Switching Regulator Current Sensing via Differential Amplifier

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Solution Overview

Problem

Conventional switching regulators for microprocessors face challenges in accurately sensing output current due to significant noise introduction, resulting in a low signal-to-noise ratio (SNR), which is undesirable for efficient voltage regulation.

Innovation Solution

A differential current sensing amplifier is used to sense the voltage drop across a main transistor, providing a switched current output to a timing circuit, which in turn generates a timing signal for switching current sample-and-hold circuits to produce a substantially continuous output current, utilizing sensing transistors that replicate the main transistor current with a proportional relationship, thereby improving accuracy and reducing noise.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If conventional current sensing methods are used in switching regulators, then the circuit structure is simple, but the signal-to-noise ratio (SNR) is low due to significant noise introduction

Engineering Contradiction:

Improvesignal-to-noise ratioVSAvoidcircuit structure

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent employs sensing transistors that replicate the main transistor's current characteristics through current mirroring. The sensing transistors are matched to the main transistor and operate in parallel, creating a scaled-down copy of the main current flow. This allows accurate current sensing with high SNR by measuring the replicated current in the sensing transistors rather than directly measuring the large main transistor current, thereby improving measurement precision while maintaining practical circuit complexity

Inventive Principle:

Principle #26Copying

Solution Approach 2:

The current sensing function is segmented into multiple parallel paths: the main transistor carries the full load current, while multiple sensing transistors carry scaled-down proportional currents. The total sensing current is the sum of currents from individual sensing transistors, each contributing a fraction of the main current. This segmentation allows the system to measure current through smaller, lower-noise paths while still representing the total main current accurately

Inventive Principle:

Principle #1Segmentation

2Measurement precision

If conventional current sensing is used, then the circuit is simpler, but the current measurement accuracy is insufficient for efficient voltage regulation

Engineering Contradiction:

Improvecurrent measurement accuracyVSAvoidsensing circuit

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

Inventive Principle:

Principle #26Copying

Solution Approach 2:

The patent implements a feedback mechanism where the summed current from sensing transistors is fed back to the control circuit. This feedback signal represents the main transistor current and is used to regulate the switching regulator's operation. The control circuit adjusts the main transistor's gate voltage based on this feedback to maintain desired output voltage and current levels, ensuring accurate and efficient voltage regulation

Inventive Principle:

Principle #23Feedback

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This approach enhances the signal-to-noise ratio (SNR) of current sensing, enabling more accurate and efficient real-time current monitoring and adaptive voltage regulation in low voltage high current microprocessor applications, improving measurement accuracy by up to one order of magnitude.

Implementation Method 1

a differential current sensing amplifier adapted for sensing a voltage drop across a main transistor

Methodology Applied

Scientific EffectVoltage drop sensing: Ohm's Law

Implementation Method 2

one or more sensing transistors, each sensing transistor being adapted for producing a sensing inductor current, wherein the sensing inductor current is smaller than and related to the main transistor current

Methodology Applied

Scientific EffectCurrent replication through transistor matching:

Implementation Method 3

the timing circuit which is adapted for providing a timing signal to one or more switching current sample-and-hold circuits based on a current waveform of the switched current output

Methodology Applied

Scientific EffectWaveform-based timing:

Implementation Method 4

the one or more switching current sample-and-hold circuits, each of which are adapted for producing a substantially continuous output current

Methodology Applied

Scientific EffectSample-and-hold circuit operation:

Data Source

PatentUS9817039B2Methods for sensing current in a switching regulator

Publication Date: 2017.11.14 MONOLITHIC POWER SYSTEMS INC

AI summary

In one embodiment, a current sensing circuit includes a differential current sensing amplifier adapted for sensing a voltage drop across a main transistor, the differential current sensing amplifier being adapted for providing a switched current output to a timing circuit which is adapted for providing a timing signal to one or more switching current sample-and-hold circuits based on a current waveform of the switched current output, and the one or more switching current sample-and-hold circuits, each of which are adapted for producing a substantially continuous output current. In another embodiment, a method for detecting a current includes driving a main transistor with a first current, driving one or more sensing transistors with a second current, measuring a sensing inductor current of the one or more sensing transistors, and determining the first current based on the sensing inductor current, wherein the sensing inductor current is related to the first current.