Temperature-Compensated Oscillator Filtering for Low Phase Noise
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Solution Overview
Problem
Noise from temperature sensors in temperature compensated oscillators degrades the phase noise of the oscillator output, and existing filters struggle to balance noise rejection and tracking performance, particularly in integrated circuits where low bandwidth filtering is challenging.
Innovation Solution
A novel low pass filter design using techniques from control theory, with a transfer function that includes at least two poles at the origin and additional poles and zeros, is implemented in the digital domain to reduce noise and improve tracking performance, decoupling noise rejection and tracking characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a low bandwidth filter is used to reduce noise in the temperature compensation signal, then phase noise is reduced, but tracking performance during rapid temperature changes deteriorates
Solution Approach 1:
The filter bandwidth is made dynamically adjustable rather than fixed. The system switches between a first filter bandwidth for normal operation and a second, wider filter bandwidth during rapid temperature changes. This dynamic adaptation allows the system to optimize between noise reduction and tracking performance based on real-time temperature conditions.
Solution Approach 2:
The system periodically monitors temperature变化 rate and adjusts the filter bandwidth accordingly. When rapid temperature changes are detected, the system switches to a wider bandwidth mode temporarily, then returns to the narrower bandwidth mode when conditions stabilize. This periodic monitoring and adjustment enables the system to handle transient conditions while maintaining optimal noise filtering during steady-state operation.
2Object-affected harmful factors
If a narrow bandwidth filter is used to reject noise, then noise rejection improves, but the filter introduces delay that causes tracking errors
Solution Approach 1:
The filter bandwidth is dynamically adjusted based on temperature change conditions. During rapid temperature changes, the system switches to a wider bandwidth that reduces group delay and tracking errors. During stable temperature conditions, the system uses a narrower bandwidth for optimal noise rejection. This dynamic bandwidth adjustment resolves the trade-off between noise rejection and tracking delay.
Solution Approach 2:
The system changes the filter parameter (bandwidth) based on operating conditions. By monitoring the temperature变化 rate and adjusting the filter bandwidth accordingly, the system optimizes both noise rejection and tracking performance. This parameter adaptation allows the filter to maintain low group delay during transient conditions while achieving high noise rejection during steady-state operation.
3Reliability
If the filter bandwidth is increased to improve tracking during rapid temperature changes, then tracking performance improves, but noise rejection deteriorates
Solution Approach 1:
The system periodically monitors temperature conditions and temporarily increases filter bandwidth only when rapid temperature changes are detected. This periodic monitoring ensures that the wider bandwidth (which provides better tracking) is used only when necessary, while the narrower bandwidth (which provides better noise rejection) is used during normal operation. This temporal separation of functions resolves the contradiction.
4Device complexity
If a fixed filter bandwidth is used, then device complexity is reduced, but the system cannot adapt to varying temperature conditions
Solution Approach 1:
The system implements dynamic bandwidth adjustment by switching between two predefined filter configurations based on temperature change conditions. This approach provides adaptability to varying temperature conditions while maintaining relatively simple device complexity, as it uses a switched configuration rather than a continuously adjustable filter. The system monitors temperature变化 rate and automatically selects the appropriate bandwidth mode.
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 filter design achieves improved noise rejection and tracking performance, reducing phase noise and enhancing the robustness of temperature compensation, especially during rapid temperature changes, while maintaining stability and ease of manufacture.
Implementation Method 1
the temperature compensation module comprises a low pass filter configured to reduce noise in the temperature compensation signal
Implementation Method 2
based on an output from a temperature sensor
Implementation Method 3
an oscillator circuit to drive a piezoelectric resonator such as a quartz crystal
Implementation Method 4
The frequency of such oscillators is governed by the quartz crystal
Data Source
AI summary
Temperature compensated oscillators are provided. The oscillator comprises an oscillator circuit and a temperature compensation module. The temperature compensation module reduces temperature induced errors in the frequency of oscillation of the oscillator by providing a temperature compensation signal to the oscillator circuit based on a temperature sensor output. The temperature compensation module comprises a low pass filter configured to reduce noise in the temperature compensation signal. The low pass filter is such that, using Laplace representations of transfer functions, the transfer function H(s) of the filter is equivalent to the transfer function of a closed loop configuration in which a module having an open loop transfer function G(s) is configured to generate an output from the closed loop configuration by applying the open loop transfer function G(s) to an error between an input to the closed loop configuration and the output from the closed loop configuration.