LC Oscillator Clock Generation Without External Crystals
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Solution Overview
Problem
Crystal-based clock generators are costly, occupy significant printed circuit board area, and are susceptible to frequency deviations due to mechanical stresses from temperature changes, making them incompatible with modern CMOS integrated circuit manufacturing technologies and prone to phase jitter.
Innovation Solution
A clock generator comprising a free-running LC oscillator and a tunable frequency synthesizer, which compensates for operational changes by using measured characteristics like temperature and manufacturing process variations, eliminating the need for external crystals and achieving precise frequency control without additional noise or complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If external crystals are used to generate precise clock signals, then frequency precision is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent extracts the frequency reference function from external crystals and implements it using an on-chip ring oscillator. The ring oscillator generates a base frequency that is then divided and synthesized to achieve the required clock frequencies, eliminating the need for external crystal components while maintaining frequency precision through digital synthesis techniques.
Solution Approach 2:
The patent creates a universal clock generation system that can produce multiple clock frequencies from a single ring oscillator source. The frequency synthesizer and divider network enable the same core oscillator to generate various clock signals for different functional blocks within the integrated circuit, reducing overall system complexity.
2Stability of the object's composition
If external crystals are used for clock generation, then frequency stability is improved, but manufacturing compatibility worsens
Solution Approach 1:
The patent replaces the mechanical resonance system of external crystals with an electronic ring oscillator implemented in CMOS technology. The ring oscillator uses transistor-based delay elements that can be manufactured using standard CMOS fabrication processes, eliminating the need for separate crystal mounting and bonding operations.
Solution Approach 2:
The patent merges the clock generation function directly into the integrated circuit chip by implementing the ring oscillator and frequency synthesis logic in the same CMOS process. This integration eliminates the need for external crystal components and their associated mounting structures, simplifying the manufacturing process.
3Measurement precision
If external crystals are used to generate clock signals, then frequency accuracy is improved, but phase jitter increases
Solution Approach 1:
The patent introduces digital frequency synthesis and division circuits as intermediary stages between the ring oscillator and the final clock outputs. These intermediary circuits use synchronous division and phase-locked loop techniques to clean up phase noise and reduce jitter while maintaining frequency accuracy through digital control.
4Measurement precision
If external crystals are used for clock generation, then frequency precision is improved, but cost increases
Solution Approach 1:
The patent replaces expensive external crystal components with a cost-effective ring oscillator implementation using standard CMOS transistors. The ring oscillator achieves sufficient frequency precision for the application without requiring precision-trimmed crystal resonators, significantly reducing component costs.
Solution Approach 2:
The patent combines the clock generation function with the main integrated circuit logic, eliminating the need for separate external crystal components and their associated mounting hardware. This integration reduces both component costs and assembly costs.
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 solution provides a cost-effective, compact, and accurate clock signal generation, comparable to crystal-based generators, with reduced phase jitter and temperature sensitivity, suitable for modern integrated circuit manufacturing processes.
Implementation Method 1
a free-running LC oscillator having an output for providing an oscillator clock signal
Implementation Method 2
The tunable frequency synthesizer is coupled to the free-running oscillator and provides a clock output signal in response to the oscillator clock signal and a frequency control signal, where the frequency control signal corresponds to a measured characteristic of the free-running oscillator
Data Source
AI summary
A clock generator comprises a free-running oscillator and a tunable frequency synthesizer. The free-running oscillator has an output for providing an oscillator clock signal. The tunable frequency synthesizer is coupled to the free-running oscillator and provides a clock output signal in response to the oscillator clock signal and a frequency control signal. The frequency control signal corresponds to a measured characteristic of the free-running oscillator.