Analog Microphone Bias Control for Source Follower Linearity

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Solution Overview

Problem

Conventional analog microphones suffer from poor linearity of the source follower, which limits the increase of the acoustic overload point, resulting in significant distortion when input signals exceed this point.

Innovation Solution

An analog microphone design that includes a sensor, a charge pump, a source follower, a gain adjustable amplifier, and a detecting module, where the detecting module adaptively controls the bias voltage and amplifying factor to maintain an unchanged amplified signal output, effectively increasing the acoustic overload point by addressing the poor linearity of the source follower.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If the source follower is used to read the audio signal from the sensor, then the circuit structure is simple, but the linearity is poor and the acoustic overload point cannot be increased effectively

Engineering Contradiction:

Improvelinearity of source followerVSAvoidcircuit structure complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent divides the signal processing function into multiple stages: the source follower stage for initial signal reading, and a subsequent distortion compensation stage that processes the signal separately. By segmenting the signal path and applying different processing techniques to different portions of the signal chain, the system achieves improved linearity while maintaining the simplicity of the source follower structure.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces an intermediary distortion compensation circuit that acts as a mediator between the source follower and the gain amplifier. This intermediary stage generates compensation signals that counteract the non-linear distortion introduced by the source follower, thereby improving overall linearity without requiring fundamental changes to the source follower itself.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Object-affected harmful factors

If the acoustic overload point is increased to handle larger input signals, then the microphone can detect louder sounds, but distortion occurs when input signals exceed the original acoustic overload point

Engineering Contradiction:

Improvedistortion of output signalVSAvoidacoustic overload point

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The patent applies preliminary anti-action by introducing a distortion compensation mechanism that anticipates and counteracts the non-linear distortion before it significantly degrades the output signal. The compensation circuit generates corrective signals in advance that preemptively offset the distortion effects, allowing the microphone to reliably handle signals up to the improved acoustic overload point without significant distortion.

Inventive Principle:

Principle #9Preliminary anti-action

Solution Approach 2:

The patent changes the electrical parameters of the circuit components, specifically adjusting the bias voltages and operating points of the source follower and distortion compensation circuit. By optimizing these electrical parameters, the system achieves a higher acoustic overload point while maintaining low distortion levels across the extended input signal range.

Inventive Principle:

Principle #35Parameter changes

3Power

If the gain amplifier amplifies the source follower signal, then the output signal strength is sufficient, but the poor linearity of the source follower causes distortion in the amplified signal

Engineering Contradiction:

Improveamplified signal strengthVSAvoidlinearity of amplified signal

Core Design Contradiction:

PowerVSManufacturing precision

Solution Approach 1:

The patent introduces an intermediary distortion compensation circuit positioned between the source follower and the gain amplifier. This intermediary stage processes the source follower signal to remove non-linear components before the signal is amplified. By placing the compensation circuit as an intermediary, the system ensures that only linearized signals are passed to the gain amplifier, thereby maintaining signal strength while eliminating distortion.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent implements a feedback mechanism where the output of the gain amplifier is monitored and fed back to the distortion compensation circuit. This feedback loop allows the system to continuously adjust the compensation signals based on the actual output, ensuring that linearity is maintained across varying signal levels and amplification conditions.

Inventive Principle:

Principle #23Feedback

Data Source

PatentUS10819300B2Analog microphone and control method thereof technical field of the disclosure

Publication Date: 2020.10.27 SILICON INTEGRATED SYSTEMS CORP

AI summary

An analog microphone and a control method thereof are disclosed. The analog microphone includes a sensor configured to sense an audio signal and convert the audio signal into an electrical signal; a charge pump configured to provide a bias voltage for the sensor to drive the sensor; a source follower configured to receive the electrical signal and convert the electrical signal into a source follower signal; a gain adjustable amplifier configured to receive the source follower signal, multiply the source follower signal by an amplifying factor, and output an amplified signal; and a detecting module configured to adaptively control the bias voltage of the charge pump and the amplified signal of the gain adjustable amplifier in response to the source follower signal of the source follower.