64-element 28 GHz digital beamformer
NEPTUNE is a 64-element digital beamformer built from four identical chiplets. Each chiplet processes signals locally and passes partial results to its neighbors, reducing the data sent to a central processor.
Distributed processing
Each chiplet serves 16 antenna elements and computes partial beams. Combining those partial beams gives the same result as centralized beamforming. The chiplets use a spiral arrangement that allows the array to grow using the same chip design.
Chip-to-chip communication
A Streaming-AIB interface carries data between chiplets over 13 lanes at 1 Gbps per lane. Its reported energy efficiency is 1.4 pJ per bit. Phase-locked loops synchronize the chiplets so their signals can be combined coherently.
Hardware and measurements
The four chiplets sit on a custom 15-layer LTCC substrate with an 8 × 8 array of 28 GHz patch antennas. Reported measurements include 23 mW per beam-channel and a 20 dB noise figure. Measured beam patterns agree with simulation across steering angles. The paper above describes the implementation and test setup.