Oscillator Frequency Tuning Using Trimmed Comparator Feedback
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Solution Overview
Problem
Conventional internal oscillators suffer from significant frequency accuracy degradation due to comparator delay and offset variations caused by process, voltage, and temperature changes, making it difficult to achieve high accuracy without the cost of external crystal oscillators.
Innovation Solution
The system employs calibration logic to monitor the output of a trimmed calibration circuit, controlling the on and off times of an oscillator to correct frequency errors, utilizing a dual-oscillator configuration where one oscillator controls the on time and the other controls the off time, with the clock period being more independent of comparator offset, thus maintaining accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If an internal oscillator is used to reduce cost, then cost is reduced, but frequency accuracy deteriorates
Solution Approach 1:
The patent implements a feedback mechanism where the oscillator output is fed back through a delay element to a comparator, which adjusts the oscillator control signal based on the phase relationship between the original and delayed signals. This closed-loop feedback system automatically compensates for frequency deviations caused by comparator offset and delay variations, achieving high frequency accuracy without requiring expensive external crystal oscillators.
2Measurement precision
If comparator delay and offset are corrected, then frequency accuracy is improved, but the other parameter (delay or offset) deteriorates
Solution Approach 1:
The patent converts the harmful effects of comparator offset and delay into a useful signal. By intentionally introducing a delay element and comparing the delayed oscillator output with the original output, the system generates an error signal that is proportional to frequency deviations. This error signal is then used to adjust the oscillator, transforming the comparator's inherent imperfections into the basis for automatic frequency correction.
3Device complexity
If a single oscillator is used, then device complexity is reduced, but frequency tuning capability is limited
Solution Approach 1:
The patent makes a single oscillator system perform multiple functions through the feedback loop. The same oscillator generates the clock signal, and its output is simultaneously used as the reference signal for the comparator after being delayed. The feedback mechanism provides both frequency measurement and automatic tuning capabilities within a single oscillator configuration, eliminating the need for separate tuning circuits or multiple oscillators.
Data Source
AI summary
A system for tuning an oscillator frequency. The system includes a trimmed calibration circuit comprising a comparator and trimmed delay element and calibration logic. The calibration logic is configured to receive an output of the comparator and control an on time and an off time of an oscillator based on the output of the comparator.