Digital Frequency Synthesizer Switching Between Frequency and Phase Lock
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Solution Overview
Problem
Previous digital frequency synthesizers with type-I loop dynamics fail to achieve absolute phase lock, resulting in prolonged settling times during the continuous phase-locking process.
Innovation Solution
A digital frequency synthesizer employing a digital filter with both phase and frequency paths, where the phase path is disabled during frequency acquisition and reset to achieve phase lock, transitioning from frequency-locked to phase-locked mode by adjusting the bandwidth and enabling the phase path after initial frequency lock is established.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the phase path is continuously enabled during frequency synthesis, then phase lock can be achieved, but the settling time becomes excessively long
Solution Approach 1:
The patent dynamically switches the phase path between enabled and disabled states based on the locking status. During frequency acquisition, the phase path is disabled to allow fast frequency settling. Once frequency lock is detected, the phase path is enabled to achieve phase lock. This dynamic control resolves the contradiction by adapting the phase path behavior to different operational phases.
Solution Approach 2:
The system employs periodic sampling of the frequency detector output to detect frequency lock condition. Based on these periodic samples, the control logic determines when to enable the phase path. This periodic detection mechanism allows the system to transition from frequency acquisition to phase locking at the appropriate moment, balancing speed and accuracy.
2Measurement precision
If a narrow bandwidth filter is used to achieve phase lock, then phase accuracy improves, but the frequency acquisition time increases
Solution Approach 1:
The bandwidth of the digital loop filter is dynamically adjusted based on operational phase. During frequency acquisition, a wide bandwidth is used to allow fast frequency tracking. After frequency lock is achieved, the bandwidth is narrowed to improve phase lock accuracy. This dynamic bandwidth adjustment resolves the contradiction between fast acquisition and accurate phase locking.
Solution Approach 2:
The system first achieves frequency lock using a wide bandwidth filter before transitioning to phase locking with a narrow bandwidth filter. This preliminary frequency acquisition phase prepares the system for the subsequent phase locking phase, ensuring that the oscillator is already close to the target frequency before precise phase alignment begins.
3Measurement precision
If the phase path is enabled during frequency acquisition, then phase information is available, but frequency lock stability deteriorates
Solution Approach 1:
The patent extracts the phase path from active operation during frequency acquisition by disabling it. This separation allows the frequency acquisition process to proceed independently without the destabilizing influence of phase path feedback. The phase path is then re-introduced only after frequency lock is established, when it can contribute to phase accuracy without compromising frequency stability.
Data Source
AI summary
A digital frequency synthesizer provides absolute phase lock and shorter settling time through the use of a digital filter with a phase and frequency path. Control logic control disables the frequency path during the frequency acquisition and sets a wide bandwidth. After frequency acquisition, a counter with digital phase information is reset using the input clock signal to bring the output phase closer to lock with the input signal and the control logic enables the phase path in the digital loop filter to achieve phase lock with a narrower bandwidth than the initial bandwidth.