Head Gimbal Assembly Height Measurement With Charge-to-Voltage Conversion

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Solution Overview

Problem

Conventional methods for determining head gimbal assembly (HGA) height in hard disk drives are sensitive to process, voltage, and temperature variations, making it difficult to accurately measure small capacitance changes due to the sensitivity of relaxation oscillators and comparator jitter.

Innovation Solution

A discrete-time, switched-capacitor charge-to-voltage converter is used to measure changes in capacitance by converting the stored charge to voltage, which is then compared to a threshold voltage or digitized via an ADC, reducing sensitivity to timing and environmental variations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If conventional relaxation oscillator methods are used to measure capacitance changes, then the measurement system is simple, but the measurement precision deteriorates due to sensitivity to PVT variations and comparator jitter

Engineering Contradiction:

Improvecapacitance change measurement accuracyVSAvoidmeasurement circuit complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent replaces the conventional relaxation oscillator-based capacitance measurement system with a charge-to-voltage converter system. This substitution eliminates the mechanical/oscillator-based timing mechanisms that are sensitive to PVT variations, replacing them with a direct charge conversion approach that is inherently more stable and precise for measuring small capacitance changes in HGA height determination.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the measurement parameter from direct capacitance measurement using oscillators to voltage measurement after charge conversion. By converting the capacitance measurement problem into a voltage measurement problem through the charge-to-voltage converter, the system achieves higher precision because voltage measurements are less susceptible to PVT variations and comparator jitter than oscillator-based capacitance measurements.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If conventional capacitance measurement methods are used, then the device structure is simple, but reliability deteriorates due to sensitivity to process, voltage, and temperature variations

Engineering Contradiction:

Improvemeasurement stability under PVT variationsVSAvoidcharge-to-voltage converter circuit complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent replaces the oscillator-based measurement system with a charge-to-voltage converter system, which substitutes the unreliable timing/oscillation mechanism with a direct charge conversion mechanism. This substitution improves reliability by eliminating the sensitivity to PVT variations that plagues oscillator-based systems, as the charge conversion process is inherently more stable under varying process, voltage, and temperature conditions.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Measurement precision

If small capacitance changes are measured directly, then the measurement process is fast, but measurement precision deteriorates due to the small magnitude of the signal

Engineering Contradiction:

Improvesmall capacitance change detection accuracyVSAvoidmeasurement time

Core Design Contradiction:

Measurement precisionVSLoss of time

Solution Approach 1:

The patent changes the measurement approach by converting small capacitance changes into voltage changes through the charge-to-voltage converter. This parameter transformation amplifies the effective measurement signal, allowing small capacitance changes to be detected with high precision without requiring extended measurement times, as the voltage output provides a directly measurable and amplified representation of the capacitance variation.

Inventive Principle:

Principle #35Parameter changes

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 provides more accurate and robust HGA height determination by amplifying small capacitance changes, reducing head wear, and minimizing the impact of PVT variations, while also reducing power consumption.

Implementation Method 1

a first capacitor (215) coupled to the first switch, wherein the first capacitor is formed by at least part of a head gimbal assembly and a storage media

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 2

A discrete-time, switched-capacitor charge-to-voltage converter is used to measure changes in capacitance by converting the stored charge to voltage

Methodology Applied

Scientific EffectCharge-to-voltage conversion:

Data Source

PatentUS12451158B2Head gimbal assembly height determination with charge-to-voltage converter

Publication Date: 2025.10.21 AVAGO TECHNOLOGIES INTERNATIONAL SALES PTE LTD

AI summary

A circuit for determining head gimbal assembly (HGA) height is provided. The circuit includes a first switch configured to be controlled by a first clock signal, an amplifier, and a first capacitor coupled to the first switch, wherein the first capacitor is formed by at least part of a head gimbal assembly and a storage media. The circuit further includes a second capacitor coupled to an input of the amplifier, and an output of the amplifier, wherein the second capacitor is configured to store a charge from the first capacitor over one or more cycles of the first clock signal. The amplifier is configured to generate an output voltage based, at least in part, on a change in the capacitance of the first capacitor over the one or more cycles of the first clock signal.