Bias Resistor Circuit for Electret Microphone Linearity
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Solution Overview
Problem
Electret condenser microphones (ECMs) in semiconductor devices face issues with high output impedance and low output frequency, leading to biased signal distortion and increased total harmonic distortion due to the change in bias resistance values when large signal amplitudes are inputted, which deteriorates the amplification circuit's linearity.
Innovation Solution
A semiconductor device with a resistor circuit comprising first and second transistors, a first resistor, and a capacitor, where the drain of the first transistor is connected to the input terminal, and the gate of the second transistor is connected to the other end of the first resistor, with a voltage supply circuit connected to the other end of the first resistor and the gate of the second transistor, allowing for variable resistance adjustment through the current source, improving linearity and reducing distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a high resistance bias resistor is formed using a MOSFET drain-source resistance, then the bias resistance value can be achieved to match manufacturing steps, but the bias voltage changes when large signal amplitudes are inputted, causing deterioration of distortion characteristics
Solution Approach 1:
The single MOSFET bias resistor is segmented into multiple MOSFETs connected in parallel. This segmentation allows the bias resistance to be maintained while reducing the impact of signal-induced voltage changes on the overall bias characteristics, thereby improving distortion performance without sacrificing manufacturing precision
Solution Approach 2:
The invention changes the operational parameters of the MOSFETs by applying specific gate voltages (VGS1, VGS2) that are controlled to remain below threshold voltages. This parameter control ensures that the MOSFETs operate in a region where their drain-source resistance remains stable even when large signal amplitudes are applied, resolving the contradiction between maintaining bias resistance and preventing distortion
2Stability of the object's composition
If the gate voltage of the MOSFET is kept below threshold voltage to maintain high resistance, then the bias resistance remains stable, but the bias voltage still changes with large signal input, increasing total harmonic distortion
Solution Approach 1:
The invention introduces feedback control through the gate voltage application mechanism. By controlling the gate voltages of the MOSFETs to remain below threshold voltages while responding to signal conditions, the system provides negative feedback that stabilizes the bias voltage and reduces the generation of harmonic distortion, thus resolving the contradiction between resistance stability and distortion reduction
Data Source
AI summary
According to one embodiment, a semiconductor device provided with an input terminal and a resistor circuit is presented. The resistor circuit is provided with first and second transistors, a first resistor, a capacitor and a capacitor. A drain of the first transistor is connected to the input terminal. One end of the first resistor is connected to a gate of the first transistor. A drain of the second transistor is connected to a source of the first transistor. A gate of the second transistor is connected to the other end of the first resistor. A source of the second transistor is connected to a power supply of a source side. The capacitor is connected between the drain and the gate of the first transistor. The voltage supply circuit is connected to the other end of the first resistor and the gate of the second transistor.