Bridged T-Coil Termination Network for HDD Write Circuit Bandwidth
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Solution Overview
Problem
Conventional impedance matching techniques, such as resistance or shunt inductance, are ineffective at high write currents and data rates in hard disk drive write circuitry, leading to reflections and distortions that limit bandwidth.
Innovation Solution
A bridged T-coil termination network is used for impedance matching between write current and overshoot current drivers and the transmission line, comprising mutually-coupled inductors and a bridge capacitor, which reduces loading capacitance and enhances impedance matching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional resistance or shunt inductance is used for impedance matching, then impedance matching is achieved, but bandwidth is limited at high write currents and data rates
Solution Approach 1:
The patent changes the impedance matching approach from conventional resistance or shunt inductance to a bridged T-coil network with specific inductance values (L1, L2) and capacitance (C1, C2), optimizing the network parameters to achieve both impedance matching and extended bandwidth at high write currents and data rates
Solution Approach 2:
The bridged T-coil network acts as an intermediary circuit between the write current driver and the transmission line, providing impedance transformation and matching while extending the bandwidth beyond what conventional matching techniques can achieve
2Device complexity
If conventional impedance matching is used, then circuit simplicity is maintained, but reflections and distortions occur that limit data rate
Solution Approach 1:
The patent introduces a bridged T-coil network with optimized inductance and capacitance parameters that reduces loading capacitance and minimizes reflections, enabling higher data rates while maintaining reasonable circuit complexity through systematic parameter selection
3Productivity
If impedance matching is optimized for high currents, then bandwidth increases, but circuit complexity increases
Solution Approach 1:
The impedance matching function is segmented into a bridged T-coil network with distinct inductive (L1, L2) and capacitive (C1, C2) elements, allowing independent optimization of each component to achieve bandwidth extension while managing overall circuit complexity
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 bridged T-coil arrangement extends the bandwidth of hard disk drive write circuitry, improving data rate and reducing peak variance, DC settling, and peak-to-peak jitter, with a 2.7 times better 3 dB data rate extension compared to termination resistor-based solutions.
Implementation Method 1
A bridged T-coil termination network is used for impedance matching between write current and overshoot current drivers and the transmission line, comprising mutually-coupled inductors and a bridge capacitor
Implementation Method 2
comprising mutually-coupled inductors and a bridge capacitor, which reduces loading capacitance and enhances impedance matching
Data Source
AI summary
Write apparatus for a disk drive includes a write head, write current circuitry connected to the write head for generating a steady-state write current, overshoot current circuitry connected to the write head for generating write current overshoot pulses, and a T-coil termination network between (a) the write current circuitry and the overshoot current circuitry, and (b) a first node connected to a first input of a transmission line together with the write head. The T-coil termination network may include a first inductor connected to the first node, a second inductor coupled with the first inductor at a second node, and a first termination resistor between the first inductor and a common voltage. An output of the overshoot current circuitry may be connected to the first node, and an output of the write current circuitry may be connected to the second node.