Adaptive PLL Filter Bandwidth for HAMR Read Channel Phase Errors
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In heat-assisted magnetic recording (HAMR) technology, phase errors due to laser instability, such as mode hopping, cause abrupt changes in the phase of recorded waveforms, leading to timing-induced errors during data reading, which conventional decoding methods struggle to recover, resulting in unrecoverable error bits and slowed drive performance.
Innovation Solution
A phase-locked loop (PLL) filter system that dynamically adjusts its bandwidth by selecting phase and frequency coefficients from a look-up table based on the magnitude of phase error signals, allowing for continuous and adaptive compensation of phase disturbances, including those caused by mode hopping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a conventional fixed bandwidth PLL filter is used, then the circuit complexity is low, but the drive cannot adapt to abrupt phase changes caused by mode hopping, resulting in timing-induced errors
Solution Approach 1:
The PLL filter transitions from a fixed bandwidth design to a dynamic bandwidth design where the bandwidth can be adjusted in real-time. The system includes a bandwidth selector that switches between multiple filter coefficients stored in memory, allowing the filter bandwidth to adapt to different operating conditions including mode hopping events.
Solution Approach 2:
The invention changes the bandwidth parameter of the PLL filter dynamically by selecting from multiple pre-stored filter coefficients. When mode hopping is detected or anticipated, the system switches to a larger bandwidth coefficient to accommodate the abrupt phase changes, thereby maintaining tracking accuracy without requiring complex real-time calculations.
2Reliability
If the PLL filter bandwidth is increased to handle mode hopping, then the ability to compensate for phase disturbances improves, but noise rejection capability deteriorates
Solution Approach 1:
The system dynamically adjusts the PLL filter bandwidth based on operating conditions. During normal operation, a smaller bandwidth coefficient is used for optimal noise rejection. When mode hopping is detected or anticipated, the system switches to a larger bandwidth coefficient to accommodate abrupt phase changes, thereby maintaining tracking accuracy without continuously exposing the system to noise penalties.
Solution Approach 2:
The system periodically evaluates whether mode hopping conditions exist and switches between different bandwidth coefficients accordingly. This periodic adjustment allows the system to maintain optimal performance by using larger bandwidth only when necessary for phase compensation, rather than maintaining a continuously large bandwidth that would degrade noise rejection.
Data Source
AI summary
A phase-locked loop (PLL) filter of a read channel includes a filter portion having an input coupled to delay circuitry having an output. The input of the filter portion is configured to receive a phase error signal. A look-up table is coupled to the filter portion. The look-up table comprises phase coefficients and frequency coefficients associated with a plurality of phase error magnitudes. The look-up table is configured to provide one or both of a selected phase coefficient and a selected frequency coefficient based on a magnitude of the phase error signal. The PLL filter is configured to adjust a bandwidth of the filter portion using one or both of the selected phase coefficient and the selected frequency coefficient. A phase signal indicative of estimated phase disturbance is produced at the output of the delay circuitry.