Capacitive Charge Output A/D Conversion Without an Impedance Amplifier
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Solution Overview
Problem
In sensor devices with A/D converters, the need for an impedance converter and amplifier increases power consumption and size due to the high impedance of capacitive charge output devices, which complicates the conversion of analog signals to digital signals.
Innovation Solution
The integration of a capacitive adder defined by a series circuit including a capacitive charge output device and a capacitor, where the capacitive component of the output device is used to compute the difference between the analog input signal and the predicted value, eliminating the need for an impedance converter and amplifier, and utilizing a digital prediction filter to generate a predicted value that is used in Δ modulation for signal conversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an impedance converter and amplifier are provided to detect the output of the capacitive charge output device, then the signal can be properly detected and converted, but the power consumption increases and the device size increases
Solution Approach 1:
The capacitive charge output device's own capacitance is utilized as the integration capacitor in the ΔΣ modulator, allowing the device to serve dual purposes: generating charge and performing signal integration, thereby eliminating the need for separate amplifier and impedance converter components
Solution Approach 2:
The patent merges the function of the capacitive charge output device with the integration capacitor function by directly connecting the output of the charge device to the adder input, combining multiple functions into a single integrated structure that reduces component count and power consumption
2Reliability
If an impedance converter is provided between the capacitive charge output device and the adder, then impedance matching can be achieved, but the device complexity increases
Solution Approach 1:
The patent introduces a switching circuit as an intermediary element that controls the connection between the capacitive charge output device and the adder, enabling impedance management through controlled switching rather than requiring a dedicated impedance converter, thus simplifying the overall circuit structure
3Ease of manufacture
If additional components are added to handle the high impedance output, then signal conversion can be performed, but the manufacturing cost increases
Solution Approach 1:
The integration capacitor is designed to serve multiple functions: it acts as the feedback element in the ΔΣ modulator, performs signal integration, and can be controlled through switching to manage impedance and signal flow, thereby eliminating the need for separate dedicated components and reducing manufacturing complexity
Data Source
AI summary
A sensor device includes an A/D converter including an adder that computes a difference between an analog input signal and a predicted value, the adder includes a capacitive adder defined by a series circuit including a capacitive charge output device and a capacitor. A capacitive component in the charge output device defines a portion of the capacitance of the capacitive adder. A digital prediction filter generates the predicted value based on an output from a quantizer. The capacitive adder computes the difference between the analog input signal from the charge output device and the predicted value. The quantizer quantizes and encodes the difference. The A/D converter performs a Δ modulation on the analog input signal which is converted into a digital signal.