Continuous-Time Chopper Instrumentation Amplifier With Minimal Aliasing

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Solution Overview

Problem

Instrumentation amplifiers face challenges in achieving accurate low-frequency measurements with low noise and low power consumption, particularly in medical devices where discrete time architectures introduce aliasing and chopper-stabilized designs suffer from limited bandwidth and ripple issues.

Innovation Solution

A chopper-stabilized instrumentation amplifier with a differential architecture and a mixer amplifier that modulates and demodulates signals at a clock frequency, using feedback to eliminate noise and offset, operating as a continuous time system to minimize aliasing and reduce dynamic limitations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If a discrete time switched capacitor architecture is used, then the instrumentation amplifier can be implemented, but aliasing of noise and signals occurs undermining measurement accuracy

Engineering Contradiction:

Improveimplementation feasibilityVSAvoidmeasurement accuracy

Core Design Contradiction:

Ease of manufactureVSMeasurement precision

Solution Approach 1:

The patent replaces the discrete-time switched capacitor architecture with a continuous-time chopper-stabilized architecture. This substitution eliminates the sampling process that causes aliasing, thereby maintaining measurement accuracy while still enabling practical implementation of the instrumentation amplifier.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the operational mode from discrete-time sampling to continuous-time operation with periodic chopping. By modifying the time domain characteristics from sampled to continuous, the aliasing problem is eliminated while preserving the implementability of the amplifier structure.

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If a chopper stabilized architecture is used, then noise and offset are removed from the output signal, but the bandwidth is limited producing large ripple in the passband

Engineering Contradiction:

Improvenoise and offset eliminationVSAvoidbandwidth

Core Design Contradiction:

Measurement precisionVSSpeed

Solution Approach 1:

The patent employs dynamic chopping at low impedance nodes within the mixer amplifier, allowing the system to adaptively manage the trade-off between noise elimination and bandwidth. The chopping frequency and node selection are optimized to maintain adequate bandwidth while achieving effective noise and offset removal.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent uses feedback mechanisms to compensate for the ripple introduced by chopper stabilization. By feeding back the output signal and correcting for ripple components, the system maintains noise elimination benefits while reducing the detrimental effects of limited bandwidth and passband ripple.

Inventive Principle:

Principle #23Feedback

3Use of energy by moving object

If chopper stabilization is implemented at low power, then power consumption is reduced, but dynamic limitations such as glitching increase

Engineering Contradiction:

Improvepower consumptionVSAvoiddynamic performance

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

The patent introduces low impedance nodes as intermediary points for chopping within the mixer amplifier. These intermediary nodes allow chopping to be performed at points where the impedance is naturally low, reducing the dynamic stress and glitching that would otherwise occur during low-power operation, while still achieving the desired power reduction.

Inventive Principle:

Principle #24Intermediary (Mediator)

4Measurement precision

If instrumentation amplifiers require careful matching and trimming of circuit components, then high accuracy is achieved, but device complexity increases

Engineering Contradiction:

ImproveaccuracyVSAvoidcomponent matching and trimming

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent replaces the need for careful component matching and trimming with a chopper-stabilized architecture that inherently provides high accuracy. The chopping mechanism actively compensates for offset and drift errors, eliminating the need for precision component selection and manual trimming procedures, thereby reducing device complexity while maintaining high measurement accuracy.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentUS8354881B2Chopper-stabilized instrumentation amplifier

Publication Date: 2013.01.15 MEDTRONIC INC

AI summary

This disclosure describes a chopper stabilized instrumentation amplifier. The amplifier is configured to achieve stable measurements at low frequency with very low power consumption. The instrumentation amplifier uses a differential architecture and a mixer amplifier to substantially eliminate noise and offset from an output signal produced by the amplifier. Dynamic limitations, i.e., glitching, that result from chopper stabilization at low power are substantially eliminated through a combination of chopping at low impedance nodes within the mixer amplifier and feedback. The signal path of the amplifier operates as a continuous time system, providing minimal aliasing of noise or external signals entering the signal pathway at the chop frequency or its harmonics. The amplifier can be used in a low power system, such as an implantable medical device, to provide a stable, low-noise output signal.