MEMS Speaker Crossover Circuit for Wideband Audio and Low Phase Shift
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Solution Overview
Problem
Micro Electro Mechanical System (MEMS) speakers typically use a single membrane type, limiting their design flexibility and sound quality due to the maximum input frequency being around 15-17 KHz, which is insufficient to cover the entire human audible range effectively.
Innovation Solution
A crossover circuit is introduced within the sound producing device, comprising a first and second sound producing cell driven by distinct driving signals, with a filter and subtraction circuit configuration that partitions the input signal into complementary audio bands, allowing the device to produce sound across a broader frequency spectrum while minimizing phase shift.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a single membrane type is used in MEMS speakers, then the device structure is simple and manufacturing is easier, but the maximum input frequency is limited to 15-17 KHz and sound quality is restricted
Solution Approach 1:
The audio frequency range is segmented into high-frequency and low-frequency bands using a crossover circuit. The high-frequency signal drives a first sound producing cell with a first membrane optimized for high frequencies, while the low-frequency signal drives a second sound producing cell with a second membrane optimized for low frequencies. This segmentation allows each membrane to be specialized for its frequency range, extending the overall frequency coverage beyond 15-17 KHz while maintaining manageable complexity through functional division.
2Adaptability or versatility
If multiple sound producing cells are used to cover different frequency ranges, then the frequency coverage is extended, but phase shift between aggregated sounds increases
Solution Approach 1:
The crossover circuit incorporates feedback mechanisms to monitor and adjust the phase relationships between the high-frequency and low-frequency sound producing cells. By detecting phase shifts in the aggregated sound and applying corrective phase adjustment, the system maintains phase coherence across the extended frequency range, ensuring reliable and high-quality audio output despite using multiple specialized membranes.
3Adaptability or versatility
If multiple sound producing cells are used to extend frequency range, then audio quality improves, but power consumption increases
Solution Approach 1:
The crossover circuit is designed to direct only the necessary frequency components to each sound producing cell, avoiding unnecessary power consumption. The high-frequency cell receives only high-frequency signals and the low-frequency cell receives only low-frequency signals, with each cell operating at optimal efficiency for its designated range. This partial action approach extends frequency coverage while minimizing total power consumption by avoiding over-driving cells beyond their optimal ranges.
Data Source
AI summary
A crossover circuit, disposed within a sound producing device including a first sound producing cell driven by a first driving signal and a second sound producing cell driven by a second driving signal, includes a first filter receiving an input signal at an input terminal of the first filter, a first subtraction circuit, and a second filter coupled between the output terminal of the first filter and the second input terminal of the first subtraction circuit. A first input terminal of the first subtraction circuit is coupled to the input terminal of the first filter; a second input terminal of the first subtraction circuit is coupled to an output terminal of the first filter. The crossover circuit produces the first driving signal and the second driving signal according to a first output signal of the first subtraction circuit and a second output signal of the first filter respectively.