VCO Capacitance Sensing Without Charge Pump Biasing
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Solution Overview
Problem
Existing capacitance determination circuits for MEMS sensors require biasing references, leading to increased area and power consumption, and often necessitate high-voltage devices, which is inefficient and costly.
Innovation Solution
A capacitance determination circuit using a voltage controlled oscillator whose frequency depends on the control voltage across a capacitor, with a processing circuit generating an indication of capacitance based on frequency signals during charging and discharging phases, eliminating the need for high-voltage biasing and reducing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If biasing references with charge pumps are used for capacitance determination, then measurement capability is achieved, but chip area and power consumption increase
Solution Approach 1:
The patent extracts and eliminates the charge pump biasing reference from the capacitance determination circuit. Instead of using traditional charge pumps that require high-voltage devices, the invention uses a voltage-controlled oscillator whose frequency directly depends on the capacitor voltage, removing the need for separate biasing references and high-voltage components, thereby reducing chip area while maintaining measurement capability
Solution Approach 2:
The voltage-controlled oscillator serves multiple functions: it generates the frequency signal for capacitance measurement and simultaneously acts as the measurement mechanism itself. The oscillator's frequency naturally varies with capacitor voltage during charge/discharge phases, eliminating the need for separate biasing circuits and high-voltage devices, thus reducing overall circuit complexity and chip area
2Measurement precision
If biasing references with charge pumps are used for capacitance determination, then measurement capability is achieved, but power consumption increases
Solution Approach 1:
The patent removes the power-hungry charge pump biasing reference from the circuit. The voltage-controlled oscillator operates directly with the capacitor under test, using its natural frequency modulation in response to capacitor voltage changes. This eliminates the continuous power consumption associated with charge pump operation while maintaining accurate capacitance measurement capability
Solution Approach 2:
The voltage-controlled oscillator self-adjusts its frequency based on the capacitor voltage during charge and discharge phases without requiring external biasing references. The oscillator automatically tracks the capacitor's voltage state and converts it to frequency information, eliminating the need for additional power-consuming biasing circuits
3Measurement precision
If high-voltage devices are used for biasing references, then capacitance measurement is enabled, but device complexity and cost increase
Solution Approach 1:
The patent extracts and eliminates high-voltage devices from the capacitance determination circuit. By using a voltage-controlled oscillator that operates at standard voltages and whose frequency naturally depends on capacitor voltage, the invention removes the need for high-voltage transistors, special biasing references, and associated protection circuits, thereby reducing device complexity and manufacturing cost
Solution Approach 2:
The invention changes the operating parameters from high-voltage biasing to low-voltage frequency modulation. The voltage-controlled oscillator converts capacitor voltage variations directly into frequency variations, allowing capacitance measurement to be performed with standard-voltage components instead of requiring high-voltage devices, thus simplifying the overall circuit design
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 solution allows for efficient capacitance measurement with reduced chip area and power consumption, achieving high sensitivity and frequency modulation without the need for high-voltage components, while maintaining phase coherence and noise shaping.
Implementation Method 1
a voltage controlled oscillator configured to generate a frequency signal whose frequency depends on a control voltage supplied to the voltage controlled oscillator
Data Source
AI summary
According to an embodiment, a capacitance determination circuit is provided comprising a voltage controlled oscillator configured to generate a frequency signal whose frequency depends on a control voltage supplied to the voltage controlled oscillator, a capacitor coupled to the voltage controlled oscillator wherein the control voltage depends on a voltage across the capacitor and a processing circuit configured to generate, based on the frequency signal generated by the voltage controlled oscillator over a time interval comprising at least one phase in which the capacitor is charged and comprising at least one phase in which the capacitor is discharged, an indication of the capacitance of the capacitor.