Sensor Charge Generator Using Parasitic Capacitance for Accurate Compensation
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Solution Overview
Problem
Conventional switched capacitor (SC) charge generators in sensor arrangements face limitations due to disturbing charges generated by switching elements, which affect the compensation charge needed to balance sensor charges, especially at lower light intensities where the compensation charge is weak.
Innovation Solution
The proposed sensor arrangement utilizes the parasitic capacitor of a transistor as a storage element to generate compensation charge, with a control circuit managing the conductivity of transistors to alternately charge and discharge this capacitor, and includes a compensation component to counteract disturbing charges caused by switching operations, along with a controllable reference voltage generator to stabilize the compensation current against temperature and process variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional switched capacitor circuit with dedicated charge storage elements is used, then the charge generator can provide compensation charge, but switching elements generate disturbing charges that affect the compensation accuracy
Solution Approach 1:
The patent converts the harmful charge injection effect into a useful function by using the parasitic capacitor of the first transistor to store compensation charge. The charge injection that was previously a disturbance is now the mechanism for transferring compensation charge to the output node, eliminating the need for separate charge storage elements and reducing the impact of disturbing charges on compensation accuracy
Solution Approach 2:
The patent extracts the charge storage function from dedicated capacitor elements and integrates it into the parasitic capacitor of the first transistor. This removes the separate charge storage element that would be subject to disturbing charges, and uses only the necessary switching elements (first and second transistors) for charge transfer control
2Illumination intensity
If the compensation charge is reduced to handle lower light intensities, then the sensor can detect weaker signals, but the disturbing charges from switching elements become stronger relative to the compensation charge
Solution Approach 1:
By using the parasitic capacitor for charge storage and transfer, the patent ensures that even at very low compensation charge levels (corresponding to weak light intensities), the charge injection effect serves to transfer the compensation charge accurately to the output node without being overwhelmed by disturbing charges from separate storage elements
Solution Approach 2:
The patent changes the operating parameters by using the inherent parasitic capacitance of the first transistor rather than a dedicated capacitor, allowing the system to maintain accurate compensation even when the compensation charge magnitude is very small, thus enabling detection of weaker light intensities
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 approach effectively reduces the unwanted influence of disturbing charges, ensuring accurate compensation of sensor currents by using the parasitic capacitor for charge storage and a reference loop to control the compensation current, applicable to both optical and non-optical sensors.
Implementation Method 1
the parasitic capacitor of the first transistor of the charge generator is used as a storage element to store a respective compensation charge portion during subsequent switching cycles of the first and the second transistor
Data Source
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AI summary
A sensor arrangement to sense an external signal comprises a sensor (100) and a charge generator (200) to generate a compensation current (Ic) to compensate the sensor current. A charge generator (200) comprises a first transistor (210) having a parasitic capacitor (212) and a first conductive path. The charge generator (200) comprises a second transistor (220) having a second conductive path being coupled in series to the first transistor (210) and coupled to the output node (O200) of the charge generator (200). The control circuit (600) is configured to control the conductivity of the respective first and second conductive path of the first and the second transistor (210, 220) of the charge generator (200) so that the sensor current is compensated by the compensation current (Ic).