Digital Microphone Band Splitter for Ultrasonic Signal Detection
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Solution Overview
Problem
Conventional digital microphones face challenges in efficiently detecting ultrasonic and near-ultrasonic frequencies due to high clock frequencies required, which increase power consumption and noise levels, making it difficult to maintain effective signal recovery without prolonged averaging.
Innovation Solution
A digital microphone apparatus that splits the microphone signal into separate frequency bands, down-converts higher frequency bands to lower frequency ranges, and applies selective gain modulation to improve signal-to-noise ratio (SNR) without necessitating high clock rates, using a band splitter, modulation block, and coder to encode signals in a 1-bit oversampled PDM format.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high clock frequencies are used to detect ultrasonic and near-ultrasonic frequencies, then signal recovery capability is improved, but power consumption increases
Solution Approach 1:
The patent segments the frequency spectrum into multiple bands using a band splitter, with each band processed by dedicated signal paths. High-frequency ultrasonic signals are separated from lower frequency audio signals and processed through specific paths optimized for their frequency range, allowing efficient detection without requiring the entire system to operate at high clock frequencies for all frequencies.
Solution Approach 2:
The patent dynamically adjusts the clock frequency based on the detected frequency band. When ultrasonic frequencies are detected, the clock frequency is increased to appropriate levels; when only lower frequency audio is present, the clock frequency is reduced. This adaptive parameter change optimizes power consumption while maintaining signal recovery capability when needed.
2Measurement precision
If high clock frequencies are used to detect ultrasonic frequencies, then signal recovery capability is improved, but noise levels increase
Solution Approach 1:
By segmenting the signal processing into separate frequency bands with dedicated signal paths, the patent isolates ultrasonic frequency processing from lower frequency processing. This segmentation allows noise filtering to be applied specifically to each band, preventing high-frequency noise from contaminating the entire signal spectrum and reducing overall noise levels while maintaining ultrasonic detection capability.
Solution Approach 2:
The patent introduces intermediate processing stages including band-pass filters and frequency-specific gain control between the microphone input and final output. These intermediary components selectively pass or attenuate specific frequency ranges, acting as mediators that prevent noise from one frequency band from affecting another band, thereby reducing overall noise levels while preserving signal recovery.
3Measurement precision
If prolonged averaging is used to recover signals, then signal-to-noise ratio is improved, but response time increases
Solution Approach 1:
The patent applies different processing qualities to different frequency bands. For ultrasonic frequencies where signal recovery is critical, more sophisticated processing including selective gain modulation and filtering is applied. For lower frequency bands where rapid response is prioritized, simpler processing is used. This local differentiation of processing quality improves SNR for ultrasonic signals without requiring prolonged averaging across all frequencies, thus maintaining faster response times.
4Measurement precision
If band splitting and down-conversion are implemented, then signal-to-noise ratio for ultrasonic frequencies is improved, but device complexity increases
Solution Approach 1:
The patent implements band splitting that divides the frequency spectrum into manageable segments processed by separate signal paths. This segmentation allows down-conversion to be applied only to specific frequency bands that require it, rather than the entire spectrum. The modular structure of segmented processing reduces the overall complexity compared to processing the full bandwidth with uniform high-complexity processing.
Solution Approach 2:
The patent extracts and processes ultrasonic frequency components through dedicated signal paths separate from the main audio path. By taking out the ultrasonic band for specialized processing including down-conversion and selective gain modulation, the system improves SNR for these frequencies without requiring complex processing for all frequencies. This extraction approach concentrates complexity only where needed rather than distributing it uniformly.
Data Source
AI summary
This application relates to methods and apparatus for digital microphones. Disclosed is a digital microphone apparatus (300) for outputting a digital output signal (DATA) at a sample rate defined by a received clock signal (CLK). The apparatus includes a band splitter (302) configured to receive a microphone signal (SMD) indicative of an output of a microphone transducer and split said microphone signal into first signal path (SP1) for frequencies in a first band and a second signal path (SP2) for frequencies in a second band, the frequencies of the second band being higher than the frequencies in the first band. A modulation block (304) is configured to operate on the second signal path to down-convert signals in the second signal path from the second frequency band to a lower frequency band.