Mixed-Signal IC Capacitance Sensing Through High-Cutoff Frequency
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Solution Overview
Problem
Existing CMOS biosensors face challenges in accurately measuring small capacitance variations in the femto-Farad range due to parasitic capacitance, with current methods like Capacitance to Voltage Converters (CVC) and Capacitance to Frequency Converters (CFC) facing limitations in sensitivity and power consumption.
Innovation Solution
A method involving a capacitance to pulse width conversion (CPC) technique that measures capacitance changes by detecting high cutoff frequency variations using identical voltage amplifiers with reference capacitors, converting these variations into discernible electrical signals through a frequency sweep and difference detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Capacitance to Voltage Converters (CVC) or Capacitance to Frequency Converters (CFC) are used to measure capacitance variations, then capacitance measurement capability is achieved, but measurement precision deteriorates due to parasitic capacitance in the femto-Farad range
Solution Approach 1:
The patent introduces an intermediary measurement approach by converting capacitance variations into high cutoff frequency variations of an amplifier. Instead of directly measuring capacitance (which is affected by parasitic capacitance), the system uses the amplifier's frequency response as an intermediary that is more sensitive to small capacitance changes. The high cutoff frequency serves as a mediator that translates tiny capacitance variations into measurable frequency shifts, thereby overcoming the limitations of direct capacitance measurement methods.
2Measurement precision
If high sensitivity measurement methods are employed to detect femto-Farad capacitance variations, then measurement precision improves, but power consumption increases
Solution Approach 1:
The patent changes the measurement parameter from direct capacitance measurement to high cutoff frequency measurement. By sweeping the frequency range and identifying the high cutoff frequency point, the system achieves high sensitivity to capacitance variations. This parameter transformation allows the use of a simpler, lower-power amplifier-based measurement approach instead of complex, high-power conversion circuits, thereby achieving both high precision and low power consumption.
3Measurement precision
If Capacitance to Frequency Converters (CFC) are used to convert capacitance variations to frequency, then frequency variation can be used as target detection indicator, but device complexity increases
Solution Approach 1:
The patent merges the capacitance sensing function with the amplifier's frequency response characteristics. Instead of using a separate CFC circuit to convert capacitance to frequency, the system combines the sensing capacitor directly with the amplifier, making the amplifier's own frequency response the measurement mechanism. This integration eliminates the need for separate conversion circuits, reducing overall device complexity while maintaining the ability to detect capacitance variations through frequency measurement.
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
Enables detection of capacitance variations as low as 1 fF with improved sensitivity and reduced power consumption, suitable for life science applications such as cell growth monitoring and DNA detection.
Implementation Method 1
detecting a high cutoff frequency of a voltage amplifier connected to the sensing capacitor and determining a difference from a reference high cutoff frequency as a measure of the capacitance change or difference
Data Source
AI summary
In a preferred embodiment, there is provided a method for measuring a capacitance change or difference of a sensing capacitor, the method comprising: sweeping a frequency range of first and second alternating current (AC) voltage sources respectively connected to first and second amplifiers, said first amplifier having or connected to a first reference capacitor or electrode and said second amplifier having or connected to a second reference capacitor or electrode and the sensing capacitor; detecting first and second high cutoff frequencies respectively of the first and second amplifiers; and determining a difference between the first and second high cutoff frequencies, wherein the difference reflects the capacitance change or difference.