Microphone Differential Circuit for Parasitic Capacitance Noise
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Solution Overview
Problem
Traditional single-end-to-differential microphone circuits face challenges due to parasitic capacitance from the MEMS microphone substrate, leading to non-ideal differential signals and increased noise in fully differential amplifiers, which negatively impacts the signal-to-noise ratio.
Innovation Solution
The proposed single-end-to-differential microphone circuit employs a current sharing amplifier with a small input common mode voltage range and low noise, utilizing a signal processing module to adjust the output signals of primary amplifiers to achieve equal vibration amplitude and adverse phase differential signals, thereby improving signal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fully differential amplifier with a large input common mode voltage range is used to accommodate the non-ideal differential signal, then the amplifier can work normally, but the noise increases and the signal-to-noise ratio deteriorates
Solution Approach 1:
The patent applies preliminary action by adjusting the differential signal before it reaches the amplifier. The signal processing module pre-adjusts the amplitude and phase of the differential signal to meet ideal requirements, so that when the signal enters the amplifier, the amplifier can use a smaller input common mode voltage range and achieve lower noise performance.
Solution Approach 2:
The patent introduces an intermediary component - the signal processing module - between the MEMS microphone and the amplifier. This intermediary adjusts the non-ideal differential signal to an ideal form, allowing the amplifier to operate with optimal noise characteristics rather than requiring a large input common mode voltage range.
2Device complexity
If the substrate of the MEMS microphone is directly connected to the negative input end of the fully differential amplifier, then the circuit structure is simple, but the parasitic capacitance causes non-ideal differential signals with unequal amplitude and opposite phase
Solution Approach 1:
The signal processing module serves as an intermediary that corrects the differential signal quality. It compensates for the effects of parasitic capacitance by adjusting the amplitude and phase of the signals, transforming non-ideal differential signals into ideal ones without requiring complex circuit reconfiguration.
Solution Approach 2:
The patent changes the parameters of the differential signal through the signal processing module. By adjusting voltage levels, phase relationships, and amplitude balances, the module transforms signals that would otherwise be degraded by parasitic capacitance into ideal differential signals suitable for low-noise amplification.
Data Source
AI summary
The present invention provides a single-end-to-differential microphone circuit, including a power supply end for inputting a first bias voltage, a microphone capacitor, a coupling capacitor, a first primary amplifier, a second primary amplifier, a signal processing module, current sharing amplifier, a feedback resistor at positive end, a feedback capacitor at positive end, a feedback resistor at negative end, a feedback capacitor at negative end. Compared with the prior art, the single-end-to-differential microphone circuit of the present invention can utilize the current sharing amplifier with a small input common mode voltage range and low noise to realize the single-end-to-differential of the signal, which is beneficial to improve the signal to noise ratio of the circuit.