Oscillator Circuit with Kalman Filtering for Aging Correction
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Solution Overview
Problem
Existing oscillators, such as OCXO and TCXO, face challenges in accurately monitoring and correcting long-term variations in oscillation frequency due to aging, which are difficult to follow in a short time with high accuracy, especially when transitioning from a non-holdover to a holdover state.
Innovation Solution
A circuit device that performs Kalman filter processing on phase comparison results between an oscillation signal and a reference signal, with adaptive noise variance settings and cutoff frequency adjustments, allowing for accurate estimation and aging correction of oscillation frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional aging correction methods are used to monitor long-term oscillation frequency variations, then aging correction can be provided, but it is difficult to follow the long-term variation in a short time and to estimate a time change of a small value with high accuracy
Solution Approach 1:
The patent applies dynamics by making the cutoff frequency of the loop filter variable rather than fixed. The cutoff frequency is dynamically adjusted based on the holdover state: a first (higher) cutoff frequency is used during normal operation for fast response, and a second (lower) cutoff frequency is used during holdover state for high measurement precision. This dynamic adjustment resolves the contradiction between fast convergence and high estimation accuracy.
Solution Approach 2:
The patent changes the parameter of cutoff frequency based on operational conditions. By switching between different cutoff frequency values depending on whether the system is in holdover state or not, the system optimizes both response speed and measurement precision for different operational phases, thereby resolving the trade-off between convergence time and estimation accuracy.
2Reliability
If a fixed cutoff frequency is used for the loop filter, then the circuit structure is simple, but it cannot achieve both fast convergence and high accuracy in different operational states
Solution Approach 1:
The loop filter's cutoff frequency is made dynamic by switching between two values based on the holdover state. This dynamic configuration allows the system to optimize reliability for aging correction by using appropriate cutoff frequencies for different operational states, while the complexity increase is minimal since it only requires state detection and frequency switching logic.
Solution Approach 2:
The cutoff frequency parameter is changed based on operational conditions (holdover state). This parameter adaptation enables the system to achieve high reliability in aging correction by selecting optimal frequency values for different states, with the added complexity being limited to the switching mechanism triggered by state changes.
Data Source
AI summary
A circuit device includes a processing circuit and an oscillation signal generation circuit. The processing circuit performs Kalman filter processing for a result of phase comparison between an input signal based on an oscillation signal and a reference signal and performs loop filter processing for the result of phase comparison. The oscillation signal generation circuit generates the oscillation signal of an oscillation frequency set by frequency control data which is output data of the loop filter processing by using the frequency control data and a resonator. The processing circuit estimates a truth value for an observed value of the result of phase comparison by using the Kalman filter processing.