Capacitive Sensor Readout Circuit for Low-Power Fast Sampling
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Solution Overview
Problem
Capacitive sensor devices in mobile or battery-operated devices face challenges in balancing low power consumption with sensitivity and responsiveness, as existing techniques often require overclocking, leading to adverse battery life and noise sensitivity issues.
Innovation Solution
A capacitive sensor device with a clock module, sensor module, and current supply module that employs a clock circuit to generate clock and sense signals, using an ADC to sample differences in capacitance, and a multiplier circuit to charge capacitors with bias current, optimizing sensitivity while minimizing power consumption by charging only during sampling and discharging between samples.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If sampling frequency is reduced to extend battery life, then power consumption decreases, but response time increases and user experience deteriorates
Solution Approach 1:
The patent implements periodic charging of the sense capacitor at regular intervals rather than continuous charging. The clock circuit generates periodic clock signals that trigger charging cycles, allowing the system to maintain sensing capability while consuming power only during discrete charging and sampling moments. This periodic operation mode directly addresses the contradiction by enabling the sensor to remain responsive without requiring continuous high-power operation.
Solution Approach 2:
The sense capacitor automatically discharges between charging cycles through its inherent leakage characteristics, eliminating the need for active discharge circuitry. The system leverages the natural self-discharge property of capacitors to reset the sensing element between measurements, reducing power consumption while maintaining operational readiness.
2Measurement precision
If conventional charging techniques are used, then capacitance measurement is achieved, but sensitivity is reduced due to noise and bias current variations
Solution Approach 1:
The patent introduces a sense capacitor as an intermediary element between the bias current source and the measurement circuitry. This sense capacitor acts as a buffer that integrates the bias current over time, converting current variations into voltage variations that can be measured by the ADC. The intermediary capacitor isolates the measurement system from direct exposure to bias current noise and voltage fluctuations, thereby improving measurement precision while reducing sensitivity to harmful electrical variations.
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 improved sensitivity and reduced power consumption by isolating the digitized readout from bias current variations, temperature, and noise, extending battery life while maintaining responsive capacitive sensor input detection.
Implementation Method 1
capacitive sensor devices, or devices which measure capacitance or a change in capacitance
Implementation Method 2
a clock module (102), a sensor module (104), and a current supply module (106)... a clock circuit (108) that is configured to receive a system clock (CK) and to generate a clock signal (CLK)
Implementation Method 3
a multiplier circuit to charge capacitors with bias current, optimizing sensitivity while minimizing power consumption
Data Source
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AI summary
A capacitive sensor device is provided. The capacitive sensor device may include a clock module configured to generate a clock signal, a sensor module configured to generate a reference signal and a sense signal, and sample a difference between the reference signal and the sense signal according to the clock signal, and a current supply module configured to selectively generate a bias current according to the clock signal, and charge each of the clock module and the sensor module based on the bias current and according to the clock signal.