Switched-Capacitor Sensor Array for Low-Power Capacitance Detection
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Solution Overview
Problem
Conventional capacitive sensors face challenges in scalability due to area and power consumption limitations, parasitics, and large errors in frequency and jitter, with complex RF voltage-controlled oscillators and inductance-based techniques leading to undesirable effects and non-linear detection outcomes.
Innovation Solution
A low-power capacitor sensor array utilizing a demultiplexer/multiplexer topology with a common driver and receiver, coupled with a switched capacitor architecture, reduces the number of driver and receiver devices, eliminates RF antennas and VCOs, and employs a high-resolution temperature-compensated ADC for accurate detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional RF voltage-controlled oscillators and inductance-based techniques are used for capacitive sensing, then detection capability is achieved, but power consumption and area increase significantly
Solution Approach 1:
The patent extracts and removes the RF VCO and inductor components from the sensing system, replacing them with a simplified switched-capacitor architecture that uses only capacitors and switches. This extraction eliminates the high power consumption associated with RF oscillators while maintaining capacitance detection capability through charge transfer measurements.
Solution Approach 2:
The patent uses capacitor arrays to create multiple copies of the sensing element, allowing parallel or sequential measurement of different capacitance values. By copying the basic capacitor-switch structure rather than using complex RF circuitry, the system achieves scalable detection with low power consumption.
2Measurement precision
If multiple inductors and capacitors are used in conventional methods, then detection function is provided, but ASIC area becomes larger reducing scalability
Solution Approach 1:
The patent merges multiple sensing functions into a single integrated capacitor array structure. Instead of using separate inductors and capacitors for each sensing element, the invention combines all sensing functionality into an array of capacitors that can be measured sequentially or in parallel through multiplexing, dramatically reducing the required ASIC area.
Solution Approach 2:
The capacitor array structure serves multiple functions: it acts as both the sensing element and the storage element for charge transfer. The same capacitor structure is used for all measurement points in the array, providing universal functionality that eliminates the need for separate dedicated components at each sensing location.
3Measurement precision
If conventional VCO-based methods are used, then capacitance measurement is achieved, but frequency errors and jitter increase due to parasitics
Solution Approach 1:
The patent replaces the RF electromagnetic oscillation mechanism with a purely electronic charge transfer mechanism. Instead of measuring capacitance through frequency modulation of an RF oscillator, the invention directly measures charge transfer between capacitors using switched-capacitor circuits and ADCs, eliminating all frequency-related parasitics and jitter issues.
4Measurement precision
If RF VCOs are used for sensing, then detection is enabled, but the system becomes non-linear and uncertain
Solution Approach 1:
The patent replaces the non-linear RF VCO operation with linear switched-capacitor charge transfer. The charge transferred between capacitors is directly proportional to the capacitance ratio and input voltage, providing inherently linear operation that simplifies signal processing and improves measurement accuracy without requiring complex linearization techniques.
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 reduces power consumption, area, and improves scalability while achieving 12-13 bit resolution and uniform detection across a range, minimizing clock jitter and parasitic effects.
Implementation Method 1
utilizes a switched-capacitor method for transferring charge on an array capacitor being sensed to a capacitor in a receiver
Data Source
AI summary
A capacitive sensor and capacitive sensing method including a driver device having a first input configured to receive a clock signal, a second input configured to receive a charging voltage, a third input configured to receive a common-mode voltage, and an output; a first capacitor configured to be sensed, having a first terminal connected to the output of the driver device and a second terminal; and a receiver device having a first input configured to receive the clock signal, a second input connected to the second terminal of the first capacitor, and a third input configured to receive the common mode voltage.