Microphone Circuit Topology for Low Impedance Noise Reduction
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Solution Overview
Problem
Conventional microphones suffer from high output impedance and noise issues due to the placement of high-pass filters, which cause signal distortion and increased noise levels, especially at low frequencies.
Innovation Solution
A microphone design that omits a filter circuit between the microphone unit and the HOT terminal and includes a low-pass filter only between the microphone unit and the COLD terminal, maintaining low output impedance across all frequency regions and reducing noise by canceling low-frequency components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a high-pass filter is disposed in a preceding stage of the output circuit to reduce wind noise and vibration noise, then noise reduction is improved, but the output impedance becomes high at low frequencies leading to increased noise level and signal distortion
Solution Approach 1:
The patent removes the high-pass filter from the circuit configuration. By extracting this problematic component, the invention eliminates the source of high output impedance at low frequencies while still achieving noise reduction through alternative means (electronic noise reduction circuitry)
Solution Approach 2:
The patent replaces the passive mechanical/electrical high-pass filter with active electronic noise reduction circuitry. This substitution allows for noise reduction without the impedance-matching problems inherent in passive filter designs
2Reliability
If the input impedance of the high-pass filter is reduced to match the output impedance of the microphone unit, then impedance matching is improved, but distortion of output signals increases
Solution Approach 1:
The patent removes the high-pass filter entirely, eliminating the impedance matching conflict. Without this filter component, there is no need to compromise between impedance matching and signal distortion
3Reliability
If a buffer amplifier with emitter follower circuit is employed to handle the high output impedance of the high-pass filter, then impedance buffering is improved, but noise level significantly increases at frequencies below cutoff frequency
Solution Approach 1:
The patent removes the high-pass filter that created the need for the buffer amplifier. By extracting the root cause (the filter), the subsequent noise-problematic buffer amplifier becomes unnecessary
4Reliability
If the impedance of the resistor in the high-pass filter is increased, then filter performance is improved, but noise level output from the microphone unit increases
Solution Approach 1:
The patent removes the high-pass filter containing the problematic resistor. By extracting this component, the invention eliminates the trade-off between filter performance and noise generation
Data Source
AI summary
A microphone comprises a microphone unit; and a HOT terminal and a COLD terminal that produce a balanced output of output signals of the microphone unit, and no filter circuit is disposed between the microphone unit and the HOT terminal and a low-pass filter is disposed only between the microphone unit and the COLD terminal.