P-Type FET Microphone Input Stage Noise Attenuation
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Solution Overview
Problem
Existing microphone assemblies with P-type field effect transistors amplify noise when the diaphragm and back-plate are coupled to the gate input relative to ground, leading to unwanted disturbances in the audio signal.
Innovation Solution
The diaphragm and back-plate of a condenser transducer element are operatively connected between the source and gate inputs of a P-type field effect transistor, effectively attenuating electronic noise from the power supply line, reducing noise amplification and improving power supply rejection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the diaphragm and back-plate are coupled to the gate input of the P-type field effect transistor relative to ground, then the electrical interface is established, but noise applied at the source input is amplified causing unwanted disturbances in the audio signal
Solution Approach 1:
The patent inverts the conventional coupling arrangement by connecting the diaphragm to the source input and the back-plate to the gate input of the P-type field effect transistor, rather than coupling both to the gate input relative to ground. This inversion changes the reference configuration, allowing the source input to be connected to a DC voltage supply node instead of ground, thereby preventing noise amplification while maintaining proper electrical interface functionality
Solution Approach 2:
The patent introduces a DC voltage supply node as an intermediary between the source input and ground. This intermediary allows the source input to be referenced to a stable DC voltage level rather than directly to ground, which acts as a mediator that prevents noise from being amplified while still providing a proper reference for the electrical interface
2Ease of operation
If the diaphragm and back-plate are coupled to the gate input, then the transducer element is connected to the preamplifier, but power supply noise is not rejected effectively
Solution Approach 1:
The patent inverts the conventional connection topology by swapping the coupling points: the diaphragm is connected to the source input and the back-plate to the gate input, rather than both being coupled to the gate input. This inverted configuration inherently provides better power supply noise rejection because the source input is referenced to a DC voltage supply node, isolating the signal path from power supply fluctuations
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 configuration minimizes electronic input-referred noise and reduces light-induced noise in silicon microphone assemblies by 20-30 dB, enhancing the quality of the audio signal.
Implementation Method 1
The displaceable diaphragm and the back-plate are arranged to form a capacitor in combination
Implementation Method 2
A preamplifier circuit has an input stage, the input stage comprising a P-type field effect transistor. The displaceable diaphragm and the back-plate are operatively connected between a source input and a gate input of the P-type field effect transistor
Data Source
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AI summary
A microphone assembly is provided that includes a condenser transducer element having a displaceable diaphragm and a back-plate. The displaceable diaphragm and the back-plate are arranged to form a capacitor in combination. A preamplifier circuit has an input stage, the input stage comprising a P-type field effect transistor. The displaceable diaphragm and the back-plate are operatively connected between a source input and a gate input of the P-type field effect transistor.