Chopper Amplifier Circuit for Low-Frequency Signal Attenuation
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Solution Overview
Problem
Conventional chopper amplification circuits struggle to amplify low-frequency input signals due to parasitic capacitance, leading to signal attenuation and inability to operate effectively at low power supply voltages, which is essential for reducing power consumption in modern devices.
Innovation Solution
The proposed signal amplification circuit employs a chopper amplifier with a differential single amplifier and a control signal generator to perform chopper modulation and demodulation, using switches to manage parasitic capacitance and maintain a constant voltage difference, thereby preventing signal attenuation and enabling amplification of low-frequency signals even at low voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a chopper amplification circuit is used to amplify sensor signals, then the signal quality is improved by reducing 1/f noise, but low-frequency input signals are attenuated due to parasitic capacitance
Solution Approach 1:
The input stage is segmented into two separate amplification paths: a chopper amplification path for high-frequency signals and a non-chopper amplification path for low-frequency signals. This segmentation allows each path to be optimized for its specific frequency range, preventing the parasitic capacitance of the chopper amplifier from attenuating low-frequency signals while still providing 1/f noise reduction for high-frequency signals.
2Use of energy by moving object
If the power supply voltage is decreased to reduce power consumption, then energy efficiency is improved, but CMOS analog switches block intermediate voltage level signals
Solution Approach 1:
Different switching mechanisms are used for different parts of the circuit: the input stage uses transmission gate switches that can handle intermediate voltage levels, while other stages use conventional CMOS switches. This local differentiation allows the circuit to operate at low voltages while preventing blocking of intermediate voltage signals at the critical input stage.
3Use of energy by stationary object
If a capacitance feedback-type chopper amplification circuit is used to enable low voltage operation, then power consumption is reduced, but low-frequency input signals cannot be amplified due to parasitic capacitance attenuation
Solution Approach 1:
A non-chopper operational amplifier is introduced as an intermediary component to handle low-frequency signal amplification. This intermediary amplifier is positioned in parallel with the chopper amplifier, receiving low-frequency signals that would otherwise be attenuated by the chopper amplifier's parasitic capacitance, and providing a separate amplification path that does not suffer from this limitation.
Data Source
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AI summary
A signal amplification circuit (41) includes an input terminal; a first chopper modulation circuit (12); a first amplifier (14) including an amplification circuit (140) and a chopper demodulation circuit (15) connected to a second output terminal of the amplification circuit (14), a capacitance feedback circuit (170), including a second chopper modulation circuit (18), connected to an output terminal of the chopper demodulation circuit (15) to an input terminal of the amplification circuit (140) via a feedback point, a first switch (SW0e, SW0f), connected to a first output terminal of the amplification circuit (15), constituting a voltage follower circuit with the amplification circuit (15); a second switch (SW0a, SW0b, SW0c, SW0d); a second amplifier (21) to convert an amplified signal from the second output terminal of the amplification circuit (140) into a single-end signal; and a filter (22, 24) to pass at least a predetermined frequency component of a chopping frequency from the single-end signal output from the second amplifier (21) to output an output signal.