PLL Free-Running Voltage Correction for Faster Lock Acquisition
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Solution Overview
Problem
Phase locked loop (PLL) circuits face a conflict between extending the frequency pull-in range and reducing lockup time, as increased locking speed degrades steady-state characteristics due to mismatches in control voltages and individual differences in voltage control oscillators, leading to longer lockup times.
Innovation Solution
A phase locked loop circuit configuration that includes a phase comparator, loop filter, controller, free-running voltage generator, measurement circuit, and storage circuit to calculate and apply a correction value to the free-running voltage signal, ensuring the voltage control oscillator operates efficiently across different frequencies and temperatures, thereby reducing lockup time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the frequency pull-in range is extended and locking speed is increased, then lockup time is reduced, but the noise band of the loop is extended and steady-state characteristics are degraded
Solution Approach 1:
The invention applies preliminary action by pre-calculating and storing correction values for free-running voltages at different frequency points before operation. When a frequency change is detected, the corresponding correction value is immediately retrieved and applied, avoiding real-time calculation delays and ensuring both fast locking and stable steady-state performance.
Solution Approach 2:
The invention changes parameters by adjusting the free-running voltage based on pre-stored correction values corresponding to different frequency division ratios. This allows the PLL to optimize its locking characteristics for each frequency point while maintaining stable steady-state operation, resolving the contradiction between fast locking and stable characteristics.
2Speed
If a fixed control voltage for free-running frequency control is changed to reduce lockup time, then locking speed improves, but mismatches with actual locked state control voltage increase due to individual differences, leading to longer lockup time
Solution Approach 1:
The invention changes parameters by storing multiple correction values corresponding to different frequency points and individual oscillator characteristics. This allows the system to select the most accurate correction value for the current operating conditions, improving both locking speed and voltage match accuracy simultaneously.
Solution Approach 2:
The invention applies feedback by using the measured control voltage from the actually locked state to determine the appropriate correction value. This feedback mechanism ensures that the free-running voltage is adjusted based on actual oscillator behavior, compensating for individual differences and achieving both fast locking and accurate voltage matching.
Data Source
AI summary
A phase locked loop circuit includes a phase comparator that compares phases of a reference signal through a first frequency divider and a local signal through a second frequency divider to output a phase comparison signal; a loop filter that smooths the phase comparison signal to output the control voltage signal; a controller that sets frequency division ratios of the first and the second frequency dividers; a free-running voltage generator that generates a free-running voltage signal of the voltage control oscillator; a measurement circuit that measures a voltage of the control voltage signal; a storage circuit that stores therein the voltage of the control voltage signal; and a low-pass filter that transmits, to the voltage control oscillator, a corrected free-running voltage signal based on a free-running voltage correction value calculated by the free-running voltage generator based on the control voltage signal before the frequency division ratios are changed.