Crystal Oscillator Start-Up with Adaptive Drive Level Control
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Solution Overview
Problem
Existing methods for starting up crystal oscillators require complex and power-consuming circuits to monitor and control bias current, leading to high power consumption and potential damage to the crystal due to overdriving, while failing to adapt drive levels to individual crystal properties effectively.
Innovation Solution
A method using a microprocessor-controlled oscillator circuit with a look-up table to set and adjust a programmable bias current or load capacitance, ensuring a stable start-up and operation by automatically adapting drive levels based on crystal properties, reducing power consumption and preventing overdriving.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high bias current is used at start-up to ensure reliable oscillator startup, then the startup reliability is improved, but the crystal may be damaged by overdriving and power consumption increases
Solution Approach 1:
The bias current is made dynamically adjustable through a programmable current source that can set different current levels at different startup stages. The microprocessor controls the bias current to start at a high level for reliable startup, then automatically reduces it to a lower operational level, transforming the static current into a dynamic parameter that adapts to startup requirements without causing permanent damage.
Solution Approach 2:
The invention changes the bias current parameter over time during the startup sequence. Initially, a high bias current is applied to ensure reliable oscillator startup, then the microprocessor automatically reduces the bias current to a lower level for normal operation. This parameter change resolves the contradiction by allowing high current only temporarily during startup while protecting the crystal from sustained overdriving.
2Measurement precision
If a complex feedback loop with rectifying and A/D-converting is used to monitor amplitude and control bias current, then the drive level control precision is improved, but the device complexity and power consumption increase
Solution Approach 1:
The invention extracts and removes the complex feedback loop components (rectifiers, A/D converters, D/A converters) from the system. Instead of using these complex circuits to monitor and control the bias current, the microprocessor directly controls the programmable current source based on predetermined startup sequences, eliminating the need for expensive high-quality components and complex signal processing circuits while maintaining adequate control precision.
Solution Approach 2:
The invention replaces the analog feedback loop mechanism with a digital control approach. The microprocessor implements the control logic in the digital domain, using software-programmable current sources instead of analog rectifying and converting circuits. This substitution simplifies the hardware while maintaining the ability to precisely control the drive level through digital parameter adjustment.
3Measurement precision
If a complex feedback loop with signal processing is used to control bias current, then the drive level control is improved, but the power consumption increases
Solution Approach 1:
The invention removes the power-consuming signal processing components (rectifiers, A/D converters, D/A converters) from the feedback loop. The microprocessor controls the bias current directly through a programmable current source without requiring these intermediate signal processing stages, thereby significantly reducing power consumption while maintaining adequate drive level control for startup and operation.
4Reliability
If the drive level is set to a fixed high value at start-up, then the startup reliability is improved, but the crystal may be damaged by sustained overdriving
Solution Approach 1:
The bias current is made dynamically adjustable through a programmable current source that can set different current levels at different startup stages. The microprocessor controls the bias current to start at a high level for reliable startup, then automatically reduces it to a lower operational level, transforming the static current into a dynamic parameter that adapts to startup requirements without causing permanent damage.
Solution Approach 2:
The invention implements a two-stage periodic control sequence: first, a high bias current is applied during the startup phase to ensure reliable oscillator initialization, then the microprocessor transitions to a second phase with a reduced bias current for normal operation. This periodic action pattern ensures the crystal receives high drive levels only temporarily during startup while protecting it from sustained overdriving that would reduce its lifespan.
Data Source
Figure 1
Figure 2~3
Figure 3A~3B
AI summary
The method concerns the reliable start-up of a crystal oscillator where the drive levels the crystal is subjected to are kept low in order to avoid over-driving the crystal. After applying a start-up value (12) of a parameter controlling the drive level where the drive level associated with the start-up value is rather high such that reliable start-up is ensured the parameter is modified step-wise so as to reduce the drive level until the crystal oscillator ceases to operate regularly (17, 18). To assess whether this is the case, the frequency of the crystal oscillator is compared with the frequency of an auxiliary oscillator. A safety margin is added to the parameter and the result stored in a non-volatile memory as an operating value (19). The crystal oscillator is then restarted with the start-up value (13) and after a delay the operating value is applied (14). The start-up value can be determined using an initial value for the parameter which is associated with a moderate drive level and where necessary modifying the parameter step-wise, increasing the drive level until the oscillator starts up. The start-up value so determined is also stored in the non-volatile memory. In subsequent start-ups the stored start-up value and operating value can be applied immediately.