Parallel Analog-Digital Filter Circuit for Noise Delay Compensation
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Solution Overview
Problem
Existing noise canceling systems using analog circuits face challenges in achieving sufficient noise reduction due to digital delay issues when employing sigma-delta type analog/digital converters or digital/analog converters, which are expensive and not suitable for consumer applications, while digitalization offers benefits like mode selection and high sound quality but is hindered by digital delay.
Innovation Solution
A filter circuit and noise canceling system that combines a digital section with an analog path, using an analog/digital conversion section, a non-adaptive digital filter, and a digital/analog conversion section, where the analog path outputs the noise signal either unprocessed or processed by an analog filter, and a synthesis section combines these signals for noise reduction, compensating for frequency bands and noise levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a sigma-delta type analog/digital converter or digital/analog converter is used to form noise canceling systems from digital circuits, then digitalization benefits such as mode selection and high sound quality are achieved, but significant digital delay occurs and sufficient noise reduction cannot be achieved
Solution Approach 1:
The filter circuit is divided into two parallel sections: a digital section (including ADC, digital filter, and DAC) and an analog path. Each section processes the noise signal independently and contributes to the final noise reduction signal, allowing the system to leverage both digital and analog processing advantages while compensating for their individual limitations.
Solution Approach 2:
The digital section and analog path are merged in parallel to process the noise signal simultaneously. Their outputs are combined to produce the final noise reduction signal, integrating the adaptability and sound quality benefits of digital processing with the real-time response advantage of analog processing to overcome digital delay.
2Speed
If sequential conversion type ADC or DAC is used to achieve high speed conversion, then digital delay is reduced, but the cost becomes expensive and not suitable for consumer appliances
Solution Approach 1:
The system combines a standard-speed sigma-delta type ADC/DAC (low cost) with an analog path to achieve the noise reduction performance that would otherwise require expensive high-speed sequential conversion type converters. The analog path compensates for the conversion delay, enabling cost-effective implementation.
Solution Approach 2:
The analog path acts as an intermediary that compensates for the delay introduced by the low-cost sigma-delta ADC/DAC. By processing the noise signal through the analog path in parallel, the system achieves the necessary timing characteristics without requiring expensive high-speed converters.
3Adaptability or versatility
If only digital processing is used for noise canceling, then mode selection and digital equalization are achieved, but noise reduction performance is insufficient due to digital delay
Solution Approach 1:
The noise canceling system is segmented into digital processing (for mode selection and equalization) and analog processing (for real-time noise reduction). Each segment performs its specialized function, with the analog path ensuring sufficient noise reduction performance while the digital section provides adaptability and sound quality enhancement.
Solution Approach 2:
The digital section and analog path are merged to combine the benefits of digital equalization and mode selection with reliable noise reduction performance. The analog path's real-time processing capability ensures sufficient noise reduction while the digital section provides user-configurable features.
Data Source
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Figure 2A~2B
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AI summary
There is provided a filter circuit for producing a noise reduction signal for reducing a noise signal collected by a microphone, including: a digital section including an analog/digital conversion section configured to convert the noise signal into a digital noise signal, a digital filter section configured to produce a digital noise reduction signal based on the digital noise signal, and a digital/analog conversion section configured to convert the digital noise reduction signal into an analog noise reduction signal; an analog path connected in parallel to said digital section and configured to output the noise signal as it is or after processed by an analog filter; and a synthesis section configured to synthesize the analog noise reduction signal outputted from said digital/analog conversion section of said digital section and the analog signal outputted from said analog path to produce a noise reduction signal to be used for noise reduction.