Embedded Clock Oscillator Calibration Using CTMU Period Sensing
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Solution Overview
Problem
Integrated circuit devices face challenges in maintaining precise clock frequency accuracy over time, temperature, and voltage changes due to internal self-contained RC oscillators, which can drift due to package stress, fabrication, temperature, and voltage variations, especially in low pin count devices that rely on external crystals.
Innovation Solution
A frequency tunable internal clock oscillator system utilizing a Charge Time Measurement Unit (CTMU) with a capacitor and constant current source, coupled with an analog-to-digital converter and digital processor, automatically adjusts the clock frequency by comparing measured period times to reference values, allowing for precise frequency maintenance within 0.25% accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an external crystal is used to control clock frequency accuracy, then frequency precision is improved, but the number of package pins required increases
Solution Approach 1:
The patent extracts the frequency determination function from external components (crystal) and implements it internally using an RC oscillator with integrated frequency determination elements. This eliminates the need for external crystal connections while maintaining frequency control capability.
Solution Approach 2:
The internal RC oscillator circuit performs multiple functions: frequency generation, frequency determination, and self-calibration. The same internal circuitry that generates the clock signal also determines its own frequency and adjusts it through on-board tuning, eliminating the need for separate external frequency control components.
2Device complexity
If an internal self-contained RC oscillator is used to eliminate external pins, then package pin count is reduced, but frequency stability deteriorates due to drift from stress and environmental changes
Solution Approach 1:
The patent implements a feedback mechanism where the RC oscillator's output frequency is continuously monitored by frequency determination elements. The measured frequency is compared against a target value, and the difference drives an on-board tuning mechanism that adjusts the oscillator components (resistors, capacitors) to correct frequency drift, maintaining stability despite environmental variations.
Solution Approach 2:
The RC oscillator system performs self-calibration and self-adjustment using integrated on-board tuning elements. The circuit automatically detects frequency deviations caused by stress, temperature, or voltage changes and corrects them without external intervention, making the system self-regulating and stable.
3Measurement precision
If on-board tuning is implemented to maintain frequency accuracy, then frequency precision is improved, but device complexity increases
Solution Approach 1:
The patent merges the frequency determination elements, tuning components, and RC oscillator into a single integrated circuit block. The frequency determination circuitry, variable resistors, variable capacitors, and control logic are all combined within the same device, reducing overall system complexity despite the added tuning functionality.
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 system effectively maintains clock frequency accuracy over varying conditions, eliminating the need for external crystals and reducing pin requirements, ensuring reliable operation across temperature and voltage changes.
Implementation Method 1
a capacitor of known value and a constant current source of known value
Implementation Method 2
the voltage on the capacitor increases substantially linearly in time when the current steering switch couples the constant current source to the capacitor
Data Source
AI summary
Precision measurement of a period(s) of an embedded clock oscillator using a charge time measurement unit (CTMU) maintains a desired frequency accuracy of the embedded clock oscillator over a range of time, temperature and operating condition changes. The CTMU determines the free running frequency of the embedded clock oscillator and provides very accurate frequency (period) information for confirmation that a desired frequency, e.g., within 0.25 percent of the desired frequency, is running or an indication of how much and which direction to adjustment the frequency of the clock oscillator to maintain the frequency precision desired. Automatic frequency adjustment of the embedded clock oscillator may be implemented so as to maintain the desired precision frequency thereof. Temperature and voltage compensation profiles for maintaining the accuracy of the CTMU may be stored in a table, e.g., nonvolatile memory, for a further improvement in absolute frequency accuracy of the embedded clock oscillator.