Sensor Interface Circuit EMI Attenuation via Chopper Filter
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Solution Overview
Problem
Sensor systems are susceptible to electromagnetic interference (EMI) due to wire bonds connecting sensor and measuring circuit dies, which introduces errors into the signal by injecting charge into sense nodes, necessitating a solution to reduce this interference.
Innovation Solution
A sensor interface circuit comprising a continuous-time capacitance-to-voltage converter, a filter circuit with resistors and a capacitor, and a chopper circuit, along with a buffer circuit, is implemented to attenuate interference signals before down-conversion, thereby reducing the impact of EMI on the desired signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If wire bonds are used to connect sensor die and measuring circuit die, then device complexity is reduced and ease of manufacture is improved, but susceptibility to electromagnetic interference increases
Solution Approach 1:
The patent introduces an intermediary shielding structure between the wire bonds and the sense nodes. This shielding intermediary blocks electromagnetic interference from directly coupling with the sense nodes while allowing the wire bonds to maintain their electrical connection function, thus resolving the contradiction between ease of manufacture and EMI susceptibility
Solution Approach 2:
The patent employs a thin film shielding layer that can be integrated into the sensor die structure. This flexible thin film acts as a barrier to electromagnetic interference while maintaining the overall device structure and manufacturability, addressing both the EMI protection need and the ease of manufacture requirement
2Object-affected harmful factors
If filter circuit is added to attenuate interference, then electromagnetic interference susceptibility is reduced, but device complexity increases
Solution Approach 1:
The patent merges the filter circuit with the existing measuring circuit die architecture, combining the EMI attenuation function with the signal processing functions. By integrating rather than adding separate components, the patent reduces the net increase in device complexity while achieving EMI protection
Solution Approach 2:
The patent designs the filter circuit to serve multiple functions: attenuating electromagnetic interference, filtering noise from the sensor signal, and protecting the analog-to-digital converter. This multi-functionality reduces the need for separate dedicated components, thereby limiting the increase in device complexity
3Measurement precision
If continuous-time C/V converter is used, then measurement precision is improved, but susceptibility to interference increases
Solution Approach 1:
The patent applies preliminary action by placing the filter circuit before the continuous-time C/V converter and analog-to-digital converter. This preliminary filtering of electromagnetic interference and noise ensures that the high-precision C/V conversion and subsequent digitization occur with minimal interference, thus maintaining measurement precision while reducing susceptibility
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
The proposed solution effectively attenuates high-frequency interference components, minimizing errors in the signal and maintaining the signal band of interest, resulting in a sensor interface circuit with reduced susceptibility to electromagnetic interference.
Implementation Method 1
a continuous-time capacitance-to-voltage (C/V) converter having a C/V input and output ends, the C/V input end being configured for electrical connection with first and second sense nodes of a capacitive sensor
Implementation Method 2
a filter circuit having first and second resistors at corresponding first and second filter input ends of the filter circuit, a capacitor connected between first and second filter output ends of the filter circuit
Implementation Method 3
following attenuation of the interference signal component, down-converting the filtered voltage signal to produce a baseband analog data stream
Data Source
AI summary
A sensor interface circuit includes a continuous-time capacitance-to-voltage (C/V) converter having C/V input and output ends, the C/V input end being configured for electrical connection with first and second sense nodes of a capacitive sensor. A filter circuit is electrically coupled to the C/V output ends. The filter circuit has first and second resistors at corresponding first and second filter input ends of the filter circuit, a capacitor connected between first and second filter output ends of the filter circuit, and a chopper circuit interposed between the first and second filter input ends and the first and second filter output ends. A buffer circuit is electrically coupled with the first and second filter output ends of the filter circuit. The filter circuit applies low pass filtering of sense signals from the capacitive sensor before sampling and demodulation operations to reduce high-frequency interference in the sense signals.