December 21, 2021
Future entertainment systems and work-at-home environments are rapidly moving toward greater two-way interaction, which calls for enhanced downstream bandwidth and upstream capabilities. To stay competitive in the evolving CATV business, innovative technologies are needed to keep up with demands. One component that can play a vital role in this evolution is the CATV amplifier based on gallium nitride (GaN) technology. This post provides insight into how to do just that. The following is an excerpt from a Qorvo white paper, How to Increase Downstream Bandwidth and Upstream Capabilities in CATV Amplifiers with Greater Efficiency.
Typical allocations for upstream traffic on Hybrid Fiber Coax (HFC) networks in the US range from 5 MHz to 42 MHz. User activities and new use cases are driving the need for increased capacity. In response, some multiple system operators (MSOs) are setting mid-splits or high-splits within the available bandwidth to accommodate these demands, reducing downstream bandwidth and possibly curtailing content or services.
MSOs facing this challenge are exploring the options available through DOCSIS 3.1 or DOCSIS 4.0 specifications. Upstream capacity within DOCSIS 3.1 can be extended up to 204MHz. While DOCSIS 4.0 allows the upstream to go up to 684MHz in both full duplex (FDX) and extended spectrum DOCSIS (ESD). Figure 1 shows how full duplex (FDX) let upstream and downstream traffic share the 684 MHz frequency range.
Take a Deeper Dive
Figure 1. DOCSIS 4.0 FDX spectrum for upstream (US) and downstream (DS).
The trend toward extended CATV bandwidth has led engineers and system architects to explore new technologies as networks are upgraded, requiring a newer generation of passive and active products. To meet demands for the increased bandwidth and data rates, CATV amplifiers must maintain a higher linear output power.
Gallium Nitride (GaN) devices can deliver more than the necessary efficiency and performance to satisfy DOCSIS requirements for CATV amplifiers. Consistent linearity is a primary requirement for reliable data transmission and signal integrity across HFC networks. The nonlinear behavior of active power devices can degrade the signal quality, leading to bit errors on digital channels and sometimes complete failure when trying to demodulate the signal.
Linearity of a gain block or amplifier depends primarily on these factors:
A high degree of linearity and efficiency are paramount when designing an HFC amplifier, and this is where GaN-based components have a clear advantage. Figure 2 shows the fundamental components of a CATV amplifier. In terms of linear output, the downstream performance of an HFC amplifier or node largely relies on the output stage gain block (also called the power doubler).
What is DOCSIS?
Data Over Cable Service Interface Specification (DOCSIS) is an international telecommunications standard that permits the addition of high-bandwidth data transfer to an existing cable television (CATV) system. It is used by many cable television operators to provide Internet access over their existing hybrid fiber-coaxial (HFC) infrastructure. The version numbers are sometimes prefixed with simply "D" instead of "DOCSIS" (e.g., D3 for DOCSIS 3).
Figure 2. Block diagram of a CATV amplifier.
GaN represents an enabling technology for power amplifier designs that can accommodate the demands of the DOCSIS 3.1 and DOCSIS 4.0 standards. Figure 3 illustrates a design stage that originally implemented the gain block architecture using field-effect transistors (FETs) based on GaAs technology. Replacing FET3 and FET4 with GaN-based components results in a substantial performance improvement because of the characteristics of these devices, including operation at high frequencies, high-voltage ruggedness, high current density, and power handling. GaN supports up to 10 W/mm compared to 1 W/mm for GaAs.
Figure 3. Gain block architecture improved through the use of GaN-based FETs.
Comparing the relative characteristics of material technologies used in CATV gain-block architecture, Figure 4 shows the advantages of GaN technology, enabling MSOs to boost linear output while maintaining existing amplifier spacing. This can minimize upgrade costs and make it possible to implement fiber deep solutions, locating fiber closer to the customer to enhance service and at the same time reducing or eliminating amplifiers.
Figure 4. Characteristics of GaN-based components compared to other options.
Two Qorvo products are outstanding design choices in this sector:
With the need for greater downstream bandwidth and increased upstream capacities spurred by DOCSIS 3.1 and DOCSIS4.0 standards, Qorvo can help MSOs respond to the challenge with GaN-based gain blocks for CATV signal amplification. CATV equipment manufacturers can rely on proven solutions that deliver better data transport using durable and reliable components.
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