MEMS Microphone Assembly Using Current-Input ADC for Lower Noise
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Solution Overview
Problem
Portable communication devices face challenges in reducing noise and improving sound quality due to limited overload margins and distortion caused by saturation of active amplification elements, particularly in voltage-based amplifier systems, which restricts the power consumption and physical size of microphones.
Innovation Solution
A microphone assembly utilizing a transconductance amplifier that converts sound into an amplified current signal, which is then sampled and quantized by a current-input analog-to-digital converter (I-ADC), avoiding voltage-to-current conversion and allowing for increased signal-to-noise ratio (SNR) without compromising power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a voltage-based amplifier is used in the microphone assembly, then the device can achieve signal amplification, but the overload margin is limited and distortion occurs due to saturation of active amplification elements
Solution Approach 1:
The patent changes the fundamental operating parameter from voltage-based amplification to current-based amplification. The transconductance amplifier converts the voltage output of the MEMS transducer directly to a current signal, bypassing the voltage amplification stage that causes saturation. This parameter change eliminates the overload distortion problem while maintaining amplification capability.
2Object-affected harmful factors
If noise reduction measures are implemented in compact devices, then sound quality improves to some extent, but power consumption and physical size constraints prevent further noise reduction
Solution Approach 1:
The patent replaces the conventional voltage-based amplification mechanism with a current-based transconductance amplification mechanism. This substitution fundamentally changes the signal processing approach, eliminating the need for high-gain voltage amplification that introduces noise. The current-based system achieves superior noise performance without increasing power consumption.
3Volume of moving object
If the microphone assembly is made compact for portable devices, then the device size is reduced, but the overload margin decreases leading to distorted signals
Solution Approach 1:
The patent changes the signal representation parameter from voltage to current throughout the processing chain. The transconductance amplifier and current-input ADC work together to maintain the signal in current form, which has higher impedance and is less susceptible to loading effects and distortion in compact configurations. This enables compact design without sacrificing signal fidelity.
4Measurement precision
If a voltage-input ADC is used, then the system can convert voltage signals to digital, but noise is increased due to the need for voltage-to-current conversion
Solution Approach 1:
The patent inverts the conventional approach by using a current-input ADC instead of a voltage-input ADC. Rather than converting voltage to current at the ADC input, the system maintains the signal in current form throughout and directly converts current to digital. This inversion eliminates the noisy voltage-to-current conversion stage and achieves superior signal-to-noise ratio.
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
This solution significantly reduces noise and enhances the signal-to-noise ratio, allowing for improved sound quality and increased overload margins without increasing power consumption or physical size, as demonstrated by the comparison with voltage-input analog-to-digital converter (V-ADC) implementations.
Implementation Method 1
a transconductance amplifier including an input node connected to the transducer output for receipt of the microphone signal voltage. The transconductance amplifier is configured to generate an amplified current signal representative of the microphone signal voltage in accordance with a predetermined transconductance (gm) of the transconductance amplifier
Data Source
AI summary
A microphone assembly comprising: a housing including a base, a cover, and a sound port; a MEMS transducer element disposed in the housing, the transducer element configured to convert sound into a microphone signal voltage at a transducer output; and a processing circuit. The processing circuit comprising a transconductance amplifier comprising an input node connected to the transducer output for receipt of the microphone signal voltage, the transconductance amplifier being configured to generate an amplified current signal representative of the microphone signal voltage in accordance with a predetermined transconductance of the transconductance amplifier; and an analog-to-digital converter comprising an input node connected to receive the amplified current signal, said analog-to-digital converter being configured to sample and quantize the amplified current signal to generate a corresponding digital microphone signal.