Microphone ADC Input Compensation for Common-Mode Mismatch
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Solution Overview
Problem
The existing coupling configurations between microphones and analog-to-digital converters (ADCs) are inflexible, leading to common mode and differential mode mismatches that result in poor ADC performance, such as clipping and saturation, limiting the use of different microphone topologies with electronic devices.
Innovation Solution
A method and apparatus that determine the coupling configuration of a microphone coupled to differential input nodes of an ADC by analyzing digital common mode and differential mode data, generating a control signal to compensate for common mode and differential mode mismatches using a digital-to-analog converter, thereby adjusting the ADC's operation to match the microphone topology.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If AC-coupled configuration with capacitors is used to interface microphone and ADC, then DC blocking is achieved, but device size and cost increase due to capacitor requirements
Solution Approach 1:
The patent extracts the DC blocking function from external capacitors and implements it within the ADC circuitry itself through differential input nodes and internal signal processing, eliminating the need for external coupling capacitors and reducing device size
Solution Approach 2:
The ADC is designed with universal input circuitry that can handle both AC-coupled and DC-coupled microphone configurations through the same differential input nodes, allowing the system to perform multiple coupling functions without requiring separate hardware paths
2Reliability
If ADC is designed for specific microphone configuration, then optimal performance is achieved, but adaptability to different microphone topologies is reduced
Solution Approach 1:
The patent implements dynamic configuration detection and adaptation where the system automatically detects the microphone coupling type (AC or DC, differential or pseudo-differential) and adjusts the ADC input circuitry configuration in real-time to match the connected microphone topology
Solution Approach 2:
The ADC incorporates universal differential input nodes that can interface with multiple microphone topologies (fully-differential, pseudo-differential, AC-coupled, DC-coupled) through a single unified interface design, eliminating the need for multiple specialized ADC designs
3Volume of moving object
If DC-coupled configuration is used to eliminate capacitors, then device size and cost are reduced, but common mode and differential mode mismatches occur
Solution Approach 1:
The patent implements feedback mechanisms where the ADC monitors the actual voltage levels at the differential input nodes and adjusts its internal processing to compensate for detected common mode and differential mode mismatches, ensuring accurate signal conversion despite DC-coupling variations
Solution Approach 2:
The system dynamically adjusts processing parameters such as gain, offset, and differential scaling based on the detected microphone configuration and measured input node characteristics, optimizing signal accuracy for each specific DC-coupled microphone topology
4Adaptability or versatility
If multiple coupling configurations are supported, then microphone compatibility is improved, but ADC circuitry complexity increases
Solution Approach 1:
The patent segments the ADC input circuitry into independent functional blocks (differential input nodes, common mode rejection circuitry, gain control stages) that can be independently configured and controlled, allowing complex multi-configuration support to be achieved through modular control rather than complex hardware
Data Source
Figure 1A~1D
Figure 1E~1G
Figure 2
AI summary
An analog-to-digital converter (ADC) may include capability to sense and/or compensate for undesired effects when receiving input from a microphone. For example, a sense node may be provided between differential inputs, and that sense node separated from the differential inputs by two or more switches. The sense node may allow for a measurement of an average voltage of the differential inputs. The average voltage may be obtained activating the switches to sample the sampling capacitors coupled to the differential inputs. That average voltage may be used as common mode (CM) data. A controller may receive the CM data, along with differential mode (DM) data, and use the CM and DM data to determine undesired effects, such as DC or AC mismatch at the microphone interface. The controller may then generate a signal for applying compensation to the differential inputs to reduce or eliminate the undesired effects.