Digital RC Oscillator Tuning for 0.1% On-Chip Frequency Accuracy
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Solution Overview
Problem
Internal oscillators lack the precision to achieve frequencies with accuracy beyond 0.5%, as trimming on-chip components like resistors or capacitors to high accuracy is impractical, and existing high-precision solutions require external components or complex trimming processes, making it difficult to tune oscillators to specific frequencies with high accuracy.
Innovation Solution
A Frequency Tuning Module (FTM) uses a precision analog RC module with a digitally controllable oscillator, where the clock division ratio 'trims' the RC time constant, allowing for precise frequency tuning by adjusting the number of clock periods, thereby attenuating errors and achieving 0.1% accuracy without physical trimming of components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If physical trimming of on-chip resistors or capacitors is used to achieve high precision, then frequency accuracy can be improved, but manufacturing complexity and cost increase significantly
Solution Approach 1:
The patent replaces physical/mechanical trimming of on-chip components with a digital correction approach. A frequency correction module digitally adjusts the output frequency of the oscillator based on calibration data, eliminating the need for laser trimming or physical adjustment of resistors and capacitors. This substitution of mechanical trimming with digital correction resolves the contradiction by achieving high frequency accuracy without increasing manufacturing complexity.
2Measurement precision
If external precision components are used to achieve high precision, then frequency accuracy can be improved, but device integration and cost increase
Solution Approach 1:
The patent merges the frequency correction functionality directly into the on-chip oscillator circuit by integrating a frequency correction module that uses digital signal processing. This integration combines the oscillator and correction functions into a single unified circuit, eliminating the need for separate external precision components while maintaining high frequency accuracy. The merging resolves the contradiction by achieving both integration and precision.
3Measurement precision
If multiple oscillators are trimmed separately to achieve high precision, then frequency accuracy of each oscillator can be improved, but test time and cost increase
Solution Approach 1:
The patent implements a self-calibration mechanism where the frequency correction module automatically adjusts oscillator frequencies based on pre-stored calibration data in a lookup table. During testing, the system automatically selects and applies the appropriate correction values without requiring manual intervention for each oscillator. This self-service approach maintains high frequency accuracy while dramatically improving test efficiency by eliminating repetitive manual trimming operations.
4Measurement precision
If an oscillator is tuned to one frequency with high precision, then frequency accuracy at that frequency can be improved, but the ability to retune to other frequencies with similar accuracy decreases
Solution Approach 1:
The patent implements a dynamic frequency correction system where the frequency correction module can be reconfigured for different operating frequencies. The system stores multiple sets of calibration data corresponding to different frequency points and dynamically switches between them based on the desired operating frequency. This dynamic adaptability allows the oscillator to maintain high frequency accuracy across multiple frequency points, resolving the contradiction between precision at a single frequency and versatility across multiple frequencies.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables oscillators to achieve 0.1% or better accuracy, reduces the impact of non-idealities, and allows for flexible, digital reconfiguration of multiple oscillators on a chip, making the solution simple, inexpensive, and practical.
Implementation Method 1
an RC delay element having a delay period equal to a predetermined time period
Implementation Method 2
an RC delay element comprising a digital buffer, a resistor, a capacitor and a comparator
Data Source
AI summary
A system, method and apparatus for tuning an internal oscillator to a desired frequency F1 is shown and uses an RC delay element that comprises a resistor, a capacitor and a comparator. The method includes receiving a clock signal from an oscillator to be tuned, triggering charging of the RC delay element, and N clock cycles after triggering the charging, the method determines whether the charge on the precision RC delay element is higher than or lower than a reference voltage. Correction to the clock frequency is based on the results.