Real-Time Controller Board

Partners: LAUM (Le Mans University), CNRS.

The Real-Time Latency Challenge

To stabilize an acoustic control loop, every microsecond counts. At a 96 kHz sampling rate, the processor has less than $10.4~\mu s$ to acquire the signal, solve non-linear Ordinary Differential Equations (ODEs), and update the output.

Critical Technology Choices

• Processor: Teensy 3.6 (ARM Cortex M4 @ 180 MHz) selected for its Floating Point Unit (FPU) and overall robustness.
• ADC Architecture (SAR): Utilized SAR (Successive Approximation Register) converters to minimize conversion latency compared to Sigma-Delta architectures.
• High-Resolution DAC: SPI extension to upgrade from 12-bit to 16-bit (DAC8831) to preserve the compensation signal’s dynamic range.

Electronics and Hardware Design

The board was designed to isolate high-speed digital signals from sensitive analog sections. The final prototype is integrated into a shielded enclosure with BNC connectors for laboratory environments.

Internal Architecture

V3 Enclosure layout: shielding, power supply, and Teensy integration.

Control PCB

Dual-layer design optimized to minimize noise floor (12.3 ENOB).

PCB Layout (Altium Designer)

Component placement was optimized to separate power, analog, and digital domains on a dual-layer circuit.

🔎 Annotated Layout

Functional block visualization of the V3 Controller.

• Input Conditioning: OPA2325 based stage providing the $1.65~V$ DC offset (bias) and ADC input protection.
• Anti-aliasing Filter: 2nd order filter calculated with an $11~kHz$ cutoff frequency.
• Bipolar Output: The DAC8831 is coupled with an ADA4084 precision amplifier to generate a symmetrical audio signal ($\pm~V$).

Characterization and Performance

The controller was validated through a series of high-resolution tests. These three analyses confirm that the board provides sufficient fidelity for compensation algorithms while maintaining minimal latency.

Spectral Purity (1 kHz)

75.6 dB SINAD and 12.3 bits ENOB without signal averaging.

Multitone Analysis

Dynamic range validation across the entire useful audio spectrum.

Frequency Response

Stable passband from 7 mHz to 11 kHz (4th order filtering).

Specifications Summary (V3)

References and Publications