RC Oscillator Offset Compensation for Low-Power CAN Time Bases
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Solution Overview
Problem
The CAN bus system requires a high-precision time base with low current consumption for transceivers in partial network operation, but existing solutions like crystal or ceramic resonators are cost- and space-prohibitive, and current noise cancellation methods are inefficient.
Innovation Solution
A low-power oscillator design with switchable capacitance and a comparator that uses MOS transistors to detect threshold voltage, allowing for precise clock frequency generation with low current consumption, suitable for CAN transceivers in extreme temperature ranges and high-speed data transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a quartz crystal or ceramic resonator is used as the time base, then frequency accuracy and stability are improved, but cost and space requirements increase making the solution infeasible
Solution Approach 1:
The patent replaces expensive quartz crystals or ceramic resonators with a low-cost RC oscillator circuit implementation. The oscillator uses simple resistors and capacitors that can be integrated into the ASIC, eliminating the need for expensive external crystal components while achieving the required frequency accuracy through careful circuit design and calibration.
Solution Approach 2:
The patent substitutes the mechanical resonance principle of quartz crystals with an electrical RC oscillation principle. The oscillator circuit generates the required clock frequency through resistive and capacitive time constants rather than mechanical vibration, enabling integration into standard ASIC processes without requiring specialized crystal mounting and connection infrastructure.
2Measurement precision
If the CAN transceiver is equipped with a highly accurate time base, then frequency and time tolerance are improved, but current consumption increases beyond the 150 μA limit
Solution Approach 1:
The patent implements a low-power RC oscillator that operates periodically to generate the required clock frequency. The oscillator circuit is designed to consume minimal current by using efficient switching mechanisms and optimized component values, achieving the required frequency tolerance of ±1% to ±1.6% while maintaining current consumption below the 150 μA limit in receive mode.
3Reliability
If noise cancellation methods are applied to the oscillator, then signal quality is improved, but device complexity and power consumption increase
Solution Approach 1:
The patent extracts and eliminates the need for complex noise cancellation circuits by designing an inherently low-noise RC oscillator. The oscillator circuit is designed to minimize noise generation at the source through careful component selection and circuit topology, rather than requiring additional active noise cancellation stages that would increase complexity and power consumption.
Data Source
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AI summary
What is disclosed is: an oscillator (150), a transmission/reception device (12) for a bus system (1) and a method for generating a clock frequency using the oscillator (150). The oscillator (150) is used for generating a clock frequency (f) and comprises a timing element (151), which has a frequency-determining capacitance (1513) for determining the frequency of the clock frequency (f) and a comparator (1514), wherein the comparator (1514) is configured to identify a threshold value voltage (UTH) up to which the frequency-determining capacitance (1513) is to be charged, and wherein the comparator (1514) has a switchable capacitance (15147) for offset compensation.