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ICs and software synchronize Open RAN networks

The Si55xx and Si540x timing ICs from Skyworks work in tandem with AccuTime software to provide low-jitter clocks and IEEE 1588 PTP fronthaul sync.

ics and software synchronize open ran networks

Figure 1. Timing ICs from Skyworks keep wireless networks and wired networks in sync.

In networks, timing is everything. Without solid, accurate timing and synchronization, data gets lost. Skyworks has introduced ICs that work with its software to address the timing relative to 5G radios and the fronthaul wired networks that connect to them. Open RAN networks, which disaggregate functions from the radio through the fronthaul, consist of radio units and distribution units that need to stay in sync at all times, even when they lose access to GNSS timing signals.

The NetSync Network Synchronizer Clocks consist of the Si55xx and Si540x series. The devices work with the company’s AccuTime network timing software.

Starting with hardware, the Si55xx series (see table in link for datasheets) provide 1588 Precision Time Protocol (PTP) timing that can add full timing support (FTS), partial timing support (PTS), assisted partial timing support (APTS), and PTP-unaware networks for eCPRI fronthaul links.

The Si5518 and Si5512 combine general-purpose clocking and 5G JESD204B clocking for the eCPRI Ethernet PHY, baseband processors, and data converters (transceivers) in 5G macro base stations and small cells (Figure 1). They can keep the radios and networks in sync at data rates to 25 Gb/sec. The devices also serve to reduce jitter that accumulates as signals pass through the fronthaul network.

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Figure 2. Timing functions can integrate into one or two devices depending on design requirements.

Figure 2 shows two configurations. In the top diagram, the Si5518 combines the clocking functions into a single device with 18 clock outputs. The Si5512 has 12 outputs. In the lower diagram, the functions reside in two devices for boards that use a split design. In that option, the Si5512 combines with the Si5508 and Si5510 Wireless Jitter Attenuator Clocks to provide all the functions in the Si5518. The table shows several specs for the Si5518, including its maximum jitter of 130 fs, which Skyworks claims is lower than its competitors by at least 70 fs.

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Specification for SI5518

The Si540x series Network Synchronizer Clocks work in a distribution units (DUs). These devices provide the jitter and wander filtering required for Synchronous Ethernet (SyncE). Each of the clock outputs has software-adjustable delay and skew with 1 ppt resolution. The number of outputs vary depending on the part number’s letter suffix. For example, the Si5401B supports ten clock outputs while the Si5401Q supports 18 outputs.

While networks need stable, low-jitter clocks, they also need to distribute that timing to network nodes. That’s where AccuTime software comes in. AccuTime lets you implement IEEE 1588 time synchronization into your network (Figure 3). The software provides an IEEE 1588 Precision-Time Protocol (PTP) protocol stack and a Time-Recovery Servo, which keeps a network synchronized even when GPS fails or the signal drops.

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AccuTime software provides a complete PTP protocol stack.

AccuTime supports Full Timing Support (ITU-T G.8275.1), Partial and Assisted Partial Timing Support (ITU-T G.8275.2) and PTP-unaware networks (ITU-T G.8261). It also supports Grandmaster clock, Boundary clock, and Slave clock functions. It uses packet selection and adaptive algorithms which, together with the high-resolution digitally controlled oscillator capabilities of the Si55xx and Si540x clocks, provide stringent ITU-T G.8273.1 Class C and Class D timing FTS networks. Networks can meet the 1.1 µs and 15 ppb requirements needed in PTS and APTS networks.

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