Transconductance Current Loop for Hard Disk Drive Voice Coil Motor
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Solution Overview
Problem
Current control circuit devices for Hard Disk Drives have limited bandwidth due to local loops and poles of amplifiers, which restrict the performance of voice coil motor current loops, necessitating a solution that reduces hardware components and eliminates local feedback to enhance bandwidth.
Innovation Solution
A transconductance current loop is implemented without local compensation, closing downstream of a first transconductance amplifier associated with the sensing resistance, using two transconductance amplifiers and a resistive divider to detect and control current flow in the voice coil motor, eliminating the need for external resistive and capacitive components and local feedback loops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If local feedback loops and multiple amplifiers are used in the current control circuit, then the circuit provides stable current control, but the bandwidth is limited due to amplifier poles and local compensation requirements
Solution Approach 1:
The patent extracts and removes the local feedback loops and local compensation networks from the circuit. By eliminating these local loops that were creating bandwidth limitations through their poles and zeros, the design achieves broader bandwidth while maintaining overall current control stability through the global feedback architecture
Solution Approach 2:
The patent segments the control circuit into distinct functional blocks with clear separation of concerns. The current sense amplifier, output amplifier, and feedback network are divided into independent stages, each optimized for specific functions without the bandwidth-limiting interactions of local compensation loops
2Measurement precision
If multiple amplifiers and external components are used to achieve accurate current detection and control, then the control precision is improved, but the device complexity and hardware requirements increase
Solution Approach 1:
The patent merges the current sensing function and amplification function into a single integrated current sense amplifier stage. This consolidation maintains accurate current detection capability while reducing the total number of discrete components and simplifying the overall circuit architecture
Solution Approach 2:
The output amplifier is designed to perform multiple functions: it provides current amplification, drives the voice coil motor, and participates in the global feedback loop. This multi-functionality eliminates the need for separate dedicated components for each function, reducing hardware complexity while maintaining control precision
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
This configuration increases the bandwidth of the current loop, eliminates frequency limitations, and simplifies the circuit by removing local loops and amplifiers, resulting in improved performance and reduced hardware requirements for Hard Disk Drive applications.
Implementation Method 1
a sensing resistance, connected in series with the motor and at least a driving driver for a relative coil of the motor
Implementation Method 2
A transconductance current loop is implemented without local compensation, closing downstream of a first transconductance amplifier associated with the sensing resistance
Implementation Method 3
The application of a controlled current on the coil causes an interaction between the permanent magnets and the coil itself so as to drive the motor according to well known Lorentz relations
Data Source
AI summary
A reduced hardware control circuit device includes a current loop for broad band Hard Disk Drive applications. The current loop detects the value of the current flowing on the coils of a voice coil electric motor incorporated in the Hard Disk Drive. A sensing resistance is connected in series with the motor and at least a driving driver for a relative motor coil. Advantageously the current loop is a transconductance loop with a first transconductance amplifier associated with the sensing resistance. A second transconductance amplifier is provided for fixing the current value to be applied to the motor. The circuit device advantageously is deprived of a local compensation in correspondence with the first transconductance amplifier.