Chopper Amplifier Circuit for Low-Power Physiological Signal Gain
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Solution Overview
Problem
Medical devices face challenges in amplifying low frequency physiological signals, particularly in implantable devices with limited power resources, where low voltage signals with encoded information at low frequencies are difficult to amplify without introducing significant noise.
Innovation Solution
The use of a chopper amplifier with an amplification and transconductance unit, comprising complementary transistors, to amplify low frequency signals while increasing transconductance and reducing power consumption, thereby minimizing offset noise and 1/f noise, and incorporating a demodulation unit to generate a chopper-stabilized amplified signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional amplifiers are used to amplify low frequency physiological signals, then signal amplification is achieved, but offset noise and 1/f noise increase significantly
Solution Approach 1:
The patent applies chopper modulation which periodically switches the amplifier operation between different states. The input signal is modulated to a higher frequency, amplified, then demodulated back to baseband. This periodic action moves the signal away from the 1/f noise region during amplification, significantly reducing offset and flicker noise in the output signal.
Solution Approach 2:
The patent introduces an intermediary modulation stage that converts the low frequency physiological signal to a higher frequency carrier signal before amplification. This intermediary frequency translation allows the amplifier to operate in a region with lower noise characteristics, then the intermediary demodulation stage converts it back while preserving the signal information.
2Object-affected harmful factors
If transconductance is increased to reduce thermal noise, then noise performance improves, but power consumption increases
Solution Approach 1:
The patent changes the operating frequency parameter by modulating the signal to a higher frequency before amplification. This parameter change allows the use of lower transconductance values to achieve the same noise performance, thereby reducing power consumption while maintaining thermal noise specifications.
Solution Approach 2:
The periodic chopper modulation allows the amplifier to achieve high effective transconductance during the active phases while maintaining lower average power consumption. The modulated signal spends part of its cycle in high-gain states and part in reset or low-power states, reducing overall power requirements.
3Duration of action of stationary object
If power consumption is reduced for implantable device longevity, then device duration extends, but signal amplification capability deteriorates
Solution Approach 1:
The chopper amplifier architecture uses periodic modulation and demodulation cycles that allow the amplifier to achieve high gain during brief active intervals while remaining in low-power states during reset intervals. This periodic operation enables adequate signal amplification for physiological signals while maintaining average power consumption suitable for implantable devices.
Solution Approach 2:
The patent changes the frequency parameter of the signal to a higher modulated frequency, which allows the amplifier to achieve the required signal-to-noise ratio with lower power consumption. This parameter transformation enables the amplifier to maintain measurement precision while operating in a lower power regime appropriate for implantable applications.
Data Source
AI summary
In an example, an electrical circuit device for amplifying a physiological signal includes a modulation unit configured to receive an input signal, to modulate the input signal to produce a modulated signal. The device also includes an amplification and transconductance unit configured to amplify an amplitude of the modulated signal and increase a transconductance of the modulated signal to produce a transconductance enhanced modulated and amplified signal, where the amplification and transconductance unit comprises at least a first complementary pair of transistors and a second complementary pair of transistors configured to receive the modulated signal and to amplify and increase the transconductance of the modulated signal. The device also includes a demodulation unit configured to receive the transconductance enhanced modulated and amplified signal and to demodulate the signal.