Microphone DC Bias Circuit Using Deep Trench Isolation

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Solution Overview

Problem

Microphone assemblies with low mechanical compliance face limitations in sensitivity and signal-to-noise ratio due to the constraints of breakdown voltages of transistors within the DC bias circuit, which restrict the increase of DC bias voltage beyond a certain level, hindering further miniaturization and performance enhancement.

Innovation Solution

The implementation of a DC bias circuit with deep trench isolation (DTI) technology, allowing for the creation of transistors with increased breakdown voltage, enabling the generation of voltages above 50 volts while maintaining a small footprint, thereby enhancing sensitivity and signal-to-noise ratios in microphone assemblies.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If DC bias voltage is increased to improve sensitivity and signal-to-noise ratio, then microphone performance is improved, but transistor breakdown voltage limits prevent further voltage increase

Engineering Contradiction:

Improvesensitivity and signal-to-noise ratioVSAvoidtransistor breakdown voltage limit

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent changes the electrical parameters of the transistor by implementing deep trench isolation, which modifies the breakdown voltage characteristic from a limiting factor to an enhanced parameter, enabling operation at higher DC bias voltages above 50 volts while maintaining reliability

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The deep trench isolation structure acts as an intermediary element between the transistor and the high voltage environment, providing electrical insulation and field control that mediates the interaction between high voltage and the sensitive transistor components, allowing higher bias voltages without breakdown

Inventive Principle:

Principle #24Intermediary (Mediator)

2Measurement precision

If DC bias voltage is increased to enhance sensitivity, then microphone assembly performance is improved, but available space within the microphone assembly is constrained

Engineering Contradiction:

ImprovesensitivityVSAvoidavailable space within microphone assembly

Core Design Contradiction:

Measurement precisionVSArea of stationary object

Solution Approach 1:

The patent transitions from planar transistor design to three-dimensional deep trench isolation structures, utilizing the vertical dimension to achieve higher breakdown voltages without increasing the horizontal footprint, thereby maintaining compact microphone assembly dimensions while enabling higher bias voltages for improved sensitivity

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Data Source

PatentUS11553283B2Microphone assembly having a direct current bias circuit with deep trench isolation

Publication Date: 2023.01.10 KNOWLES ELECTRONICS LLC

AI summary

The disclosure describes devices and methods of providing a DC bias voltage in a microphone assembly. Particularly, one implementation of such a device may be implemented on an integrated circuit that includes a direct current (DC) bias circuit. The DC bias circuit may be coupled to a transducer and configured to supply a DC bias signal to the transducer. The DC bias circuit includes a multi-stage charge pump and a low pass filter (LUFF) circuit. The multi-stage charge pump includes transistors that are fabricated with deep trench isolation (DTI).