Integrated Electric Field Sensor Bootstrapping
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing electric field sensors face challenges in achieving high input impedance due to internal capacitance and noise issues, particularly with discrete amplifier designs that require complex calibration and are prone to parasitic capacitance and leakage, making it difficult to maintain low-noise, high-impedance measurements.
Innovation Solution
An integrated amplifier with bootstrapped input transistor and active shield within the sensor, eliminating external conductive biasing and ESD protection, allowing for higher impedance, lower noise, and reduced capacitance, and enabling operation as a floating gate with non-volatile charge initialization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If discrete operational amplifiers are used in electric field sensors, then the sensor can be constructed with commercially available components, but the input impedance is degraded due to internal capacitance (2-10 pF) and the sensor requires complex neutralization circuits with manual calibration
Solution Approach 1:
The patent merges the discrete amplifier with the sensor electrode into a single integrated unit, eliminating the need for separate neutralization circuits. The amplifier is positioned so close to the electrode that its input capacitance is effectively included in the sensor's total capacitance, which is then neutralized by a single capacitor connected to the amplifier output, simplifying the circuit while maintaining high input impedance
Solution Approach 2:
The patent introduces a bootstrap capacitor as an intermediary element that connects the amplifier output back to the amplifier input. This capacitor, combined with the feedback resistor, creates a bootstrapping effect that cancels out the amplifier's input capacitance, thereby maintaining high input impedance without requiring complex external neutralization circuits
2Measurement precision
If active shielding is used to raise sensor input impedance, then packaging and circuit board level capacitance is minimized, but internal amplifier capacitance remains inaccessible and contributes 2-10 pF to input capacitance
Solution Approach 1:
The patent merges the amplifier physically and electrically with the sensor electrode, positioning the amplifier so close that its input terminals are effectively at the sensor location. This integration makes the amplifier's internal capacitance accessible and includable in the overall sensor capacitance model, allowing it to be neutralized along with other parasitic capacitances
Solution Approach 2:
The patent employs feedback by connecting a capacitor from the amplifier output back to the amplifier input (bootstrap capacitor). This feedback mechanism creates a bootstrapping effect that dynamically cancels the amplifier's input capacitance, converting what would be an inaccessible harmful capacitance into a controllable parameter that can be neutralized
3Measurement precision
If neutralization circuits are implemented to overcome internal input capacitance, then high impedance can be achieved, but manual calibration and tuning are required and additional power supplies with greater voltage range are needed
Solution Approach 1:
The patent combines the neutralization function with the amplifier's existing feedback network by using the same feedback resistor and adding a bootstrap capacitor. This integration eliminates the need for separate neutralization circuits and their associated manual calibration procedures, as the bootstrapping effect automatically compensates for input capacitance across operating conditions
Solution Approach 2:
The feedback network in the integrated amplifier serves multiple functions simultaneously: it provides the necessary amplification feedback, implements the bootstrapping effect to neutralize input capacitance, and stabilizes the amplifier operation. This multi-functionality eliminates the need for separate neutralization circuits and additional power supplies
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 solution achieves significantly higher input impedance (>50 TΩ) and lower noise (0.05 fA/(Hz)1/2) compared to prior art, eliminating the need for neutralization and manual calibration, while maintaining stable operation with a lower power supply, and effectively measuring electric fields with improved signal fidelity.
Implementation Method 1
at least one sensing electrode for detecting an electric field and generating an input signal
Implementation Method 2
at least another terminal of each circuit element is connected to a signal that substantially follows the active shield so that the plurality of circuit elements connected to the sensor input are substantially bootstrapped
Data Source
AI summary
An electric field sensor includes one or more sensing electrodes connected to an integrated amplifier that bootstraps all parasitic capacitances at the sensor input to provide for a very high input impedance without the need for neutralization or other adjustments and calibration. The integrated amplifier for the electric field sensor further includes low-noise ESD/biasing structures to stabilize the DC-potential of the sensor with a minimum amount of added noise, leakage and parasitic capacitance.