Free-Running Oscillator Frequency Tuning Without a Reference Clock
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Solution Overview
Problem
Integrated circuits often lack high-precision oscillators, limiting their use and requiring high-cost solutions, especially in applications where precise frequency control is necessary without an internal reference clock.
Innovation Solution
A free-running oscillator circuitry with a frequency adjustment mechanism that uses synchronization pulses to adaptively adjust its frequency, eliminating the need for an internal reference clock and allowing the oscillator to operate independently once the target frequency is achieved.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a free-running oscillator is used without an internal reference clock, then device complexity and cost are reduced, but frequency accuracy deteriorates (typically greater than 2% error)
Solution Approach 1:
The patent implements a feedback mechanism where the oscillator frequency is continuously monitored by counting pulses over a defined period, comparing the count to an expected value, and adjusting the frequency based on the difference. This closed-loop feedback system enables the free-running oscillator to achieve high frequency accuracy (within 1-5%) without requiring an internal reference clock, thus resolving the contradiction between reduced device complexity and improved frequency accuracy
Solution Approach 2:
The patent dynamically changes the oscillator's operating parameters (frequency) based on measured performance. By monitoring the actual pulse count and comparing it to the expected count, the system adjusts frequency control parameters to minimize the difference, thereby achieving high accuracy through parameter optimization rather than through complex hardware design
2Reliability
If synchronization pulses are used frequently to maintain frequency accuracy, then frequency stability is improved, but loss of time and increased device complexity occur
Solution Approach 1:
The patent employs periodic synchronization pulses at optimized intervals to maintain frequency accuracy. Rather than continuous adjustment, the system uses periodically triggered pulse trains to measure and adjust the oscillator frequency, achieving reliable frequency stability while minimizing the time overhead associated with synchronization operations
Solution Approach 2:
The patent applies partial synchronization by using synchronization pulses only when necessary to correct frequency drift, rather than continuous synchronization. The system monitors frequency accuracy and applies correction only when the difference between actual and expected pulse counts exceeds acceptable thresholds, thereby maintaining stability while minimizing time loss
Data Source
AI summary
Oscillator circuitry is disclosed. The oscillator circuitry comprises a free-running oscillator for generating pulses at a frequency, and a frequency adjustment circuit for adaptively adjusting the frequency of the free-running oscillator. The frequency adjustment circuit comprises a counter configured to count a number of pulses generated by the free-running oscillator and logic configured to compare the number of pulses with an expected number of pulses (corresponding to a target frequency) to determine a difference value and to adjust the frequency of the free-running oscillator in dependence on the difference value. The frequency adjustment circuit is configured, in response to receiving a synchronisation pulse, to trigger an update of the number of pulses to be compared.