Oscillator Calibration Using LC Reference for Lifetime Frequency Accuracy
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Solution Overview
Problem
Existing oscillator circuits, particularly relaxation oscillators, face challenges in maintaining frequency accuracy over their lifetime due to PVT-L&M variations, leading to instability and inaccuracy, while more stable LC oscillators consume higher power and occupy more space, and external clock sources increase cost and complexity.
Innovation Solution
A calibration system that uses a more frequency stable LC oscillator to generate a sampled value, which is stored and used to tune a relaxation oscillator, allowing it to maintain frequency accuracy without an external clock, adjusting the tune value as the oscillator ages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If a relaxation oscillator is used, then power consumption is reduced and space requirements are minimized, but frequency accuracy and stability deteriorate over time due to PVT-L&M variations
Solution Approach 1:
The system performs preliminary calibration during manufacturing by comparing the relaxation oscillator output with a precise external clock signal, storing the difference as a trim value in non-volatile memory. This preliminary action compensates for frequency deviations before the product is deployed, allowing the low-power relaxation oscillator to maintain accuracy without continuous external reference.
Solution Approach 2:
The calibration system uses the relaxation oscillator itself to generate calibration data by comparing its output with an external reference during manufacturing. The stored trim value enables the oscillator to self-correct its frequency deviations autonomously during operation, eliminating the need for continuous external clock signals while maintaining frequency accuracy.
2Measurement precision
If an external clock signal is used for calibration, then frequency accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The system performs frequency calibration during the manufacturing process using an external clock signal, storing the measured trim value in non-volatile memory. After calibration, the external clock is removed and the system operates autonomously using only the stored trim value, thereby achieving high frequency accuracy without requiring permanent external clock infrastructure.
Solution Approach 2:
The external clock signal is extracted from the operational system and used only during the initial calibration phase. The calibration data is then stored internally, allowing the system to achieve frequency accuracy without the ongoing presence or complexity of external clock infrastructure.
3Measurement precision
If calibration is performed during manufacturing, then frequency accuracy is improved, but the oscillator drifts over lifetime due to aging and environmental variations
Solution Approach 1:
The system autonomously recalibrates itself during operation by periodically comparing the relaxation oscillator output with the stored trim value and adjusting the frequency accordingly. This self-service mechanism compensates for drift caused by aging, temperature changes, and voltage variations throughout the oscillator's lifetime, maintaining frequency accuracy without external intervention.
Solution Approach 2:
The system implements a feedback loop that continuously monitors the relaxation oscillator frequency and adjusts it based on the stored trim value and real-time measurements. This feedback mechanism counteracts drift caused by PVT-L&M variations and aging, maintaining frequency accuracy over the oscillator's operational lifetime.
Data Source
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AI summary
An oscillator system for an integrated circuit includes a first oscillator circuit, a second oscillator circuit, and calibration system. During a sampling routine, the calibration system is used to determine a sampled value based on a comparison of the output of the second oscillator and an external clock signal. The sampled value is stored in a memory. During a calibration routine, the calibration system determines a comparison value based on a comparison of the output of the second oscillator circuit and the output of the first oscillator circuit. The calibration circuit compares the comparison value with the sampled value to generate a tuning value to tune the frequency of the first oscillator circuit.