Self-Calibrated On-Chip Oscillator for Accurate Clock Frequency
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Solution Overview
Problem
Existing clock generators, such as crystal oscillators, are not integrated into microprocessors, leading to increased space and production costs, and lack the accuracy required for sophisticated electronics due to frequency drift, jitter, and noise sensitivity.
Innovation Solution
An automatic self-calibrated oscillation method and apparatus using a STT table, RTT table, processing unit, signal conversion circuit, and oscillation circuit that calibrate the output clock signal to maintain a tunable target frequency by comparing current and reference RTT values, adjusting for deviations to ensure accuracy across variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If crystal oscillators are used for accurate clock generation, then frequency accuracy is improved, but integration with microprocessor is prevented and space requirements increase
Solution Approach 1:
The patent merges the crystal oscillator functionality with the microprocessor by integrating a calibration circuit and lookup tables directly into the processor chip. The system combines the benefits of crystal oscillator accuracy with on-chip integration by measuring actual operating frequency under various PVT conditions and storing calibration data in on-chip memory, eliminating the need for separate clock ICs while maintaining high frequency accuracy.
2Measurement precision
If crystal oscillators are used for accurate clock generation, then frequency accuracy is improved, but manufacturing costs and production complexity increase
Solution Approach 1:
The patent combines multiple functions (oscillation, calibration, measurement, and storage) into a single integrated circuit package. By implementing the calibration system entirely on-chip with the microprocessor, the design eliminates the need for separate clock generator ICs, reducing assembly steps, lowering manufacturing costs, and simplifying production while maintaining frequency accuracy through on-chip calibration.
3Area of stationary object
If integrated clock generators are used to reduce space, then area requirements are reduced, but frequency accuracy and stability deteriorate due to PVT variations
Solution Approach 1:
The patent applies preliminary calibration by pre-measuring and storing the actual operating frequencies at various PVT conditions in lookup tables during manufacturing. This preliminary characterization allows the system to compensate for PVT variations during operation by selecting appropriate calibration values, maintaining frequency accuracy without requiring additional space for external calibration components.
Solution Approach 2:
The system implements feedback by continuously monitoring the relationship between target frequencies and actual operating frequencies using stored calibration data. The calibration circuit uses this feedback information to adjust frequency settings, compensating for PVT variations and maintaining accurate clock generation within the compact on-chip design.
4Device complexity
If traditional oscillators are used without calibration, then device complexity is reduced, but frequency drift and jitter increase under PVT variations
Solution Approach 1:
The patent performs preliminary calibration by measuring and storing actual frequency characteristics at various PVT conditions during manufacturing. This pre-characterization creates a database of calibration values that the system uses to compensate for environmental variations, achieving frequency stability without requiring complex real-time calibration circuits or algorithms.
Solution Approach 2:
The system creates a digital copy of the frequency characteristics by storing measured PVT-dependent frequency data in lookup tables. This digital representation allows the calibration circuit to retrieve and apply appropriate correction values during operation, achieving frequency stability through software-based compensation rather than complex hardware circuits.
Data Source
AI summary
An automatic self-calibrated oscillation method and an apparatus using the same are provided. After a static time tuning (STT) table and a run time tuning (RTT) table have been established, the apparatus converts an output clock signal to generate a current RTT value at every predefined time and then compares the current RTT value with a reference RTT value generated in response to a STT value of the STT table, or with an interpolated result generated in response to the reference RTT value to generate a deviation value. Thus, through the deviation value, the output clock signal may be calibrated to address the target frequency without the assistance of external reference clock unit or locked loop unit after the STT table and the RTT table are established.