Programmable Writer Overdrive for Faster HDD Head Current Response
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Solution Overview
Problem
As writer head current in HDD applications increases, reducing interconnect impedance to accommodate launch voltage leads to reduced bandwidth and slower head current response, necessitating an improved write driver solution.
Innovation Solution
The implementation of a programmable write driver circuit with programmable current sources and sinks, variable resistances, and H-bridge configuration to control current flow direction and amplitude, enhancing head current response through overdrive currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If interconnect impedance is reduced to accommodate launch voltage, then writer head current increases, but bandwidth is reduced and head current response becomes slower
Solution Approach 1:
The patent applies preliminary action by pre-charging the interconnect line to a voltage level above the steady-state operating voltage before data transitions occur. This pre-charge prepares the line to source higher current during transitions, enabling faster head current response without requiring lower impedance interconnects. The pre-charged line can quickly discharge through the write driver during a transition, delivering the necessary launch voltage and current to the write head faster than a traditionally charged line could.
Solution Approach 2:
The patent changes the voltage parameter of the interconnect line by maintaining it at an elevated pre-charged voltage level rather than the conventional steady-state voltage. This parameter change allows the interconnect to deliver higher instantaneous current during transitions while maintaining higher impedance, thereby improving both the writer head current and the response speed simultaneously by exploiting the voltage-headroom created by pre-charging.
2Productivity
If writer head current increases to improve magnetic saturation, then data rate capability improves, but interconnect bandwidth is reduced
Solution Approach 1:
The pre-charging mechanism performs preliminary action by storing energy in the interconnect line's capacitance at an elevated voltage level before data transitions. This预先 stored energy is rapidly discharged during transitions to deliver high current to the write head, enabling high data rates without requiring sustained high current through the interconnect, thereby preserving interconnect bandwidth while achieving the necessary peak current for improved magnetic saturation and data rate capability.
Solution Approach 2:
The patent employs periodic action by applying pre-charge signals at specific intervals before anticipated data transitions occur. This periodic pre-charging synchronizes with the data rate requirements, delivering bursts of high current only when needed for transitions, thereby achieving high data rate performance while maintaining lower average current through the interconnect and preserving overall bandwidth.
Data Source
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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.