RC Oscillator Self-Calibration Using Capacitor Voltage Measurement
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Solution Overview
Problem
Existing calibration methods for internal RC oscillators in microcontrollers require external reference signals, leading to increased production costs, additional hardware, and computational burdens, as well as the need for recalibration upon power cycles without non-volatile memory.
Innovation Solution
A method and system for calibrating internal RC oscillators using an RC circuit with a resistor and capacitor, where the capacitor is charged and discharged to measure voltage levels, allowing for self-calibration without external reference signals, with adjustments made to the clock frequency based on comparisons to a threshold voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If external reference signals are used for calibration, then clock frequency accuracy is improved, but device complexity and production cost increase
Solution Approach 1:
The microcontroller performs self-calibration by using its own internal RC oscillator to generate calibration signals and measure its own frequency deviation. The system charges a capacitor through a resistor using internally generated clock cycles, then measures the voltage to determine frequency accuracy, eliminating the need for external reference signals or additional calibration hardware.
Solution Approach 2:
The invention extracts the calibration function from the external domain and implements it entirely within the microcontroller's internal resources. By removing the dependency on external reference signals and external calibration circuits, the system achieves frequency calibration using only internal oscillators, capacitors, and control logic already present in the microcontroller.
2Measurement precision
If external reference signals are used for calibration, then clock frequency accuracy is improved, but production cost increases
Solution Approach 1:
The microcontroller performs self-calibration by using its own internal RC oscillator to generate calibration signals and measure its own frequency deviation. The system charges a capacitor through a resistor using internally generated clock cycles, then measures the voltage to determine frequency accuracy, eliminating the need for external reference signals and external calibration hardware, thereby reducing production costs.
Solution Approach 2:
The invention uses inexpensive internal RC oscillator components and simple RC circuits that can be easily manufactured and integrated into mass-produced microcontrollers. By replacing expensive external crystal oscillators and calibration equipment with cheap internal RC-based self-calibration circuitry, the system achieves cost-effective frequency calibration suitable for mass production.
3Measurement precision
If recalibration is performed after power down without non-volatile memory, then calibration accuracy is maintained, but additional hardware is required
Solution Approach 1:
The microcontroller performs self-calibration by using its own internal RC oscillator to generate calibration signals and measure its own frequency deviation. The system charges a capacitor through a resistor using internally generated clock cycles, then measures the voltage to determine frequency accuracy, eliminating the need for external reference signals and external calibration hardware.
4Ease of manufacture
If internal RC oscillators are used, then production cost is reduced, but clock frequency stability deteriorates
Solution Approach 1:
The invention implements a feedback-based self-calibration mechanism where the microcontroller measures the actual frequency of its internal RC oscillator by timing capacitor charging cycles, compares it against the expected frequency, and adjusts the oscillator's operation accordingly. This closed-loop feedback system compensates for temperature drift and manufacturing variations, maintaining frequency stability without requiring expensive external crystal oscillators.
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 approach reduces production costs and hardware requirements, enabling reliable self-calibration of internal RC oscillators, eliminating the need for external reference signals and minimizing recalibration procedures, while maintaining clock frequency stability across varying environments.
Implementation Method 1
adjusting voltage to a first voltage level across a capacitor of a RC circuit connected to said microcontroller chip; inputting a reference voltage signal for fixed number of clock cycles in said capacitor; measuring a second voltage level across said capacitor after a predetermined duration
Data Source
AI summary
To calibrate an oscillator for microcontroller chip operation, an RC circuit is coupled to the microcontroller circuitry and a voltage signal is applied to the capacitor for changing the voltage across the capacitor. The voltage value across the capacitor is measured and compared to an expected voltage value. Adjustments to the frequency of the clock signal generated by the oscillator are made in response to the comparison.