Ampleon provides state-of-the-art RF power solutions for digital broadcast challenges

The broadcasting industry is in a period of fundamental change. In Europe, digital video broadcasting – second generation terrestrial (DVB-T2) transmitters continue to be rolled out. In the US, the Federal Communications Commission (FCC) has moved to address the looming spectrum crisis due to the arrival of 5G, launching a spectrum “repack” process, forcing many broadcasters to change transmission channels.At the same time, with the advent of the new standard ATSC-3.0, it is likely that a significant portion of these broadcasters will upgrade their transmitters while moving to new channels, addressing multiple changes at once, and

By Alan Hutton, Walter Sneijers, Herm Titulaer and Houssem Schuick

introduction

The broadcasting industry is in a period of fundamental change. In Europe, digital video broadcasting – second generation terrestrial (DVB-T2) transmitters continue to be rolled out. In the US, the Federal Communications Commission (FCC) has moved to address the looming spectrum crisis due to the arrival of 5G, launching a spectrum “repack” process, forcing many broadcasters to change transmission channels. At the same time, with the advent of the new standard ATSC-3.0, it is likely that a significant portion of these broadcasters will upgrade their transmitters while moving to new channels, addressing multiple changes at once, and Make sure their clients don’t have to redesign multiple times.

As 5G continues to roll out, other regions will also have to face the issue of spectrum allocation. These changes will drive the need for entirely new higher power and higher efficiency transmitters for many years to come. Radio frequency power amplifiers (RFPAs) are a critical component in signal transmission systems, as broadcast operators’ costs rely on high power amplifiers that can operate efficiently across the entire UHF broadcast spectrum.

This article will discuss in detail current market trends and explore the technical implications of these changes, as well as some of the challenges and available solutions for designers of high-power, high-efficiency RF power amplifier solutions for digital broadcasting.

The current state of the broadcasting industry

The three main factors currently driving the ongoing change in the global broadcasting industry include the continued rollout of DVB-T2, the advent of ATSC-3.0, and the “re-planning” of the TV spectrum in the US and elsewhere.

DVB-T2

The European Telecommunications Standards Institute has adopted a set of digital broadcasting standards. Released in 1997, the Digital Video Broadcasting – Terrestrial (Digital Video Broadcast CTerrestrial, DVB-T) specification was widely deployed around the world and drove the shutdown of analog broadcasting in many countries. As spectrum in Europe becomes increasingly scarce, DVB has released an updated DVB-T2 standard with higher spectral efficiency. By using Orthogonal Frequency Division Multiplexing (OFDM) modulation with a large number of subcarriers, DVB-T2 is a very flexible standard with the added advantage of being able to reuse existing antennas. Originally released in 2009, DVB-T2 was deployed in more than 12 countries by 2014, and market research firm Dataxis predicts that by 2022, 72 percent of European households will be able to transmit TV signals using the DVB-T2 standard.

ATSC-3.0

More recently, in January 2018, the Advanced Television Systems Committee (ATSC) released the ATSC 3.0 series of standards, which marked another important milestone in the evolution of television broadcasting systems. ATSC 3.0 contains about 20 standards and is designed to support some new technologies such as 120 frames per second, up to 2160p 4K resolution video channel HEVC, high dynamic range, Dolby AC-4 and MPEG-H 3D audio. ATSC 3.0 and DVB-T2 share many similarities, both use OFDM modulation and offer similar performance and flexibility. But DVB-T2 is already in widespread use, while ATSC-3.0 is just emerging today, and the first TVs capable of receiving ATSC-3.0 TV transmissions are expected in 2020.

