) in wireless devices require complex sleep bias circuits to prevent transistor breakdown, leading to increased complexity, size, and cost, and slow wake-up times from sleep mode due to the need for charge time periods.
Innovation Solution
The design incorporates a cutoff transistor and a current source to enable the LDO to enter sleep mode without a separate sleep circuit, allowing for fast wake-up and maintaining a non-breakdown voltage across transistors, eliminating the need for complex sleep bias circuitry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional LDOs use complex sleep bias circuits to prevent transistor breakdown, then reliability is improved, but device complexity increases
Solution Approach 1:
The patent extracts and eliminates the separate sleep bias circuit from the LDO design. Instead of using a complex dedicated sleep bias circuit to prevent transistor breakdown, the invention uses a simple cutoff transistor controlled by a sleep signal to disconnect the output, thereby preventing breakdown without requiring complex biasing circuitry during sleep mode.
Solution Approach 2:
The patent introduces a cutoff transistor as an intermediary element between the LDO output and the load. This cutoff transistor acts as a mediator that can quickly disconnect the output during sleep mode, preventing transistor breakdown without requiring complex sleep bias circuits. The cutoff transistor is controlled by a sleep signal and provides a simple yet effective solution to the reliability-complexity contradiction.
2Reliability
If conventional LDOs use complex sleep bias circuits, then transistor breakdown is prevented, but the LDO wake-up time increases due to charge time requirements
Solution Approach 1:
The patent removes the charge time requirement by eliminating the complex sleep bias circuit. The simple cutoff transistor approach allows instantaneous disconnection during sleep mode and rapid reconnection upon wake-up, eliminating the gradual charging process required by conventional sleep bias circuits and thereby reducing wake-up time significantly.
Solution Approach 2:
The patent enables the LDO to skip the gradual charge-up process by using a cutoff transistor that can instantly disconnect and reconnect the output. When transitioning from sleep to active mode, the cutoff transistor can be rapidly turned on, allowing the LDO to rush through the wake-up process without waiting for capacitor charging, thus dramatically reducing wake-up time while still preventing transistor breakdown.
3Reliability
If conventional LDOs include complex sleep bias circuitry, then transistor protection is achieved, but the overall size and cost of the LDO increase
Solution Approach 1:
The patent extracts and removes the complex sleep bias circuitry from the LDO design, replacing it with a simple cutoff transistor and control logic. This extraction eliminates unnecessary components, reduces circuit size, and lowers manufacturing cost while maintaining the essential function of preventing transistor breakdown during sleep mode.
Solution Approach 2:
The patent employs a simple, inexpensive cutoff transistor instead of complex, expensive sleep bias circuitry. The cutoff transistor is a basic, readily available component that provides the necessary protection function at minimal cost, making the overall LDO design more cost-effective and compact while achieving the same reliability goals.
Data Source
AI summary
Embodiments described herein present a new LDO design that eliminates the need for the sleep bias circuitry included in other systems. Further, the new LDO design can be biased with a small fraction of the operating current enabling the LDO to wake up substantially faster than previous LDO designs that include separate sleep circuitry. In some cases, the LDO can instantly (or faster than other LDOs) transition from a sleep mode to an operating mode enabling improved operation compared to prior LDOs. Furthermore, the new LDO design maintains a non-breakdown voltage across the transistors reducing the need to enter sleep mode to prevent transistors of the LDO from entering a breakdown region.