Variable Capacitance Oscillation Circuit for Linear Frequency Tuning
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Solution Overview
Problem
Existing oscillation circuits, such as temperature-compensated crystal oscillators, face challenges in securing a range where the oscillation frequency linearly changes with respect to a control voltage, especially when dealing with wide temperature ranges, as the sensitivity of capacitance value change for the control voltage may be reduced, leading to non-linear frequency changes.
Innovation Solution
The oscillation circuit incorporates a variable capacitance circuit with multiple capacitive elements having different inflection point voltages and potential difference-capacitance value characteristics, allowing for controlled capacitance values based on varying reference voltages and control voltages, ensuring a wider range of linear frequency deviation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If capacitance values of variable capacitive elements at inflection point voltages are made the same, then device complexity is reduced, but the range in which oscillation frequency linearly changes with respect to control voltage is insufficient
Solution Approach 1:
The patent applies local quality by making each variable capacitive element have different capacitance values at their respective inflection point voltages. Specifically, the first variable capacitive element has capacitance C1 at inflection point voltage V1, while the second variable capacitive element has capacitance C2 at inflection point voltage V2, where C1 ≠ C2. This local differentiation ensures that the combined capacitance maintains appropriate sensitivity across the entire control voltage range, securing a wider linear oscillation frequency change range without excessive complexity.
2Adaptability or versatility
If a wide temperature range is covered, then adaptability is improved, but the sensitivity of capacitance value change for control voltage is reduced
Solution Approach 1:
The patent segments the temperature compensation function across multiple variable capacitive elements, each optimized for different voltage ranges. The first variable capacitive element operates effectively at lower control voltages with inflection point at V1, while the second element operates at higher control voltages with inflection point at V2. This segmentation allows the combined capacitance to maintain high sensitivity across the entire wide temperature range, as each element contributes its maximum sensitivity in its optimal operating region.
Solution Approach 2:
The patent implements dynamics by having the dominant capacitance contribution shift between the first and second variable capacitive elements as the control voltage changes. When control voltage is below V1, the first element provides the primary capacitance variation. When control voltage is between V1 and V2, both elements contribute. When control voltage exceeds V2, the second element becomes dominant. This dynamic redistribution of capacitance contributions maintains optimal sensitivity throughout the wide temperature range.
Data Source
AI summary
An oscillation circuit includes an amplification circuit that causes a resonator to oscillate, and a variable capacitance circuit whose capacitance value is controlled on the basis of a control voltage. The variable capacitance circuit includes a first variable capacitive element in which an inflection point voltage in a change characteristic of a capacitance value for the control voltage is a first voltage, and a second variable capacitive element in which an inflection point voltage in a change characteristic of a capacitance value for the control voltage is a second voltage which is different from the first voltage. A capacitance value of the first variable capacitive element when the control voltage is the first voltage is different from a capacitance value of the second variable capacitive element when the control voltage is the second voltage.