Digitally Trimmed Clock Oscillator With RC Time-Base Servo Loop
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Solution Overview
Problem
Designing integrated circuits with high precision oscillators that do not require external components is challenging, especially for applications like CANFD, which demands a precision of ±0.4%, as existing solutions often rely on external crystals or advanced circuitry to achieve the required accuracy.
Innovation Solution
A high precision clock oscillator is developed using a digitally controlled oscillator with a low drift RC time base, which serves as a time reference for a servo-loop, allowing for digital trimming to adjust the oscillator frequency, eliminating the need for calibrating the RC time base and reducing propagation delay errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an external crystal or advanced circuitry is used to achieve high precision, then frequency precision is improved, but device complexity increases
Solution Approach 1:
The patent extracts the calibration function from the time base itself and applies it only to the oscillator frequency. By using a separate calibration mechanism that adjusts only the oscillator output frequency based on temperature, the system achieves high precision without requiring the entire time base to be complex or external.
Solution Approach 2:
The patent introduces an intermediary calibration mechanism that sits between the simple RC time base and the oscillator. This intermediary component (the frequency adjustment circuit) translates the simple time base signals into precisely calibrated oscillator frequencies, resolving the contradiction by adding only the necessary complexity where needed.
2Reliability
If calibration components are added to improve precision, then frequency stability is improved, but drift introduction increases
Solution Approach 1:
The patent applies calibration only where needed - specifically to the oscillator frequency output - rather than calibrating the entire time base system. This localized approach improves frequency stability at the critical output point while avoiding the drift issues that would arise from calibrating multiple components across the full temperature range.
Solution Approach 2:
The patent changes the calibration parameter from time base duration (which would require physical component adjustments) to oscillator frequency (which can be adjusted electronically). This parameter change allows for stable frequency calibration without introducing the mechanical drift problems associated with physical calibration components.
Data Source
Figure 1~2A
Figure 2B~3A
Figure 3B
AI summary
A clock oscillator includes a high speed oscillator generating a high speed clock signal and comprising a digital trimming function; a counter receiving said high speed clock signal at a clock input; a time base having a low drift and controlling said counter, wherein the counter generates a difference between a reference value and a counter value; and a digital integrator receiving said difference value and providing trimming data for said high speed oscillator.