LDO Regulator Buffer Circuit Pole Shifting
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The presence of a buffer circuit in low dropout voltage regulators introduces an additional pole in the Bode diagram, which can degrade system stability and reduce closed-loop bandwidth due to its proximity to the output pole.
Innovation Solution
A buffer circuit structure is implemented with a follower amplifier and a negative feedback amplifier in a common gate configuration, along with a transistor active load, to shift the additional pole to higher frequencies, improving stability and increasing bandwidth by reducing impedance and increasing the frequency of the additional pole.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a buffer circuit comprising a follower amplifier is inserted between the output node of the error amplifier and the gate of the output transistor, then the capacitance on the output node of the error amplifier is decreased and the charging/discharging time of the gate is reduced, but an additional pole is introduced in the Bode diagram which degrades system stability
Solution Approach 1:
The patent introduces a second amplifier stage as an intermediary component between the follower amplifier and the output transistor gate. This additional intermediary shifts the location of the pole introduced by the buffer circuit to a higher frequency, moving it away from the output pole and thereby resolving the stability issue while preserving the fast charging/discharging capability.
2Speed
If a buffer circuit is inserted to decrease output node capacitance, then the reaction speed is improved, but the closed-loop bandwidth is reduced due to the additional pole
Solution Approach 1:
The second amplifier stage acts as an additional intermediary that modifies the frequency response characteristics of the buffer circuit. By inserting this stage, the pole frequency is shifted higher, which prevents the bandwidth reduction that would otherwise occur due to the interaction between the buffer circuit's pole and the output pole.
Data Source
AI summary
The regulator with low dropout voltage comprises an error amplifier and an output stage comprising an output transistor and a buffer circuit comprising an input connected to the output node of the error amplifier, an output connected to the output transistor, a follower amplifier connected between the input and the output of the buffer circuit. The buffer circuit furthermore comprises a transistor active load connected to the output of the follower amplifier and a negative feedback amplifier arranged in common gate configuration and connected between the output of the follower amplifier and the gate of the transistor of the active load.