PLL Startup Voltage Control for Fast VCO Frequency Lock
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Solution Overview
Problem
Phase-locked loops (PLLs) face challenges in startup time and stability, particularly when a reference signal is lost, as existing methods are limited by design parameters and performance characteristics, leading to instability and disruption in output frequency.
Innovation Solution
A method is introduced where a startup voltage source provides a reference voltage to a voltage-controlled oscillator (VCO) in PLLs, incrementally increasing it until a convergence criterion is met, allowing the feedback loop to open and then close, enabling faster startup and maintaining frequency lock even when the reference signal is lost by recalling and applying a stored voltage value.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional PLL startup methods are used, then the PLL can achieve frequency lock, but the startup time is excessive and stability is poor when reference signal is lost
Solution Approach 1:
The patent applies preliminary action by pre-charging the capacitor to an initial voltage level before PLL startup. This initial voltage is set based on expected operating conditions, allowing the VCO to start at or near the correct frequency. When the reference signal is lost, the system recalls the stored voltage value and re-applies it to maintain frequency lock, avoiding the need to wait for slow conventional re-lock procedures.
Solution Approach 2:
The patent changes the voltage parameter dynamically by storing the voltage value during normal operation and recalling it during reference signal loss. The system monitors the control voltage applied to the VCO and stores this value in memory. When reference signal is lost, the stored voltage is re-applied to maintain the VCO frequency, effectively changing the system's response from slow re-lock to immediate frequency maintenance.
2Productivity
If the reference voltage is increased to improve startup speed, then startup time decreases, but frequency accuracy and convergence become difficult to control
Solution Approach 1:
The system performs preliminary action by pre-charging the capacitor to an initial voltage that corresponds to the expected operating frequency. This allows the VCO to start immediately at the correct frequency without requiring slow incremental voltage increases, thus achieving both fast startup and high frequency accuracy simultaneously.
Solution Approach 2:
The patent implements feedback by monitoring the control voltage applied to the VCO during normal operation and storing this voltage value in memory. When the reference signal is lost, the system uses this stored feedback voltage to maintain the VCO frequency, ensuring frequency accuracy is preserved while enabling rapid response. The feedback mechanism allows the system to learn the correct operating voltage and reuse it when needed.
Data Source
AI summary
A method of startup for a phase-locked loop (PLL) can include, at initiation of the PLL, providing a reference voltage from a startup voltage source to an input of a voltage controlled oscillator (VCO) in the PLL, wherein the reference voltage is set to a predetermined minimum voltage. The reference voltage can be stepwise increased from the predetermined minimum voltage. A frequency of a reference signal input to the PLL can be compared with a frequency of a feedback signal originating from an output of the VCO of the PLL to determine a frequency differential as the reference voltage increases. A determination can be made as to whether a convergence criterion is met according to the frequency differential. While the convergence criterion is not met, the reference voltage can be increased. When the convergence criterion is met, the reference voltage provided by the startup voltage source can be replaced with a voltage generated by an operational voltage source.