# NEPTUNE

Distributed digital beamformer. **Venue:** IEEE OJ-SSCS 2025.

NEPTUNE is a 64-element 28 GHz digital beamformer in 40nm CMOS for 5G, satellite communication, and defense applications. Conventional systems send raw ADC data over power-hungry SERDES links to a central processor; NEPTUNE uses distributed chiplet processing instead.

## Distributed Processing

Each 16-element chiplet computes partial beams locally, then daisy-chains results to adjacent chips. Because beamforming is linear, this is mathematically equivalent to centralized processing but 30× more power-efficient at 64 elements. A spiral tiling geometry scales to hundreds of elements using a single chiplet design.

## Streaming-AIB Interface

Chip-to-chip communication uses Streaming-AIB, a modified AIB interface adapted for synchronous beamforming: 13 lanes at 1 Gbps, 1.4 pJ/bit efficiency (10× better than JESD204C). Multi-chip PLL synchronization ensures coherent beamforming across dies.

## System Integration

Four chiplets mount on a custom 15-layer LTCC substrate with an 8×8 array of 28 GHz patch antennas. Over-the-air characterization required custom millimeter-wave signal generation, precision mechanical positioning, and cryogenic transient testing. 23 mW per beam-channel, 20 dB noise figure, Streaming-AIB BER of 3×10⁻¹². Measured beam patterns match simulation across steering angles.

- [Paper (PDF)](/portfolio/pdf/neptune.pdf)