Programmable Write Driver Overdrive for Faster Head Current Response
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Solution Overview
Problem
The reduction in interconnect impedance to accommodate higher write driver currents in HDDs leads to reduced bandwidth and slower head current response, necessitating an improved write driver design.
Innovation Solution
A programmable write driver system incorporating a pre-amp with symmetrical half-circuits and programmable current sources/sinks, along with variable resistances, to regulate and overdrive current flow, enhancing head current response through adjustable overdrive, steady state, and overshoot currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If interconnect impedance is reduced to accommodate higher write driver currents, then current capacity is improved, but bandwidth is reduced and head current response becomes slower
Solution Approach 1:
The patent applies preliminary action by introducing an overdrive current pulse before the steady-state current. This overdrive pulse pre-charges the interconnect and write head, reducing the effective rise time. The overdrive current is applied for a limited duration (e.g., 1-2 nanoseconds) before transitioning to steady-state current, thereby improving the effective response speed without requiring permanently high current levels that would demand even lower impedance.
Solution Approach 2:
The patent uses periodic action through oscillating or pulsed overdrive currents that alternate between high and low states. This periodic current application allows the system to achieve high current levels only when needed for rapid transitions, while maintaining lower average current levels. The periodic nature enables bandwidth preservation while still achieving fast response when data transitions occur.
2Strength
If higher write driver currents are used, then magnetic saturation is improved, but interconnect bandwidth is reduced
Solution Approach 1:
The overdrive current pulse performs preliminary action by rapidly charging the interconnect capacitance and establishing the magnetic field in the write head before the main data current arrives. This preliminary magnetic field establishment ensures that when the steady-state current follows, the magnetic saturation is already partially achieved, reducing the required steady-state current level and preserving interconnect bandwidth for subsequent data transitions.
Solution Approach 2:
The patent implements dynamics by making the write driver current time-varying rather than static. The current profile transitions from an high-amplitude overdrive pulse to a lower steady-state level, adapting the current magnitude to the specific needs of each phase of the write operation. This dynamic current control achieves magnetic saturation during the critical transition phase while maintaining bandwidth during steady-state operation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution improves the rise time of head current, allowing for higher data rates and improved magnetic saturation on the disk surface by overcoming electrical bandwidth limitations.
Implementation Method 1
Hard disc drive (HDD) write drivers are electronic circuits responsible for converting digital data into current during the recording of data. Magnetic signals resulting from the current are written onto disc platters by the write head during the data recording.
Data Source
AI summary
An apparatus including a current source. The current source divides a current from a voltage supply into current streams in response to converting a voltage from a voltage supply into a plurality of current streams. The current source modulates a current streams with signals to convert the current streams into first and second current streams. The current source combines the first and second current streams into a single current stream and supplies the single current stream to a load in a flow direction.