Overtone Crystal Oscillator Calibration for Reliable Low-Current Startup
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Solution Overview
Problem
Conventional overtone crystal oscillators face challenges in maintaining minimal current drain and reliable startup due to process-induced variations in manufacturing, which affect loop gain and frequency response, leading to potential operational failures.
Innovation Solution
An automatic calibration system that adjusts the closed-loop gain and phase response of the overtone crystal oscillator by programmable resistance and supply voltage, allowing sequential adaptation from low to high gain states to ensure startup at the desired overtone frequency, even with variations in semiconductor process and crystal loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional startup circuits increase oscillator loop gain to ensure startup, then startup reliability is improved, but current drain increases
Solution Approach 1:
The patent applies dynamics by making the loop gain adjustable rather than fixed. A gain control circuit dynamically adjusts the loop gain of the oscillator based on detected fundamental mode oscillation, allowing the system to have high gain when needed for startup and low gain during normal operation, thus resolving the contradiction between startup reliability and current drain
Solution Approach 2:
The patent implements feedback through a detection circuit that monitors for fundamental mode oscillation and feeds this information back to the gain control circuit. This closed-loop feedback mechanism enables automatic adjustment of loop gain to maintain startup reliability while minimizing current consumption during normal overtone operation
2Ease of manufacture
If process-induced variations occur during manufacturing, then manufacturing ease is improved, but oscillator operational reliability deteriorates
Solution Approach 1:
The patent applies parameter changes by making the loop gain a variable parameter that can be adjusted to compensate for process-induced variations. The gain control circuit changes the loop gain parameter based on detected oscillation conditions, allowing the oscillator to maintain reliable operation despite manufacturing variations in component values and crystal characteristics
Solution Approach 2:
The system transitions from a static, fixed-gain design to a dynamic, adjustable-gain design. This allows the oscillator to adapt to process variations automatically, ensuring reliable operation across different manufacturing batches without requiring tight manufacturing tolerances
3Reliability
If loop gain is increased to compensate for crystal loss variance, then startup reliability is improved, but current drain increases
Solution Approach 1:
The patent makes the loop gain dynamic rather than fixed, allowing it to be increased temporarily when crystal loss is high and startup is difficult, then reduced when startup is achieved. This dynamic adjustment ensures startup reliability across varying crystal loss conditions while minimizing current drain during normal operation
Solution Approach 2:
The detection circuit provides feedback about oscillation status to the gain control circuit, enabling automatic compensation for crystal loss variance. When fundamental mode oscillation is detected (indicating potential startup issues), the feedback mechanism triggers gain increase to ensure reliable startup, then reduces gain once startup is achieved
Data Source
AI summary
An overtone crystal oscillator automatic calibration system including an overtone crystal oscillator with multiple programmable resistors and multiple amplifiers with supply voltage inputs and a calibration system. The calibration system adjusts the programmable resistors and the supply voltage inputs and detects oscillation of the overtone crystal oscillator. The calibration system adjusts the programmable resistors and the supply voltage input for each of multiple sequential steps to adjust the frequency bandwidth, such as from a higher bandwidth and lower gain to a lower bandwidth at higher gain. For example, each resistance level is tested for each of multiple supply voltage levels. The range of resistances and voltages is designed to ensure oscillation at a selected overtone frequency while avoiding oscillation at a fundamental frequency of the oscillator crystal. Oscillation may be detected by a counter which counts to a predetermined count value indicating successful oscillation.