Multi-device synchronization is essential for satellite D2D/IoT payloads employing large phased-array antennas, where multiple RF transceivers must operate coherently to support accurate beamforming. Any timing or phase mismatch can degrade beamforming performance, reducing link margin and overall system efficiency. Precise timing and phase alignment across multiple devices must remain throughout the entire system life cycle, including initial bring-up, subsequent JESD204B and JESD204C link reinitializations, and power-on resets.

Achieving this requires three key synchronization capabilities:

1. Phase aligned device clocks for SYSREF to latch;
2. SYSREF-based deterministic data path latency;
3. Synchronized NCO operation to maintain consistent digital frequency and phase relationships across devices

The first capability relies on clock distribution devices and optimized layout to minimize the propagation delay variation across multiple devices. The SYSREF signals must meet the setup and hold time requirements of device clock.

The AFE8030 supports multiple approaches to achieve the SYSREF-based deterministic latency. One approach is to use single-shot SYSREF. In single-shot mode, the SYSREF signal is a single pulse, which is given simultaneously to all the RF transceivers on the board. When all transceivers receive SYSREF at exactly the same instant with respect to the device clocks, they become phase-synchronized. It is also possible to use general-purpose input/output (GPIO)-based control to enable SYSREF latch. In this mode, the SYSREF can operate in continuous sysref mode. All RF transceivers latch to the first device clock rising edge after receiving a GPIO-based latch enable signal. All subsequent pulses are ignored. This approach only requires routing a CMOS GPIO signal to the RF transceivers, which makes this method relatively simpler to implement compared to the single-shot SYSREF method, as it can be challenging to route a differential signal to multiple AFEs on the board with matched lengths. At the same time, this approach requires synchronizing one GPIO per AFE from the host, which can be challenging if the host ASIC or FPGA does not have enough GPIOs.

When it comes to synchronizing NCOs across devices, the simplest way to achieve phase synchronization is to choose transmitter and receiver NCOs that are integer multiples of the SYSREF frequency. This method works well for both single-shot and continuous SYSREF modes, as it does not need any extra mechanism to synchronize the NCOs for transmit and receive across multiple analog front-end devices. It does not matter even if all transceivers latched on different sysref edges. Figure 5-7 shows how in this mode, it does not matter even if all analog front ends latched on different sysref edges.

Figure 5-8 shows the histogram of the phase difference between TX outputs of two devices over power cycles, where on the left side, the NCO phases are not synchronized, therefore the phase difference over power cycles is random; on the right side, the NCO phases across multiple devices are synchronized with SYSREF-based latch, therefore the phase difference over power cycles is retained within a tight deviation, approximately 1.5 degrees.