Crystal Oscillator Module for Low-Jitter Bus Synchronization
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Solution Overview
Problem
Current synchronous systems face challenges in coordinating clock signals across multiple components and boards, leading to increased jitter, noise, and reduced reliability due to the need for central clocks, phase-locked loops, and fanout buffers, while asynchronous systems sacrifice high performance for scalability and redundancy.
Innovation Solution
A crystal oscillator-based module with a conditioning circuit, sustaining stage amplifier, gain control network, synchronization range expansion circuit, and tri-state buffer is used to receive and output sync signals between two buses, eliminating the need for central clocks and phase-locked loops, and providing redundancy and scalability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a central clock is distributed across the circuit, then clock coordination is achieved, but system complexity and cost increase
Solution Approach 1:
The patent divides the system into multiple independent clock domains, with each board or module having its own local crystal oscillator. This segmentation eliminates the need for a single central clock distribution network, reducing system complexity while maintaining reliable clock coordination through autonomous local oscillators that can operate independently yet synchronize when needed.
2Manufacturing precision
If PLLs are used to eliminate skew between fanout outputs, then clock skew is reduced, but jitter increases
Solution Approach 1:
The patent extracts the phase-skew correction function from the clock distribution network itself and implements it locally at each receiver using delay-locked loops (DLLs) that adjust only the phase alignment. This removes the need for PLLs in the fanout path, eliminating the jitter generation while still achieving skew compensation through local phase adjustment rather than centralized frequency locking.
3Speed
If clock frequency is multiplied at each component, then data rate is achieved, but jitter increases as square of multiplication factor
Solution Approach 1:
The patent performs frequency multiplication in advance at a centralized clock source before distribution, rather than multiplying at each remote component. The locally generated crystal oscillator provides a clean base frequency that is then distributed as-is or with minimal processing. This preliminary action at the source avoids the cumulative jitter that would result from multiple distributed multiplication operations, while still achieving the required data rates through the clean, low-jitter clock signal.
4Adaptability or versatility
If asynchronous architecture is adopted, then scalability and redundancy improve, but performance decreases
Solution Approach 1:
The patent implements a dynamic clock architecture where each module operates as an autonomous clock domain with its own crystal oscillator, providing the scalability and redundancy of asynchronous systems. However, the system dynamically switches between independent operation and synchronized operation when high-performance communication between modules is required, thus achieving both scalability and high performance by adapting the level of synchronization to the operational requirements.
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 reduces system costs, improves phase noise and jitter performance, and enables 'hot-swapping' and smooth power-up sequences by using a higher Q, less expensive crystal resonator and alternating connections of SXO modules, preventing self-synchronization and ensuring synchronized RF outputs.
Implementation Method 1
A crystal resonator is connected so as to receive the conditioned signal and so as to output a resonator signal
Data Source
AI summary
A crystal oscillator-based module, which includes a crystal resonator receiving a conditioned signal from a first bus and passing a resonator signal to a sustaining stage amplifier. A synchronization range expansion circuit is connected between a gain control network and the resonator. A tri-state buffer has a main input connected to receive the resonator signal through a buffer. The output of the tri-state buffer is connected to a second bus, through a matching network if necessary. A synchronous clock system can be formed by connecting these modules alternately to the two busses. The tri-state buffer also has a control input, which may be connected to a delay circuit between Vcc and ground, so as to allow hot swapping and for other benefits.