Low-Power Capacitor Sensor Array With Switched-Capacitor Readout
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Solution Overview
Problem
Conventional capacitive sensors face challenges with scalability due to area and power consumption limitations, parasitics, and large errors in frequency and jitter, often using complex RF voltage-controlled oscillators and inductance-based techniques that lead to unwanted oscillations and non-linear detection.
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 temperature-compensated ADC to measure fully settled voltage values, enhancing scalability and reducing clock jitter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional RF voltage-controlled oscillators and inductance-based techniques are used, then capacitive sensing can be achieved, but power consumption and area increase significantly
Solution Approach 1:
The patent extracts and removes the RF VCO and inductor components from the capacitive sensing system, replacing them with a simplified switched-capacitor circuit that uses only capacitors and switches. This extraction eliminates the high power consumption associated with RF oscillators while maintaining the capacitive sensing function through direct charge transfer measurement.
Solution Approach 2:
The patent substitutes the electromagnetic RF oscillation-based measurement system with a direct electrical charge transfer system. Instead of using RF VCOs that generate electromagnetic oscillations to detect capacitance changes, the invention uses switched-capacitor circuits that directly transfer and measure charge, replacing a complex electromagnetic system with a simpler electrical measurement approach.
2Measurement precision
If multiple inductors and capacitors are used in conventional methods, then capacitive sensing is enabled, but ASIC area increases
Solution Approach 1:
The patent merges the functions of multiple inductors and capacitors into a single integrated switched-capacitor circuit. The demultiplexer/multiplexer topology allows a single receiver to handle multiple sensor elements, and the switched-capacitor architecture combines charge transfer, signal conditioning, and measurement functions into one compact circuit block, dramatically reducing the required ASIC area.
Solution Approach 2:
The receiver circuit in the patent is designed with universal functionality to handle multiple sensor elements through the demultiplexer/multiplexer topology. A single receiver can sequentially or simultaneously measure multiple capacitive sensors by switching connections, eliminating the need for dedicated receiver circuits for each sensor element and thus reducing overall ASIC area.
3Measurement precision
If conventional VCO-based methods are used, then frequency-based detection is achieved, but clock jitter and measurement errors increase
Solution Approach 1:
The patent uses simple switched-capacitor circuits with basic switches and capacitors instead of complex, expensive RF VCOs. These simpler components are less prone to drift and jitter, providing more reliable measurements. The switched-capacitor approach uses straightforward charge transfer that can be accurately measured without the frequency stability issues inherent in VCO-based systems.
4Use of energy by stationary object
If demultiplexer/multiplexer topology with common driver and receiver is used, then area and power are reduced, but device complexity increases
Solution Approach 1:
The patent employs dynamic switching through the demultiplexer/multiplexer topology, where connections are dynamically reconfigured based on which sensor element is being measured. The switches dynamically connect different sensor elements to the common receiver at different times, enabling a single receiver to serve multiple sensors. This dynamic approach reduces the need for static duplicate circuits, lowering power consumption while the switching control logic manages the complexity.
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 reduced power consumption, area, and improved performance with 12-13 bit resolution, providing uniform detection across a range and avoiding the use of RF antennas and VCOs, thus minimizing power dissipation and error.
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 driver device having first input configured to receive clock signal, second input configured to receive charging voltage, third input configured to receive common-mode voltage, and output; first capacitor configured to be sensed, having first terminal connected to output of driver device and second terminal; and receiver device having first input configured to receive clock signal, second input connected to second terminal of first capacitor, and third input configured to receive the common mode voltage, wherein the receiver includes a temperature-compensated analog-to-digital converter (ADC), wherein the temperature-compensated ADC includes a voltage reference generator, and wherein the voltage reference generator includes a comparator, a first p-channel Metal Oxide Semiconductor (MOS) transistor, a second p-channel MOS transistor, a third p-channel MOS transistor a first variable resistor, a second variable resistor, a third variable resistor, a fourth variable resistor, a first diode, and a second diode.