RC Oscillator Calibration Using Chopped Period Averaging
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Solution Overview
Problem
Existing methods for determining and calibrating RC time constants in electronic circuits are prone to errors due to mismatches in current sources and comparator delays, affecting the accuracy of RC time constant measurement.
Innovation Solution
An RC oscillator is operated in two configurations to determine the RC time constant by averaging the periods of the oscillator output signals, which helps to average out errors caused by current source mismatches and comparator delays, and a calibration routine is performed to adjust capacitance to achieve a desired period.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single configuration measurement method is used to determine RC time constant, then the measurement process is simple, but the measurement precision deteriorates due to errors from current source mismatches and comparator delays
Solution Approach 1:
The measurement process is segmented into two distinct configurations: Configuration 1 measures the period with current source I1 charging the capacitor, while Configuration 2 measures the period with current source I2 charging the capacitor. By dividing the measurement into separate configurations and averaging the results, the patent eliminates systematic errors from current source mismatches and comparator delays, thereby improving measurement precision without significantly increasing overall process complexity
Solution Approach 2:
The patent employs periodic switching between two measurement configurations. The oscillator alternates between Configuration 1 and Configuration 2, measuring periods T1 and T2 respectively. This periodic action allows the system to collect multiple measurements under different conditions and average them, which cancels out periodic errors from comparator delays and current source variations, enhancing measurement accuracy
2Reliability
If variable resistances and capacitances are implemented for calibration, then the RC time constant can be calibrated, but the device complexity increases
Solution Approach 1:
The patent calibrates the RC time constant by changing the capacitance parameter of the oscillator. A capacitor array with switchable configurations allows the capacitance value to be adjusted in discrete steps. By measuring the oscillation period at different capacitance values and interpolating to find the capacitance that produces the desired period, the system achieves precise RC time constant calibration without requiring variable resistors, thereby limiting the increase in device complexity
Solution Approach 2:
The patent creates multiple copies of the measurement and calibration circuitry for different RC time constant values. Instead of using complex variable components, the design replicates the oscillator circuit with different fixed capacitor values and uses switching to select between them. This copying approach simplifies the calibration mechanism while maintaining the ability to achieve precise RC time constant values through selection and interpolation
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 method provides a more accurate determination and calibration of the RC time constant, reducing errors and ensuring precise operation of electronic circuits by averaging out the errors from current source mismatches and comparator delays.
Implementation Method 1
the capacitor may charge until the voltage across the capacitor exceeds the voltage across the resistor, causing a discharge circuit to activate to discharge the capacitor
Implementation Method 2
An RC time constant is a value, measure in units of time, indicating the amount of time required to charge a capacitor to approximately 63.2% of its full charge through a resistor
Data Source
AI summary
A method and apparatus for determining an RC (resistive-capacitive) time constant is disclosed. In one embodiment, a method comprises determining a first period of oscillation when an oscillator is operating in a first configuration. The method further comprises determining a second period of oscillation when the oscillator is operating in a second configuration. A measurement circuit is configured to determine a resistive-capacitive (RC) time constant of the oscillator by determining a mean of the first and second periods.