Charge Amplifier Leakage Correction for Stable Force Sensing
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Solution Overview
Problem
Conventional charge amplifiers, such as those described in JP-A-11-148878, face issues with leakage current variations affecting output signal characteristics due to potential differences between the source and drain of FETs, leading to potential signal drift and saturation, which can impair continuous operation in applications like force sensors and robots.
Innovation Solution
A charge amplifier configuration that includes a leakage current correction circuit with a series connection of a resistance circuit and a switch, controlled by a control circuit to cancel at least part of the leakage current flowing through the integration circuit, thereby reducing signal drift and maintaining stable output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a diode is provided with a reverse bias in an input line to cancel leakage current, then leakage current is compensated, but the leakage current of the FET varies with potential difference between source and drain, causing output signal characteristics to be affected
Solution Approach 1:
The patent introduces a feedback mechanism where the control circuit monitors the potential difference between source and drain of the FET and dynamically adjusts the diode's reverse bias current to match the FET's leakage current. This closed-loop feedback ensures that the compensation adapts to varying operating conditions, maintaining accurate leakage current cancellation without affecting output signal characteristics
Solution Approach 2:
The patent dynamically changes the reverse bias parameters of the diode based on the measured potential difference across the FET. By adjusting the reverse bias current as a variable parameter rather than a fixed value, the system adapts to changing operating conditions, ensuring continuous accurate leakage current compensation while maintaining stable output signal characteristics
2Device complexity
If the leakage current of FET is not corrected, then the circuit structure remains simple, but signal drift and saturation occur, impairing continuous operation
Solution Approach 1:
The patent introduces a diode as an intermediary component that generates a compensating current to counteract the FET's leakage current. This intermediary element acts as a mediator between the power supply and the integration circuit, providing continuous leakage current compensation that enables prolonged continuous operation without signal drift or saturation
Solution Approach 2:
The control circuit automatically monitors and adjusts the diode's reverse bias to compensate for FET leakage current variations, enabling the system to self-correct without external intervention. This self-service mechanism ensures continuous operation by automatically preventing signal drift and saturation conditions
Data Source
AI summary
A charge amplifier includes: an input line thorough which an electric charge signal is propagated; an integration circuit including an input terminal coupled to the input line and an output terminal that outputs the voltage signal; a reset switch configured to reset the voltage signal by closing between the input terminal and the output terminal; a leakage current correction circuit including a first resistance circuit and a first switch coupled in series in this order between a first node, which has a first potential different from a potential of the input line, and the input line; and a control circuit configured to control the first switch based on the voltage signal so as to cancel at least a part of a leakage current flowing through the integration circuit.