Differential Microphone Feedback Circuit for Higher SNR
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Solution Overview
Problem
Traditional single-ended to differential microphone circuits face challenges in maintaining a high signal-to-noise ratio due to the sensitivity of the signal-to-noise ratio to changes in the feedback capacitor, especially when the equivalent capacitor of the microphone becomes smaller.
Innovation Solution
The proposed solution involves a single-end-to-differential microphone circuit that includes an amplifier, a microphone, a coupling capacitor, and feedback capacitors and resistors. A bias resistor is used to enable AC signal input at both ends of the amplifier, allowing for a balanced communication within the microphone and improving the signal-to-noise ratio by doubling the size of the feedback capacitor relative to the microphone capacitor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the feedback capacitor CFB is reduced to maintain closed loop gain as 1 when CMEMS becomes smaller, then the circuit can work with smaller microphones, but the signal-to-noise ratio at the output end becomes worse
Solution Approach 1:
The feedback capacitor is divided into two separate capacitors (CFB1 and CFB2) connected to the negative and positive output ends of the amplifier respectively. This segmentation allows the total feedback capacitance to be doubled (CFB = CFB1 + CFB2 = 2CMEMS) while maintaining the closed-loop gain of 1, thereby improving the signal-to-noise ratio without requiring larger microphone capacitors
Solution Approach 2:
The patent combines the feedback paths to both output ends of the differential amplifier, merging the feedback function across both sides. This allows the feedback capacitance to be effectively doubled while maintaining the same closed-loop gain, resolving the contradiction between small capacitor size and high signal-to-noise ratio
2Ease of operation
If the vibration amplitude of the input signal is large, then the common mode voltage VIN,CM has large vibration amplitude, but this requires an amplifier with input common mode voltage of a large range
Solution Approach 1:
The patent extracts the common mode signal component from the differential signal path by using a dedicated common mode rejection amplifier. The common mode voltage is separately processed and subtracted from the differential output, allowing the main differential amplifier to operate with a limited common mode voltage range while still handling large input signal amplitudes
Solution Approach 2:
The patent introduces a common mode rejection amplifier as an intermediary component that handles the common mode voltage separately. This intermediary processes the common mode signal and feeds it back to cancel out common mode vibrations, enabling the main amplifier to maintain a small input common mode voltage range while accommodating large input signal amplitudes
Data Source
AI summary
The present invention provides a single-end-to-differential microphone circuit and an electronic equipment, including: an amplifier, a microphone connected to the positive input end of the amplifier, a coupling capacitor CAC connected to the negative input end of the amplifier, a first feedback capacitor CFB1 connected to the negative output end of the amplifier, a first feedback resistor RFB1 connected in parallel with the first feedback capacitor CFB1, a second feedback capacitor connected to the positive output end of the amplifier CFB2, and a second feedback resistor RFB2 connected in parallel with the second feedback capacitor CFB1. The circuit of the present invention can adopt a microphone structure with smaller capacity, and at the same time has a better system signal to noise ratio.