Chopper-Stabilized Mixer Amplifier for Low-Aliasing Impedance Sensing
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Solution Overview
Problem
Instrumentation amplifiers face challenges in achieving stable, low-noise measurements at low frequencies with low power consumption, particularly in medical devices where noise and offset issues are prevalent, and existing solutions like discrete time switched capacitor architectures suffer from aliasing, while chopper-stabilized designs have limited bandwidth and ripple issues.
Innovation Solution
A chopper-stabilized instrumentation amplifier with a differential architecture and a mixer amplifier that combines chopping at low impedance nodes and feedback to eliminate noise and offset, operating as a continuous time system to minimize aliasing and achieve stable measurements at low frequencies with very low power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a discrete time switched capacitor architecture is used, then the amplifier can be constructed with discrete components, but it produces undesirable aliasing of noise and signals
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, while maintaining the ability to achieve low offset and noise through chopper stabilization techniques.
Solution Approach 2:
The patent introduces a chopper circuit as an intermediary that modulates the measurement signal to a higher frequency band before amplification. This intermediary stage prevents noise and offset from being amplified directly, thereby eliminating aliasing while allowing discrete component construction.
2Measurement precision
If a chopper stabilized architecture is used, then noise and offset are removed by up-modulating the signal, but the bandwidth is limited and large ripple is produced in the passband
Solution Approach 1:
The patent employs dynamic element matching and switching techniques within the chopper-stabilized architecture to broaden the bandwidth. By dynamically adjusting circuit parameters and using switching capacitors at optimized timing, the system achieves both noise removal and extended frequency response with reduced passband ripple.
3Measurement precision
If chopper stabilization is implemented, then offset and noise are eliminated, but power consumption increases
Solution Approach 1:
The patent uses periodic chopping at optimized frequencies to achieve offset and noise elimination with reduced power consumption. By synchronizing the chopping frequency with the signal characteristics and using periodic resetting of integrators, the system achieves stabilization without continuous high-power operation.
Solution Approach 2:
The patent optimizes the chopping frequency and amplifier gain parameters to minimize power consumption while maintaining offset and noise elimination. By adjusting these parameters based on signal conditions, the system achieves low-power operation with high measurement precision.
Data Source
AI summary
In general, this disclosure is directed to a mixer amplifier that can be utilized within a chopper stabilized instrumentation amplifier. The chopper stabilized instrumentation amplifier may be used for physiological signal sensing, impedance sensing, telemetry or other test and measurement applications. In some examples, the mixer amplifier may include a current source configured to generate a modulated current at a modulation frequency for application to a load to produce an input signal, an amplifier configured to amplify the input signal to produce an amplified signal, and a demodulator configured to demodulate the amplified signal at the modulation frequency to produce an output signal indicating an impedance of the load.