Crystal Oscillator Amplitude-Controlled Startup for ESR Variation
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Solution Overview
Problem
The design of crystal oscillators for high-frequency applications, such as 60 GHz wireless systems, faces challenges in accommodating a wide range of Equivalent Series Resistance (ESR) values, leading to potential crystal damage or failure due to excessive drive levels, and requires multiple circuit designs or customer-specific crystals, increasing costs and complexity.
Innovation Solution
A control loop and mixed-signal controlled power supply multi-path resistive array are used to provide a large gain for quick startup of the crystal oscillator, with a successive approximation ADC to tailor power routing and minimize 'l/f' noise, ensuring the crystal is not overdriven and maintaining steady-state phase noise performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If a large gain inverter is used to start oscillation quickly, then the startup time is reduced, but the drive level becomes excessive and may damage the crystal
Solution Approach 1:
The patent implements a dynamic control mechanism where the inverter gain is adjusted based on real-time amplitude detection. During startup, high gain is applied to achieve quick oscillation establishment. Once oscillation reaches steady state, the gain is automatically reduced to prevent excessive drive level. This dynamic adjustment resolves the contradiction between fast startup and crystal protection.
Solution Approach 2:
The patent employs an amplitude detector that continuously monitors the oscillation amplitude and feeds this information back to control the inverter gain. The feedback loop ensures that the drive level remains within safe limits while enabling fast startup by initially allowing high gain. This closed-loop control system simultaneously achieves both fast startup and crystal protection.
2Duration of action of stationary object
If the drive level is limited to protect the crystal, then crystal lifetime is extended, but the oscillation startup becomes slow or fails to start
Solution Approach 1:
The patent applies preliminary high gain to the inverter during the startup phase to ensure rapid oscillation establishment. Once oscillation is achieved and reaches adequate amplitude, the gain is then reduced to protective levels. This preliminary action of high gain during startup, followed by reduction to protective levels, simultaneously achieves fast startup and crystal protection.
Solution Approach 2:
The patent implements periodic monitoring of oscillation amplitude with automatic gain adjustment. During the startup period, high gain is maintained to ensure rapid oscillation. After startup completion is detected, the gain is periodically adjusted to maintain oscillation while protecting the crystal. This periodic control resolves the contradiction between fast startup and crystal lifetime extension.
3Device complexity
If a fixed circuit design is used, then manufacturing complexity is reduced, but compatibility with various crystal ESR values is limited
Solution Approach 1:
The patent implements a universal circuit design that can accommodate a wide range of crystal ESR values through dynamic gain control. The amplitude detector and feedback mechanism enable the same circuit to adapt to different crystal characteristics without requiring design variations. This universal approach maintains manufacturing simplicity while achieving broad crystal compatibility.
Solution Approach 2:
The patent changes the operating parameters of the inverter dynamically based on detected oscillation amplitude and crystal characteristics. By adjusting the gain parameter in response to amplitude feedback, the circuit adapts to different crystal ESR values. This parameter change mechanism enables a single circuit design to work with various crystals while maintaining manufacturing simplicity.
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
This approach allows the crystal oscillator to start up quickly while preventing mechanical breakdown, extends crystal lifetime, and reduces 'l/f' noise, making it compatible with various crystals and reducing the need for multiple circuit designs or customer-specific crystals.
Implementation Method 1
Quartz crystals oscillate under the influence of an electric field or can generate electric fields if exposed to stress
Implementation Method 2
An amplitude detector measures an amplitude of the oscillating signal
Data Source
AI summary
A large gain is used to start up the oscillation of the crystal quickly. Once the oscillation starts, the amplitude is detected. A control circuit determines based on the measured amplitude to disable a low resistance path in the controlled switch array to reduce the applied gain below the power dissipation specification of the crystal. Another technique introduces a mixed-signal controlled power supply multi-path resistive array which tailors the maximum current to the crystal. A successive approximation register converts the amplitude into several partitions and enables/disables one of several power routing paths to the inverter of the oscillator. This allows a better match between the crystal selected by the customer and the on-chip drive circuitry to power up the oscillator without stressing the crystal. The “l/f” noise of the oscillator circuit is minimized by operating transistors in the triode region instead of the linear region.