Microphone Output Load Control for Low Distortion at High SPL
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Solution Overview
Problem
Microphones operating in a two-terminal mode exhibit higher distortion levels at low sound pressure levels, limiting their effectiveness compared to three-terminal microphones, and struggle to handle high sound pressure levels above 110-120 dB SPL due to limitations in the output stage.
Innovation Solution
An electronic circuit with an adjustable output load and automatic control circuit that adjusts the current draw of the output stage based on captured sound pressure levels, allowing for reduced distortion and increased sound pressure handling up to 130 dB SPL or higher, while also enabling flexible sensitivity adjustments through a two-terminal mode configuration network and integrated resistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the output stage operates with low quiescent current levels to reduce power consumption, then power efficiency is improved, but distortion levels increase at high sound pressure levels
Solution Approach 1:
The patent implements dynamic adjustment of the output load resistance based on the detected sound pressure level. The control circuit monitors the input signal level and automatically adjusts the load resistance to optimize the operating point of the class A amplifier, allowing it to maintain low distortion performance at high SPL while consuming minimal power at low SPL.
Solution Approach 2:
The patent changes the electrical parameters (load resistance value) of the output stage based on the operating conditions. By varying the load resistance according to the sound pressure level, the amplifier's operating point is optimized dynamically, resolving the contradiction between power consumption and distortion performance.
2Device complexity
If the output load is fixed to simplify the circuit design, then device complexity is reduced, but the microphone cannot handle high sound pressure levels above 110-120 dB SPL
Solution Approach 1:
The patent introduces a dynamic load adjustment mechanism that automatically adapts the output load resistance to the detected sound pressure level. This dynamic adaptation enables the microphone to handle high SPL applications while maintaining a relatively simple overall circuit architecture based on a class A amplifier.
Solution Approach 2:
The patent implements a feedback control mechanism where the control circuit monitors the input signal level and uses this information to adjust the output load resistance. This feedback loop enables the system to automatically optimize its performance for different sound pressure levels without requiring complex manual configuration.
3Ease of manufacture
If the microphone operates in two-terminal mode to reduce wiring and production costs, then ease of manufacture is improved, but distortion levels increase at low sound pressure levels
Solution Approach 1:
The patent applies dynamic load adjustment in the two-terminal microphone configuration, where the control circuit detects the sound pressure level and automatically adjusts the output load resistance to minimize distortion. This dynamic adaptation enables two-terminal microphones to achieve distortion performance comparable to three-terminal configurations while maintaining the manufacturing advantages of the two-terminal architecture.
Data Source
AI summary
The electronic circuit having an input stage for pre-amplifying an electrical input signal of the electronic circuit provided by a transducer. The electronic circuit has an output stage for providing a microphone output signal by processing an output signal of the input stage. The electronic circuit has an adjustable output load arranged and configured for setting a current draw of the output stage. Additionally, the electronic circuit has a measurement circuit configured to capture the output signal of the input stage and an automatic control circuit configured to adjust the adjustable output load dependent on the captured output signal of the input stage.