RC Oscillator Offset Compensation for Accurate CAN Transceiver Clocks
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Solution Overview
Problem
CAN transceivers require a highly accurate time base with low current consumption and space-saving design to meet stringent frequency and temperature tolerance requirements, while quartz oscillators and ceramic resonators are cost- and space-prohibitive.
Innovation Solution
An oscillator with a timing element and comparator that uses switchable capacitance for offset compensation, allowing for low current consumption and accurate frequency generation, suitable for CAN transceivers in partial networking applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a quartz oscillator or ceramic resonator is used as a time base, then frequency accuracy and stability are improved, but cost and space requirements increase making it prohibitive for CAN transceiver applications
Solution Approach 1:
The patent replaces the mechanical quartz oscillator or ceramic resonator with an electronic RC oscillator circuit implemented in integrated circuit form. This substitution eliminates the need for mechanical resonating elements while achieving comparable frequency accuracy through electronic timing components (resistors and capacitors) and a comparator-based oscillation mechanism, thereby reducing space and cost.
2Measurement precision
If a quartz oscillator or ceramic resonator is used as a time base, then frequency accuracy and stability are improved, but cost increases making it prohibitive for CAN transceiver applications
Solution Approach 1:
The patent replaces the mechanical quartz oscillator or ceramic resonator with an electronic RC oscillator circuit implemented in integrated circuit form. This substitution eliminates the need for mechanical resonating elements while achieving comparable frequency accuracy through electronic timing components (resistors and capacitors) and a comparator-based oscillation mechanism, thereby reducing space and cost.
Solution Approach 2:
The oscillator circuit is designed as a universal integrated circuit that can be directly integrated into CAN transceiver chips, serving multiple functions including time base generation, frequency regulation, and temperature compensation. This multi-functionality reduces the need for separate components, lowering overall manufacturing cost and simplifying production.
3Measurement precision
If conventional oscillators are used to meet frequency accuracy requirements, then frequency tolerance is improved, but current consumption increases beyond the 150 μA limit
Solution Approach 1:
The patent employs a comparator-based oscillation mechanism that operates in periodic cycles, charging a timing capacitor through a resistor and detecting the threshold voltage periodically. This periodic action allows the oscillator to achieve accurate frequency control through controlled charging/discharging cycles rather than continuous high-current operation, thereby reducing average current consumption to below 150 μA while maintaining frequency tolerance requirements.
Solution Approach 2:
The patent optimizes the parameters of the RC circuit (resistance and capacitance values) and the comparator threshold to achieve the desired frequency accuracy with minimal current consumption. By carefully selecting and adjusting these parameters, the oscillator maintains frequency tolerance within specified limits while operating at ultra-low current levels suitable for energy-constrained CAN transceiver applications.
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 solution provides a low current consumption of <150 μA and frequency tolerance of up to +/−1.0% in the temperature range from −40° C. to 175° C., while being compact enough for use in CAN transceivers, supporting data transfer rates of up to 500 kbps in CAN-HS and 1 Mbps in CAN-FD systems.
Implementation Method 1
a frequency-determining capacitance for determining the frequency of the clock frequency
Implementation Method 2
a comparator, the comparator being configured to detect a threshold voltage to which the frequency-determining capacitance is to be charged
Data Source
AI summary
An oscillator, a transmission/reception device for a bus system, and a method for generating a clock frequency with the oscillator are indicated. The oscillator serves to generate a clock frequency and includes a timing element that has a frequency-determining capacitance for determining the frequency of the clock frequency, and a comparator, the comparator being configured to detect a threshold voltage to which the frequency-determining capacitance is to be charged, and the comparator having a switchable capacitance for offset compensation.