Microphone Preamplifier Feedback Circuit for Lower Harmonic Distortion
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Solution Overview
Problem
Conventional preamplifying circuits for microphone sensors suffer from significant harmonic distortion, especially when dealing with large amplitude input signals, due to parasitic diodes in CMOS processes, which hinder the effective series connection of diodes and degrade sound quality.
Innovation Solution
A preamplifying circuit design featuring a series connection of first and second amplifiers with a positive feedback branch, including a diode group in inverse parallel connection, and additional capacitors and diodes for filtering and DC biasing, which reduces harmonic distortion by feeding back signals and attenuating AC signals, thereby improving sound quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If diodes are connected in series to reduce harmonic distortion, then harmonic distortion is reduced, but parasitic diodes in CMOS process prevent the series connection effect from being realized
Solution Approach 1:
The patent introduces an operational amplifier as an intermediary component between the diodes. The op-amp's high input impedance and low output impedance characteristics allow it to decouple the parasitic diode effects from the main signal path, enabling the series connection to function properly despite CMOS fabrication constraints. The op-amp acts as a buffer that prevents the parasitic diodes from interfering with the intended series connection behavior.
Solution Approach 2:
The patent changes the operating parameters by using the op-amp to control the voltage and current conditions across the diodes. By adjusting the gain and impedance parameters of the op-amp, the circuit achieves the desired series connection effect while compensating for the parasitic diode characteristics inherent in CMOS processes.
2Power
If diodes are used for signal rectification and amplification, then signal amplification is achieved, but harmonic distortion increases significantly
Solution Approach 1:
The patent employs feedback mechanisms through the operational amplifier to monitor and correct the output signal. The op-amp continuously adjusts its output to maintain the desired signal level while minimizing distortion. This feedback control allows the circuit to achieve high amplification while actively compensating for the nonlinear characteristics of the diodes that would otherwise generate harmonic distortion.
Solution Approach 2:
The operational amplifier serves as an intermediary that linearizes the signal path. By placing the op-amp between the diodes and the output, it provides a low-impedance buffer that prevents the diode nonlinearities from directly affecting the output signal, thereby achieving amplification with minimal harmonic distortion.
3Object-affected harmful factors
If voltage drops across diode group are reduced, then harmonic distortion is reduced, but circuit complexity increases
Solution Approach 1:
The operational amplifier performs multiple functions simultaneously: it provides voltage buffering, impedance transformation, signal amplification, and distortion reduction. This multi-functionality allows a single component to address multiple circuit requirements, reducing the need for additional separate components and thereby limiting the increase in circuit complexity despite the added performance capabilities.
Data Source
AI summary
Provided is a preamplifying circuit, including a first amplifier and a second amplifier sequentially connected in series, wherein an output end of the second amplifier is connected to a circuit output end, and an input end of the first amplifier is connected to a circuit input end. The preamplifying circuit further includes a positive feedback branch including a diode group and a third amplifier, wherein one end of the diode group is connected to the input end of the first amplifier. The positive feedback circuit can positively feed part of signals back to the other end of the diode group, so that voltage drops at two ends of the diode group can be reduced, and harmonic distortion caused by nonlinearity of the diode group is reduced. Thus, the sound quality detected by a microphone sensor is improved.