LDO Regulator Zero Compensation With Dual Pass Transistors

Solution Overview

Problem

Conventional low dropout (LDO) regulators face challenges in stability compensation under varying load conditions, particularly when a resistor is used for zero compensation, which can increase chip area and cost due to the need for small resistance values, leading to inaccurate output voltage measurements.

Innovation Solution

The implementation of a control apparatus using two transistors with a resistor and an output capacitor to form a zero, allowing for effective pole compensation without significantly increasing chip area, by configuring the transistors such that the current through the first transistor is N times greater than through the second transistor, and using the resistor and capacitor to set the zero frequency close to the first pole frequency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a resistor is used for zero compensation in conventional LDO regulators, then the stability compensation function is achieved, but the chip area increases and output voltage measurement accuracy decreases

Engineering Contradiction:

Improvestability compensationVSAvoidchip area

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

The patent segments the compensation function by using two transistors (first transistor and second transistor) working in parallel to replace the single large resistor. The first transistor has a larger width-length ratio while the second transistor has a smaller width-length ratio, allowing them to collectively provide the compensation current that would otherwise require a large resistor, thereby reducing chip area while maintaining stability compensation.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent changes the parameters of the transistors (width-length ratio) to optimize their current-carrying capabilities. By configuring the first transistor with a larger width-length ratio and the second transistor with a smaller width-length ratio, the system achieves the desired compensation effect with smaller physical dimensions compared to using a single large resistor.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If a resistor is used for zero compensation in conventional LDO regulators, then the stability compensation function is achieved, but the output voltage measurement accuracy decreases

Engineering Contradiction:

Improvestability compensationVSAvoidoutput voltage measurement accuracy

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The patent segments the compensation function by using two transistors (first transistor and second transistor) working in parallel to replace the single large resistor. The first transistor has a larger width-length ratio while the second transistor has a smaller width-length ratio, allowing them to collectively provide the compensation current that would otherwise require a large resistor, thereby reducing chip area while maintaining stability compensation.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent changes the parameters of the transistors (width-length ratio) to optimize their current-carrying capabilities. By configuring the first transistor with a larger width-length ratio and the second transistor with a smaller width-length ratio, the system achieves the desired compensation effect with smaller physical dimensions compared to using a single large resistor.

Inventive Principle:

Principle #35Parameter changes

3Area of stationary object

If the current through the compensation resistor is reduced, then the chip area is reduced, but the compensation effectiveness may be compromised

Engineering Contradiction:

Improvechip areaVSAvoidcompensation effectiveness

Core Design Contradiction:

Area of stationary objectVSReliability

Solution Approach 1:

The patent segments the compensation function by using two transistors (first transistor and second transistor) working in parallel to replace the single large resistor. The first transistor has a larger width-length ratio while the second transistor has a smaller width-length ratio, allowing them to collectively provide the compensation current that would otherwise require a large resistor, thereby reducing chip area while maintaining stability compensation.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent changes the parameters of the transistors (width-length ratio) to optimize their current-carrying capabilities. By configuring the first transistor with a larger width-length ratio and the second transistor with a smaller width-length ratio, the system achieves the desired compensation effect with smaller physical dimensions compared to using a single large resistor.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS12140986B2Low dropout regulator and control method

Publication Date: 2024.11.12 HALO MICROELECTRONICS INT

AI summary

A low dropout regulator includes a first transistor having a first drain/source terminal coupled to an input terminal of a regulator, and a second drain/source terminal coupled to an output terminal of the regulator, a second transistor having a first drain/source terminal coupled to the input terminal of the regulator, and a second drain/source terminal coupled to the output terminal of the regulator through a resistor, and an error amplifier having an inverting input configured to receive a reference, a non-inverting input configured to detect an output voltage of the regulator, and an output coupled to gates of the first transistor and the second transistor.