Hybrid RC-Crystal Oscillator for Fast Start-Up and Accuracy
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Solution Overview
Problem
Microcontrollers face challenges with oscillator start-up times, reliability, and accuracy, as external crystal oscillators add cost, take longer to start-up, and require additional device pins, while internal RC oscillators lack precision and stability over temperature ranges.
Innovation Solution
A hybrid RC/crystal oscillator design that incorporates a tunable internal RC oscillator and an external crystal as a supplementary clock source, allowing for phase detection and frequency adjustment to achieve phase lock, providing a reliable and flexible clock source with fast start-up and high signal integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an external crystal oscillator is used, then accuracy is improved, but start-up time increases and device complexity increases
Solution Approach 1:
The internal RC oscillator is activated and running before the external crystal oscillator is needed, providing immediate clock signal during start-up. The system performs preliminary frequency adjustment and phase detection setup while the crystal is still settling, enabling faster transition to crystal-based operation.
Solution Approach 2:
The internal RC oscillator serves as an intermediary clock source during the transition period. It provides a provisional clock signal that allows the system to initialize while the external crystal oscillator is coming up, bridging the gap between immediate operation and precise crystal-based operation.
2Measurement precision
If an external crystal oscillator is used, then accuracy is improved, but device complexity increases
Solution Approach 1:
The internal RC oscillator circuit is designed to serve dual purposes: as the primary clock source during start-up and as a tunable frequency source for phase detection and frequency adjustment. This multi-functionality eliminates the need for separate circuitry, reducing overall device complexity despite the presence of external crystal support.
Solution Approach 2:
The frequency adjustment circuit and phase detection circuit are integrated with the internal RC oscillator, combining multiple functions into a unified system. The RC oscillator is merged with the external crystal oscillator through phase detection, creating a hybrid system that achieves crystal accuracy without requiring a complete external crystal oscillator implementation.
3Measurement precision
If an external crystal oscillator is used, then accuracy is improved, but the number of pins required increases
Solution Approach 1:
The external crystal is connected to shared oscillator pins that also serve the internal RC oscillator. The same pins are used for both the internal RC oscillator output and the external crystal connection, allowing the system to achieve external crystal accuracy without requiring dedicated additional pins for crystal connection.
4Speed
If an internal RC oscillator is used, then start-up speed is improved, but accuracy deteriorates
Solution Approach 1:
The internal RC oscillator provides immediate start-up capability while simultaneously performing preliminary frequency adjustment. The system uses the RC oscillator to initialize and then quickly adjusts its frequency through phase detection against the external crystal, achieving both fast start-up and accurate operation.
Solution Approach 2:
A phase detection circuit provides feedback to the frequency adjustment circuit, which continuously monitors the phase difference between the internal RC oscillator and the external crystal oscillator. This feedback mechanism allows the RC oscillator to self-adjust its frequency to match the crystal reference, achieving crystal-level accuracy while maintaining the fast start-up characteristics of the RC oscillator.
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 hybrid oscillator retains the reliability and quick-startup of internal RC oscillators while achieving the accuracy of external crystal oscillators, offering frequency flexibility, fault-tolerance, and reduced pin usage, with the ability to seamlessly fallback to internal oscillation during external crystal failures.
Implementation Method 1
a phase detector circuit communicatively coupled with an output of the tunable oscillator and an input to the oscillator
Implementation Method 2
an oscillator controller circuit configured to adjust frequency of the tunable oscillator based upon phase detection between output of the tunable oscillator and output of an external resonant element, such as a crystal
Data Source
AI summary
An oscillator includes a tunable oscillator, a phase detector circuit communicatively coupled with an output of the tunable oscillator and an input to the oscillator, and an oscillator controller circuit configured to adjust frequency of the tunable oscillator based upon phase detection between output of the tunable oscillator and output of an external resonant element received at the input to the oscillator.