Microphone Amplifier Circuit Using Source Follower to Cut THD
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Solution Overview
Problem
Current microphone amplifier circuits suffer from poor total harmonic distortion (THD) performance due to the capacitive loading effect of the parasitic capacitor Cgd, which degrades the sound output quality in electronic devices.
Innovation Solution
The amplifier circuit incorporates a source follower configuration with transistors and constant current sources to maintain a constant voltage across the parasitic capacitor Cgd, effectively canceling or minimizing the capacitive loading effect, thereby improving THD performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional amplifier circuit is used, then the circuit structure is simple, but the THD performance is poor due to capacitive loading effect
Solution Approach 1:
The patent introduces a source follower circuit as an intermediary between the amplifier and the load. This source follower acts as a buffer that isolates the amplifier from the capacitive loading effect of the parasitic capacitor Cgd, thereby improving THD performance without significantly complicating the overall circuit structure.
Solution Approach 2:
The patent extracts the capacitive loading effect caused by parasitic capacitor Cgd from the main amplification path by using a source follower configuration. The source follower separates the amplification function from the capacitive load, allowing the main amplifier to operate without the degrading effects of capacitive loading.
2Object-affected harmful factors
If the parasitic capacitor Cgd is present, then the transistor function is maintained, but capacitive loading effect degrades sound output quality
Solution Approach 1:
The source follower circuit serves as an intermediary that blocks the harmful capacitive loading effect from propagating back to the amplifier. It maintains the necessary transistor function while preventing the parasitic capacitor Cgd from degrading sound output quality through its buffering action.
Solution Approach 2:
The patent converts the harmful capacitive loading effect into a benefit by using the parasitic capacitor Cgd in conjunction with the source follower to create a stable operating point. The source follower transforms what would be a source of distortion into a component that helps stabilize the amplifier's operation.
Data Source
AI summary
An amplifier circuit for a microphone, a microphone circuit and an electronic device are provided. The amplifier circuit includes a first transistor having a gate serving as an input terminal of the amplifier circuit, a source serving as an output terminal of the amplifier circuit and a drain connected to ground, a first constant current source having an input terminal connected to a power supply and an output terminal connected to the source of the first transistor, and a source follower including at least a second transistor, having a drain connected to the power supply, a gate connected to the source of the first transistor and a source connected to the drain of the first transistor.