Chopper-Precharge Sensor Circuit for Low-Noise A/D Sampling
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Solution Overview
Problem
Existing physical quantity detection circuits face challenges in reducing noise levels and improving the accuracy of digital signal output due to 1/f noise generated by operational amplifiers in buffer circuits, which affects the input signal of A/D conversion circuits.
Innovation Solution
Incorporating a precharge circuit with operational amplifiers and chopper circuits between the passive filter and A/D conversion circuit, which synchronizes chopping operations with sampling to reduce 1/f noise and precharge the input capacitance effectively, thereby enhancing the signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a buffer circuit is used to precharge the input capacitance of the A/D conversion circuit, then the sampling accuracy is improved, but the noise level increases due to 1/f noise from operational amplifiers
Solution Approach 1:
The patent extracts and removes the harmful 1/f noise component from the buffer circuit output by using a chopper circuit that modulates the noise to a higher frequency range, separating it from the low-frequency signal band, thereby allowing the signal to be preserved while the noise is filtered out
Solution Approach 2:
The chopper circuit acts as an intermediary between the buffer circuit and the A/D conversion circuit, transforming the 1/f noise into high-frequency noise through frequency modulation, which then can be effectively removed by the low-pass filter while maintaining the precharging function
2Object-generated harmful factors
If the driving capability of the passive low-pass filter is increased to reduce noise, then the noise level decreases, but the circuit complexity and power consumption increase
Solution Approach 1:
The patent replaces the need for a high-driving-capability active filter with a passive low-pass filter combined with a chopper circuit system, substituting mechanical/electrical amplification with frequency domain transformation and filtering, thereby reducing circuit complexity and power consumption while maintaining noise reduction effectiveness
3Speed
If the buffer circuit precharges the input capacitance, then the sampling speed is improved, but the signal-to-noise ratio deteriorates
Solution Approach 1:
The chopper circuit performs periodic switching at a frequency much higher than the signal frequency, creating periodic noise modulation that allows the signal to be distinguished from noise through frequency separation, maintaining both fast sampling and high signal-to-noise ratio
Solution Approach 2:
The patent changes the frequency parameter of the noise through chopper modulation, transforming 1/f noise into high-frequency noise, thereby altering the noise characteristics to be compatible with both fast sampling requirements and high signal-to-noise ratio requirements
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration reduces noise levels and improves the accuracy of digital signal output by minimizing gain reduction and noise interference, resulting in a higher signal-to-noise ratio for physical quantity sensors.
Implementation Method 1
a first chopper circuit that is provided in a signal path between the passive filter and the operational amplifier, and a second chopper circuit that is provided in a signal path between the operational amplifier and the analog/digital conversion circuit, and the first chopper circuit and the second chopper circuit perform a chopping operation
Implementation Method 2
the precharge circuit includes an operational amplifier, a first chopper circuit that is provided in a signal path between the passive filter and the operational amplifier
Implementation Method 3
a passive filter that receives a first analog signal based on an output signal of a physical quantity detection element
Implementation Method 4
an analog/digital conversion circuit that includes an input capacitance and converts a result obtained by sampling a second analog signal based on an output signal of the passive filter at the input capacitance into a digital signal
Data Source
AI summary
A physical quantity detection circuit includes a passive filter that receives a first analog signal based on an output signal of a physical quantity detection element, an analog/digital conversion circuit, and a precharge circuit that includes an operational amplifier, a first chopper circuit provided between the passive filter and the operational amplifier, and a second chopper circuit provided between the operational amplifier and the input capacitance of the analog/digital conversion circuit and precharges an input capacitance of the analog/digital conversion circuit, the first and the second chopper circuits perform a chopping operation in synchronization with an operation that the analog/digital conversion circuit samples the second analog signal at the input capacitance, based on an output signal of the passive filter.