Modular 64-Channel MEMS Mic Array with High-Speed Serialized Audio

This automotive R&D project required the design of a high-channel-count MEMS microphone acquisition system capable of delivering synchronized, low-latency, and phase-accurate audio to an FPGA for beamforming and noise source localization.
The solution supports up to 64 MEMS microphones organized into modular circular arrays of 16 microphones each, connected via automotive-grade high-speed serial links. The design ensures timing coherence, signal integrity, and EMI immunity in the demanding conditions of in-vehicle testing.

System Architecture & FPD-Link

Each circular microphone array board integrates:

16x high-SNR MEMS microphones, positioned for uniform spatial coverage.
2x Texas Instruments audio codecs – each codec supports up to 8 microphone channels.
1x TI Serializer (DS90UA101) – aggregates multi-channel I²S streams into a single high-speed differential link.
Automotive Rosenberger RF connector – ensures a shielded, mechanically robust interface to the receiver board.

The receiver board contains:

4x TI Deserializers (DS90UA102) – each linked to one microphone board.
FMC interface – connects directly to a Xilinx FPGA board for real-time capture and DSP.
Common clocking system – maintains phase alignment across all boards.

Why FPD-Link III was chosen:
Texas Instruments’ FPD-Link technology was selected for its ability to serialize multiple I²S channels over a single twisted-pair differential link, replacing bulky parallel buses.
In this design:

The serializer multiplexes all I²S channels from the codecs into a high-speed stream.
The deserializer recovers each I²S channel with precise clock phase alignment.
This ensures low jitter, phase coherence, and strong EMI immunity, all essential for beamforming and automotive environments.

How MEMS Microphones Communicate with the Codec

Each MEMS microphone used in this system is a digital PDM (Pulse Density Modulation) microphone.

Clocking – The codec provides a PDM clock to each microphone input, typically in the range of 1–3 MHz.

Data Transmission – The MEMS microphones output a PDM bitstream representing the instantaneous audio signal as a sequence of 1-bit samples.

Decimation & Conversion – The audio codec contains a PDM-to-PCM decimation filter, converting the high-frequency PDM stream into standard PCM audio samples (typically 24-bit at 48 kHz).

I²S Output – The codec transmits these PCM samples to the serializer using the I²S protocol (BCLK, WS, DATA lines), synchronized across all channels.

This architecture eliminates the need for each microphone to have a full PCM interface and allows tight clock domain control, which is critical for maintaining phase alignment between channels.

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PCB Layout & Routing Considerations

Achieving reliable performance required strict adherence to signal integrity and timing rules:

PDM Trace Matching – Length-matched PDM clock and data lines from MEMS microphones to codec inputs to ensure synchronous sampling between channels.

I²S Timing Alignment – BCLK, WS, and DATA traces from codecs to the serializer were matched in length to maintain phase-coherent data arrival.

Differential Pair Integrity – High-speed FPD-Link III differential pairs routed with controlled impedance (100 Ω differential) and minimal intra-pair skew.

Noise Isolation – Split ground planes for analog (MEMS) and digital (serializer/FPGA) sections, connected at a single point for reference stability.

Radial Symmetry in PCB Geometry – Circular layout ensured consistent trace lengths from each microphone to the codec, improving beamforming accuracy.

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Key Achievements:

64-channel synchronized capture at 24-bit/48 kHz
Low-latency serialized transmission with phase alignment maintained
EMI-resilient automotive-grade interconnect using Rosenberger connectors
Reduced cable complexity – single differential link replaces multiple parallel buses
Scalable design – add arrays without changing the receiver architecture

Applications:

Automotive acoustic beamforming for noise detection and source tracking
Interior cabin noise analysis for comfort tuning
Exterior environmental sound capture for ADAS & AV algorithms
Dataset acquisition for AI-based acoustic modeling

Outcome:
The final system provided the client with a reliable, high-resolution, phase-accurate multi-channel audio acquisition platform.
Its modular design allowed flexible deployment — from a single 16-mic array to a full 64-channel configuration — without altering the signal processing backend.