LDO Pass Device Recovery via Current Boost Circuit
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Solution Overview
Problem
Low dropout (LDO) regulators face inefficiencies due to slow recovery of pass transistors from triode to saturation regions, leading to delayed voltage regulation and increased power consumption, which affects the performance of RF power amplifiers in burst mode operations.
Innovation Solution
A circuital arrangement with a current boost circuit that mirrors the output stage of an operational amplifier, providing a current boost during transitions of pass devices between saturation and triode regions based on detected control voltage ramping, thereby reducing capacitive loading and enhancing current drive capability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the pass device is driven into its triode region of operation to minimize power loss, then power consumption is reduced, but the LDO operates in open loop mode where the output voltage is not regulated and recovery time from saturation is delayed
Solution Approach 1:
The circuit applies a preliminary voltage boost to the gate of the pass device before the normal control voltage can charge the gate capacitance. This preliminary action accelerates the transition from triode to saturation region, reducing recovery delay while maintaining the ability to drive the device into triode for power savings during steady-state operation
Solution Approach 2:
The circuit uses a detector that periodically monitors the control voltage and triggers a current boost when transitioning from triode to saturation region. This periodic intervention provides fast recovery only when needed (during transitions) while allowing the device to remain in power-saving triode mode during steady-state regulation
2Speed
If the operational amplifier drives the pass device quickly back into saturation region, then voltage regulation recovery is faster, but power consumption of the operational amplifier increases
Solution Approach 1:
The operational amplifier includes a preliminary current boost stage that activates only during transition periods when the pass device needs to recover from triode to saturation region. This preliminary action provides high current only when needed for fast recovery, rather than continuously, thereby reducing overall power consumption while maintaining fast recovery speed
Solution Approach 2:
The current boost circuit is triggered periodically by a detector that monitors the control voltage ramping. The boost current is applied only during the brief transition period when recovery is needed, and is disabled during steady-state operation, thus achieving fast recovery speed only when necessary while minimizing operational amplifier power consumption
Data Source
AI summary
Systems, methods and apparatuses for efficient control of a pass device driven into its triode region of operation are described. Output drive capability of an operational amplifier driving the pass device is boosted during a transition of the pass device from operating in a triode region to operating in a saturation region. An exemplary implementation of an LDO controlling pass devices for providing burst RF power to a power amplifier is described. An alternative configuration that boosts the driving capability of the operational amplifier using an asymmetrical mirroring circuit is also described.