Microphone Cut-Off Frequency Calibration Using Feedback Loop Gain
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Solution Overview
Problem
Current microphones face limitations in noise reduction and sound quality due to their configuration and operational methods, particularly in controlling the cut-off frequency, which affects their sensitivity and beamforming performance.
Innovation Solution
A system and method for precisely setting the cut-off frequency of a microphone signal by adjusting the loop gain of the processing circuit, using a digital filter in a feedback loop, and combining the acoustic signal with an output from a digital-to-analog converter to filter out low-frequency components, thereby improving sound quality and enabling better beamforming performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the cut-off frequency of the microphone is adjusted to improve noise reduction, then low-frequency noise is filtered out, but the sensitivity and beamforming performance deteriorate due to mismatched frequencies
Solution Approach 1:
The patent changes the cut-off frequency parameter of the microphone by adjusting the loop gain of the processing circuit. By modifying the electrical characteristic (loop gain) rather than the physical structure, the cut-off frequency can be precisely tuned to match specific values, thereby maintaining beamforming performance while still filtering out low-frequency noise.
Solution Approach 2:
The patent employs a feedback loop in the processing circuit where the output is fed back to the input through a digital-to-analog converter. This feedback mechanism allows for precise control of the loop gain, which directly influences the cut-off frequency. By adjusting the feedback strength, the system can achieve the desired cut-off frequency that balances noise reduction with beamforming performance.
2Manufacturing precision
If the loop gain is adjusted to control the cut-off frequency, then precise frequency control is achieved, but the device complexity increases due to additional processing circuit components
Solution Approach 1:
The processing circuit performs multiple functions: it processes the microphone signal, provides feedback control, and simultaneously adjusts the cut-off frequency by modifying the loop gain. The same feedback circuitry that is necessary for signal processing also enables precise cut-off frequency control, eliminating the need for separate adjustment mechanisms and reducing overall device complexity.
3Measurement precision
If microphones are manufactured with closely matched cut-off frequencies to improve beamforming, then beamforming performance is enhanced, but the manufacturing precision requirements increase
Solution Approach 1:
Instead of relying on fixed, precisely manufactured cut-off frequencies, the patent makes the cut-off frequency dynamic and adjustable through loop gain control. This allows the cut-off frequency to be tuned after manufacturing, compensating for variations in production and eliminating the need for extremely tight manufacturing tolerances while still achieving the required frequency matching for optimal beamforming.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for precise control of the microphone's sensitivity and cut-off frequency, enhancing sound quality by filtering out low-frequency noise and enabling the manufacture of microphones with closely matched frequencies for improved beamforming performance.
Implementation Method 1
The processing circuit also includes a feedback loop and, particularly, an internal feedback loop. The feedback loop returns the output of the decimator back to a combination block via an electrical current digital to analog converter (IDAC).
Implementation Method 2
The cut-off frequency is controlled generally by a digital filter in a feedback loop
Implementation Method 3
The processing circuit includes an amplifier for amplifying a microphone signal
Implementation Method 4
an analog to digital converter for converting the amplified microphone signal into a digital signal
Implementation Method 5
a decimator for down sampling a frequency of the digital signal
Implementation Method 6
The feedback loop returns the output of the decimator back to a combination block via an electrical current digital to analog converter (IDAC)
Implementation Method 7
The combination block receives an acoustic signal from a transducer of the microphone and combines that acoustic signal with the output of the feedback loop to obtain the microphone signal
Data Source
AI summary
A system and method in an audio signal electrical circuit including a feedback loop with a digital filter coupled to a current digital to analog converter (IDAC) includes providing an output signal from the IDAC to analog elements of the audio signal electrical circuit, the output signal from the IDAC based upon a reference signal input to the IDAC when an output of the digital filter is not input to the IDAC. The system and method also include comparing an output signal of the audio signal electrical circuit to a reference, and calibrating the audio signal electrical circuit to correspond the output signal of the audio signal electrical circuit to the reference. Calibration of the audio signal electrical circuit enables more precise control of a cut-off frequency of a microphone signal when the output of the digital filter is input to the IDAC.