Relaxation Oscillator Temperature Compensation Using Opposite TC Resistors
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Solution Overview
Problem
Relaxation oscillators formed on semiconductor chips experience significant variations in oscillation frequency due to temperature changes, making them unstable frequency sources, and existing solutions have been insufficient in addressing first-order frequency deviations.
Innovation Solution
A relaxation oscillator design that incorporates a reference voltage source, two current source circuits with resistors having opposite first-order temperature coefficients, and variable capacitors with capacitance ratios adjusted to cancel out first-order frequency deviations, ensuring the product of current ratios and temperature coefficients have the same absolute value and opposite signs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a relaxation oscillator is formed on a semiconductor chip using a variable resistor, then the oscillator can be integrated into semiconductor devices, but the oscillation frequency largely varies due to the temperature coefficient of the variable resistor
Solution Approach 1:
The patent changes the temperature coefficient parameter of the resistor by switching between a first resistor (with first-order temperature coefficient) and a second resistor (with second-order temperature coefficient) based on temperature detection. This allows the oscillator to maintain stable frequency across temperature ranges by adapting the resistor characteristics to compensate for temperature effects.
Solution Approach 2:
The patent implements a feedback mechanism where a temperature detection circuit monitors the temperature and controls a switch to select between different resistors based on temperature ranges. This feedback loop enables the oscillator to automatically adjust its resistance characteristics to maintain frequency stability despite temperature variations.
2Device complexity
If resistors with large first-order temperature coefficients are used in the relaxation oscillator, then the circuit can be simplified, but the oscillation frequency varies significantly with temperature changes
Solution Approach 1:
The patent segments the temperature compensation function by dividing the temperature range into multiple ranges and assigning different resistors to different ranges. The first resistor handles lower temperature ranges while the second resistor handles higher temperature ranges, allowing each resistor to be optimized for its specific range rather than requiring a single complex resistor design.
Solution Approach 2:
The patent uses a composite approach by combining multiple resistors with different temperature coefficient characteristics (first-order and second-order) to create an effective composite resistance system. This composite structure allows the oscillator to achieve temperature stability that neither resistor could provide alone.
3Reliability
If existing temperature compensation methods are applied to relaxation oscillators, then some frequency stability can be achieved, but first-order frequency deviations remain insufficiently addressed
Solution Approach 1:
The patent changes the dominant temperature coefficient parameter from first-order to second-order by switching resistors based on temperature range. This parameter change enables effective compensation of first-order frequency deviations that previous methods could not address, achieving superior frequency stability across the entire operating temperature range.
Data Source
AI summary
Provided is a relaxation oscillator having an extremely small temperature deviation in oscillation frequency. A first current (I1) generated by a reference voltage source and a first resistor having a positive first-order temperature coefficient is supplied to a first variable capacitor (C1) for oscillation, and a second current (I2) generated by a reference voltage source and a second resistor having a negative first-order temperature coefficient is supplied to a second variable capacitor (C2) for oscillation. A product of a value of a ratio of a first current to a second current and a value of a ratio of a first-order temperature coefficient of the second resistor to a first-order temperature coefficient of the first resistor, and a value of a ratio of a capacitance of the first variable capacitor to a capacitance of the second variable capacitor have the same absolute value and opposite signs.