Embedded RC Oscillator Tuning Using CTMU Frequency Measurement
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Solution Overview
Problem
Integrated circuit devices face challenges in maintaining precise clock frequency accuracy over time, temperature, and voltage changes due to internal self-contained RC oscillators, which can drift and require external crystal connections, limiting pin count availability.
Innovation Solution
A frequency tunable internal clock oscillator system using a Charge Time Measurement Unit (CTMU) with a capacitor and constant current source, coupled with an analog-to-digital converter and digital processor, automatically adjusts the clock frequency by sampling capacitor voltage and comparing it to a reference value, allowing for precise frequency maintenance within 0.25% accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an external crystal is used to control clock frequency accuracy, then frequency precision is improved, but the number of required package pins increases
Solution Approach 1:
The invention extracts the frequency determination function from external components (crystal) and implements it internally using an RC oscillator with on-chip frequency determining elements. This eliminates the need for external crystal connections and reduces package pin count while maintaining frequency control capability through internal calibration mechanisms.
Solution Approach 2:
The RC oscillator circuit is designed to serve multiple functions: frequency generation, frequency determination, and self-calibration. By integrating these functions into a single internal system, the invention eliminates the need for separate external crystal components and their associated package pins, while still achieving the required frequency accuracy for USB 2.0 compliance.
2Device complexity
If an internal self-contained RC oscillator is used to eliminate external pins, then package pin count is reduced, but frequency stability deteriorates due to drift from stress and environmental changes
Solution Approach 1:
The invention performs preliminary calibration of the RC oscillator frequency during manufacturing or initial operation. By pre-adjusting the frequency determining elements to achieve accurate frequency at calibration conditions, the system compensates for subsequent drift caused by package stress, soldering stress, temperature, and voltage changes, thereby maintaining frequency stability without external pins.
Solution Approach 2:
The system incorporates a feedback mechanism that monitors the RC oscillator frequency and automatically adjusts the frequency determining elements to compensate for drift. This closed-loop control counteracts the effects of package stress, temperature variations, and voltage changes, maintaining frequency stability within USB 2.0 specifications despite the absence of external crystal components.
3Device complexity
If internal frequency determining elements are used, then external crystal connections are eliminated, but frequency accuracy deteriorates over time due to drift from package and fabrication stress
Solution Approach 1:
The invention performs preliminary calibration of the RC oscillator frequency during manufacturing or initial operation. By pre-adjusting the frequency determining elements to achieve accurate frequency at calibration conditions, the system compensates for subsequent drift caused by package stress, soldering stress, temperature, and voltage changes, thereby maintaining frequency accuracy over time without external crystal connections.
Solution Approach 2:
The system dynamically adjusts the parameters of the frequency determining elements (such as resistor or capacitor values) to compensate for frequency drift over time. By changing these parameters in response to detected frequency deviations, the system maintains accurate frequency measurement and USB 2.0 compliance despite the absence of external crystal components and the presence of internal stress and environmental variations.
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
The system effectively maintains desired frequency accuracy by automatically adjusting the clock oscillator frequency, reducing the need for external crystals and minimizing pin usage, while compensating for temperature and voltage variations through stored tables.
Implementation Method 1
the CTMU to begin charging the known value capacitor with the known value constant current source upon detection of a first logic transition of the clock signal
Data Source
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AI summary
Precision measurement of a period(s) of an embedded clock oscillator using a charge time measurement unit (CTMU) maintains a desired frequency accuracy of the embedded clock oscillator over a range of time, temperature and operating condition changes. The CTMU determines the free running frequency of the embedded clock oscillator and provides very accurate frequency (period) information for confirmation that a desired frequency, e.g., within 0.25 percent of the desired frequency, is running or an indication of how much and which direction to adjustment the frequency of the clock oscillator to maintain the frequency precision desired. Automatic frequency adjustment of the embedded clock oscillator may be implemented so as to maintain the desired precision frequency thereof. Temperature and voltage compensation profiles for maintaining the accuracy of the CTMU may be stored in a table, e.g., nonvolatile memory, for a further improvement in absolute frequency accuracy of the embedded clock oscillator.