Continuous-Time Chopper Amplifier for Low-Aliasing Impedance Measurement
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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 have limited bandwidth and ripple issues.
Innovation Solution
A chopper-stabilized instrumentation amplifier with a differential architecture and a mixer amplifier that uses 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.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a discrete time switched capacitor architecture is used, then the instrumentation amplifier can obtain discrete signal samples, 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 low-noise performance through chopper stabilization techniques.
Solution Approach 2:
The patent introduces a chopper circuit as an intermediary that modulates the measurement signal into a higher frequency band before processing. This intermediary stage removes low-frequency noise and offset through frequency translation, while the continuous-time operation avoids aliasing issues inherent in discrete-time systems.
2Measurement precision
If a chopper stabilized architecture is used, then noise and offset are removed from the output signal, but the bandwidth is limited and large ripple is produced in the passband
Solution Approach 1:
The patent modifies the chopper-stabilized architecture by changing the operating parameters and circuit topology to extend the bandwidth. This includes optimizing the modulator and demodulator stages to operate effectively over a wider frequency range while maintaining noise rejection capabilities.
Solution Approach 2:
The patent employs dynamic compensation techniques and feedback mechanisms that adapt to the chopper frequency to minimize ripple in the passband. The circuit dynamically adjusts to maintain stability and reduce ripple across the extended bandwidth, rather than being fixed at a single operating point.
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 occur
Solution Approach 1:
The patent implements feedback mechanisms that monitor and correct for glitches caused by low-power chopper operation. The feedback path detects dynamic limitations and compensates for them in real-time, maintaining reliable operation while preserving low power consumption characteristics.
Solution Approach 2:
The patent incorporates preprocessing stages and circuit design elements that anticipate and prevent glitching before it occurs. By designing the chopper circuit to inherently minimize dynamic limitations from the outset, the system maintains reliability without requiring excessive power for correction.
Data Source
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.