GaN on SiC for 5G base stations

Earlier this year, Cisco published an update to their Visual Networking Index¹, predicting a seven-fold increase in mobile data traffic during 2017 – 2022 to reach 77.5 exabytes (EB) per month. This is equivalent to moving data stored on 19 billion DVDs over the mobile network. Every month.

Now, that spells a great commercial opportunity for mobile network operators. But it also indicates a challenge – that of the ability to move all of this data back and forth at a reasonable clip. For, it isn’t just the sheer amount of data that is the trend, but also the type of future applications, such as augmented reality (AR) and vehicle-to-vehicle (V2V) communications, which demand much lower latencies and much higher bandwidth. That spec is met by 5G, the next-generation cellular communications standard.

5G will reside in three frequency bands:

• High-band: This highest-frequency band of greater-than 24 GHz frequencies requires technology innovation, re-design and new materials, and will therefore come at a much greater cost to operators than will the other two bands.
• Mid-band: At sub-6 GHz frequencies, the mid-band offers a significant upgrade to the current 4G standard, and is enabled with today’s innovative component technologies, like gallium nitride (GaN) on silicon carbide (SiC), with much less modification to the system design. A comparatively smaller change in the bill of materials (BOM) means that this band is attractive for first launching 5G and the related data-intensive applications.
  The year 2020 is expected to see significant operator activity in this band as the Release 16 of the 3rd Generation Partnership Project (3GPP) is finalized and allows 5G to operate in unlicensed bands (“NR-U”), such as 5 GHz and 6 GHz.
• Low-band: Lower frequencies – < 2.2 GHz – can also be used for 5G, such as to handle IoT data, but only offer an incremental upgrade over 4G.

Pain points for operators

While the higher 5G frequencies offer a boost in speed and bandwidth, the same high frequencies are more directional and more prone to attenuation of the signal. Also, just increasing the bandwidth doesn’t lead to a linear increase in capacity because the higher bandwidth also leads to a lower signal-to-noise ratio (SNR). This needs to be overcome by boosting the signal, which means increasing the transmit power, increasing the number of antennas, increasing the number of cells, or, as in the case of 5G, exercising all of these options.

The increase in cell density to meet data capacity requirements comes at a cost. And it is likely to decrease both the availability of rooftop and tower locations for hosting base stations.

Operators will need smaller and lighter equipment that can be installed in locations previously not feasible. Moreover, smaller and lighter equipment makes for easier, less expensive installation and may also translate to a lower cell tower rent.

In search of smaller, lighter base stations

Major network equipment vendors have turned to GaN on SiC-based designs and away from traditional silicon (Si)-based devices to meet the high frequency, high power requirements of their base stations.

Whereas laterally-diffused metal-oxide semiconductor (LDMOS) process technology has allowed Si-based devices to progress to higher power densities, they pale in comparison to the high-frequency characteristics of GaN and the superior thermal conductivity of SiC.

GaN on SiC thus enables a system to achieve a much higher power density, which helps reduce the base station size by not requiring much of the thermal management hardware that is necessary with LDMOS.

GaN inside?

GaN’s higher efficiency at 5G frequencies compared with LDMOS also means a lower operating cost per bit/second and a lower carbon footprint. Wolfspeed, a dominant player in the GaN on SiC device market, estimates that GaN on SiC can save over 200 W of DC power compared to a system that uses LDMOS power amplifiers (PAs) when operated at maximum average power.

If you are a network operator talking to equipment vendors about 5G, ask them if they have Wolfspeed’s GaN on SiC components inside.

References

1. Cisco Mobile VNI Forecast and Trends, 2017-2022:
https://www.cisco.com/c/en/us/solutions/service-provider/visual-networking-index-vni/index.html#~mobile-forecast

2. 5G’s Impact on Telecom Infrastructure 2019:
https://www.i-micronews.com/products/5gs-impact-on-telecom-infrastructure-2019/