Chopped Current Sensing Circuitry for Low Offset and Flicker Noise

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Solution Overview

Problem

Current sensing techniques in electronic systems face challenges in achieving high accuracy, low noise, and low offset drift, particularly in high-side current sensing applications, where existing methods often introduce noise and offset issues due to temperature drift and flicker noise from current sources.

Innovation Solution

The proposed current sensing circuitry employs a differential amplifier with a switch network that alternates between two chopping configurations at different frequencies, along with level-shifting current sources and a current source chopper, to modulate and cancel out noise and offset, utilizing a low-pass filter to remove modulated offset and flicker noise, thereby reducing noise effects and improving accuracy.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If conventional current sensing techniques are used, then current measurement capability is achieved, but noise and offset drift increase due to temperature variations and flicker noise from current sources

Engineering Contradiction:

Improvecurrent measurement accuracyVSAvoidnoise and offset drift

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent applies periodic chopping action to modulate the current sources at a specific frequency. The current sources are switched between connected and disconnected states periodically, which modulates the offset and noise components to higher frequencies where they can be filtered out by the low-pass filter, thereby improving measurement precision while reducing the harmful effects of offset drift and flicker noise.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The patent converts the harmful offset and flicker noise from current sources into a beneficial signal by modulating them at a chopping frequency. The low-pass filter then removes these modulated components, effectively transforming the harmful noise and offset into a filterable signal that can be eliminated, thus improving current measurement accuracy.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

2Ease of operation

If current sources are used for level shifting in differential amplifier, then biasing is achieved, but temperature drift and flicker noise are introduced

Engineering Contradiction:

Improveamplifier biasingVSAvoidtemperature drift

Core Design Contradiction:

Ease of operationVSTemperature

Solution Approach 1:

The patent employs periodic chopping of the current sources at a defined frequency. This periodic modulation causes the temperature drift and flicker noise components to appear at the chopping frequency and its harmonics, which are then rejected by the low-pass filter, allowing the amplifier to maintain proper biasing while minimizing temperature drift effects.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The patent introduces a chopping signal as an intermediary mechanism that mediates between the current sources and the amplifier inputs. This chopping action transforms the direct DC offset and temperature drift into AC components at the chopping frequency, which can be easily separated and filtered from the measurement signal.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Measurement precision

If high sensitivity and high accuracy current sensing is implemented, then measurement capability is improved, but the circuit becomes more susceptible to offset and noise from current sources

Engineering Contradiction:

Improvesensing accuracyVSAvoidoffset and noise from current sources

Core Design Contradiction:

Measurement precisionVSObject-generated harmful factors

Solution Approach 1:

The patent uses periodic chopping of the current sources to modulate the offset and noise to higher frequencies. The low-pass filter then removes these modulated harmful components while preserving the measurement signal, thereby maintaining high sensing accuracy while reducing the impact of offset and noise generated by the current sources.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The patent converts the harmful offset and noise from current sources into a beneficial modulated signal that can be easily filtered. By chopping the current sources at a specific frequency, the offset and noise are transformed into AC components that stand out from the DC measurement signal, allowing for effective separation and removal through filtering.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Data Source

PatentUS11835554B2Current sensing circuitry

Publication Date: 2023.12.05 CIRRUS LOGIC INC

AI summary

The present application relates to current sensing circuitry (100) that comprises a differential amplifier (110) comprising first and second inputs configured to sense a current across a sense resistance, and an output configured to output a current sense signal. The circuitry (100) further comprises a first current source, a second current source and a switch network operable in: a first phase in which the first current source is connected to the first input and disconnected from the output, and the second current source is connected to the output and disconnected from the first input; and a second phase in which the first current source is connected to the output and disconnected from the first input, and the second current source is connected to the first input and disconnected from the output.