MEMS Microphone Output Load Control for Low-THD Two-Terminal Operation
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Solution Overview
Problem
Microphones operating in a two-terminal mode exhibit higher distortion levels at low sound pressure levels compared to those in a three-terminal mode, limiting their effectiveness at high sound pressure levels.
Innovation Solution
An electronic circuit with an adjustable output load and automatic control circuit that adjusts the current draw based on sound pressure levels, combined with a measurement circuit and peak detector, to reduce total harmonic distortion (THD) and extend the microphone's usable range to 130 dB SPL and above, while allowing operation in a two-terminal mode with minimal wiring and reduced production costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If microphones are operated in two-terminal mode with minimal wiring, then ease of manufacture and device complexity are improved, but distortion levels increase at low sound pressure levels
Solution Approach 1:
The patent implements dynamic adjustment of the output load impedance based on the detected sound pressure level. The control circuit continuously monitors the input signal and adjusts the output load to maintain optimal distortion performance across varying SPL conditions, enabling two-terminal operation with reduced distortion
Solution Approach 2:
The patent changes the electrical parameters (output load impedance, current draw) of the output stage based on the detected sound pressure level. By dynamically adjusting these parameters, the system maintains low distortion performance in two-terminal mode while accommodating high sound pressure level operation
2Object-generated harmful factors
If the output load is adjusted to reduce distortion at high sound pressure levels, then distortion performance is improved, but current consumption increases
Solution Approach 1:
The system dynamically adjusts the output load impedance based on the detected sound pressure level. At low SPL, higher impedance reduces current consumption, while at high SPL, lower impedance reduces distortion. This dynamic adaptation resolves the trade-off between power efficiency and distortion performance
Solution Approach 2:
The control circuit continuously monitors the input signal level and periodically adjusts the output load configuration. This periodic adaptation ensures optimal performance is maintained while minimizing power consumption during low-level signals
3Object-generated harmful factors
If the output stage draws higher current to reduce distortion at high sound pressure levels, then distortion performance is improved, but the complexity of control increases
Solution Approach 1:
The patent implements a feedback mechanism where the control circuit monitors the input signal level and adjusts the output load accordingly. This closed-loop control automatically optimizes distortion performance without requiring complex external control systems
Solution Approach 2:
The output stage automatically adjusts its own operating conditions based on the detected signal level. The control circuit is integrated within the microphone module, making the system self-regulating and reducing the need for external complexity
Data Source
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AI summary
The electronic circuit (10)comprises an input stage (Pre_amp)for pre-amplifying an electrical input signal of the electronic circuit (10)provided by a transducer (MEMS). Furthermore, the electronic circuit (10)comprises an output stage (T_amp)for providing a microphone output signal by processing an output signal of the input stage (Pre_amp). The electronic circuit (10)comprises an adjustable output load (RS)arranged and configured for setting a current draw of the output stage (T_amp). Additionally, the electronic cir- cuit (10)comprises a measurement circuit(P_det)configured to capture the output signal of the input stage (Pre_amp)and an automatic control circuit (ACC) configured to adjust the adjustable output load (RS)dependent on the captured output signal of the input stage (Pre_amp).