MEMS Microphone Open-Loop LFRO Correction Using Digital Transfer Functions

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Solution Overview

Problem

MEMS devices, particularly piezoelectric MEMS microphones, face significant variability in their low frequency roll-off (LFRO) points due to manufacturing process variations, leading to inconsistent performance and high yield loss when specific frequency responses are required.

Innovation Solution

An open loop correction circuit is employed to receive an input signal representing the analog signal from a MEMS transducer and apply a transfer function to correct the LFRO point digitally, moving the pole from a first frequency to a desired second frequency, using digital circuitry to improve accuracy and reduce silicon area.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If analog correction methods are used to adjust LFRO point, then manufacturing yield can be improved, but device complexity and power consumption increase

Engineering Contradiction:

Improvemanufacturing yieldVSAvoiddevice complexity

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The patent replaces analog correction circuits with digital correction implemented through software algorithms running on the ADC processor. The transfer function correction is performed in the digital domain after ADC conversion, eliminating the need for complex analog components and circuits while achieving the same LFRO adjustment effect.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the correction approach from analog domain to digital domain by applying a transfer function in the digital signal processing stage. This parameter change allows the same correction functionality to be achieved with simpler hardware while providing greater flexibility through software configuration.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If analog correction circuits are used to correct LFRO point, then performance consistency can be improved, but power consumption increases

Engineering Contradiction:

Improveperformance consistencyVSAvoidpower consumption

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent substitutes power-hungry analog correction circuits with digital correction algorithms executed on the ADC's integrated processor. The digital domain correction maintains performance consistency through precise software-based transfer function application while consuming significantly less power than analog circuitry.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Area of stationary object

If digital correction is applied after ADC, then silicon area is reduced, but measurement precision requirements increase

Engineering Contradiction:

Improvesilicon areaVSAvoidmeasurement precision

Core Design Contradiction:

Area of stationary objectVSMeasurement precision

Solution Approach 1:

The patent introduces the ADC as an intermediary component that converts the analog transducer output to digital form before correction. This intermediary conversion enables subsequent digital transfer function application, reducing silicon area compared to analog correction while maintaining precision through the ADC's inherent conversion accuracy and digital processing capabilities.

Inventive Principle:

Principle #24Intermediary (Mediator)

4Reliability

If manufacturing process variations are reduced to achieve consistent LFRO, then performance consistency improves, but manufacturing cost increases

Engineering Contradiction:

Improveperformance consistencyVSAvoidmanufacturing cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent applies preliminary digital correction through a transfer function that compensates for manufacturing variations. Instead of requiring precise manufacturing control, the system pre-calculates and applies correction factors in the digital domain, effectively correcting LFRO deviations without requiring costly manufacturing process improvements.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS20250358574A1Transducer system with open loop correction of low frequency roll off point

Publication Date: 2025.11.20 QUALCOMM INC

AI summary

In some aspects, a system may comprise a transducer configured to generate an analog signal as a function of an incident signal and an open loop correction circuit configured to control or correct a low frequency roll off (LFRO) point, also known as a three decibel (dB) point, of the analog signal generated by the transducer. For example, in some aspects, the open loop correction circuit may receive an input signal that represents the analog signal, wherein the input signal is associated with a first frequency response with a pole at a first frequency, and the open loop correction circuit may apply a transfer function to the input signal to generate an output signal, wherein the output signal is associated with a second frequency response in which the pole is moved to a second frequency. Numerous other aspects are described.