Spectrum Replanning

In 2012, in anticipation of a future scarcity of valuable radio spectrum, the U.S. government authorized the Federal Communications Commission to encourage broadcasters to give up some of the spectrum. In the initial 470MHz ~ 860MHz broadcast spectrum, the high frequency band above 600MHz is already available for mobile wireless operators. At the same time, the launcher is ready for the new ATSC3.0 standard. To kick start the process, the FCC conducted its first auction, which ended in March 2017. As a result, 84 MHz of spectrum was freed up from channel 38 to channel 51, after which 70 MHz was sold to wireless operators in 10 MHz blocks. As the auction ends, the FCC estimates that about 1,200 stations will be affected by the process, with each station taking about three years to move into the new lower frequency bands. The overall spectrum re-planning has roughly 10 phases (see Figure 1), with staggered completion dates, with the aim of minimising disruption to broadcasters during the transition.

Ampleon provides state-of-the-art RF power solutions for digital broadcast challenges

Figure 1: The FCC’s spectrum replanning agenda. (Source: FCC)

Spectrum replanning will require many stations to change their transmission frequencies, which requires careful planning. If the TV station needs to transmit on two frequencies at the same time for a period of time, then a second transmitting antenna is required, which will have a knock-on effect on the signal transmission tower, other co-located antennas, HVAC and other systems. In many cases, broadcasters may find it more economical to replace existing transmitters, especially if the legacy transmitters are obsolete and cannot support ATSC-3.0 due to power or other constraints.

As operators have exhausted their frequency resources, the transition to DVB-T2 and ATSC-3.0 and the re-planning of spectrum from the current situation will lead to widespread replacement of TV transmission equipment in Europe, the US and the rest of the world.

Key Considerations for Power Amplifiers in TV Transmitters

A typical digital TV transmission chain consists of a transmitter, which consists of two basic components, an exciter and a radio frequency power amplifier (PA) (see Figure 2). The input to the system is the baseband signal through which the RF carrier is modulated in the exciter and then amplified by the RF RF Power Amplifier (PA) unit. The time-domain signal envelope of the modulated signal exhibits great variability in envelope peaks, compared to a constant average power level, the transmitter average output power (TPO) that determines the performance of a TV transmitter system. performance.

Ampleon provides state-of-the-art RF power solutions for digital broadcast challenges

Figure 2: A typical digital TV transmission setup. (Source: Ampleon)

Since their first introduction, RF transistors based on LDMOS (Laterally Diffused Metal Oxide semiconductor) have become the main solution for various power amplifiers, especially in the broadcasting industry. There are two different explanations for this fact, one is considering the high efficiency and high power advantages of the LDMOS process, and the second is the cost per unit power (dollars per watt), LDMOS-based transistors can provide a high Cost-effective solution.

A typical transmitter station provides 25kW of average RF power. This is accomplished by incorporating 4 or more amplifier trays (with multiple amplifiers), balanced driver stages, and preamplifiers in the transmit chain unit (see Figure 3). The advent of such high-power LDMOS RF transistors has facilitated a paradigm-shift in high-power amplifier performance over the past few years. From the early few hundred watts, we can now see RF components capable of handling more than 1.5kW of power. In fact, these transistors are fast becoming the best at meeting high-power and high-efficiency transmission, as well as extreme ruggedness standards in the RF industry.

Ampleon provides state-of-the-art RF power solutions for digital broadcast challenges

Figure 3: A typical power amplifier unit. (Source: Ampleon)


The advanced DVB-T2 and ATSC-3.0 standards use OFDM to modulate the signal, which affects every part of the transmission chain, especially the RF power amplifier, as it requires a peak-to-average ratio (PAR) of about 8dB higher to prevent power Saturation occurs in the amplifier, otherwise subcarrier intermodulation and out-of-band interference can occur. The above problems can be solved by reducing the backing-off power in the power amplifier, but this reduces efficiency, affects power consumption, directly affects power consumption and leads to higher operating costs.

Therefore, the challenge for RF power amplifier designers is to find the best balance of power and efficiency, and to design amplifiers that can achieve high efficiency under various operating conditions. Since many of the new transmitters deployed during spectrum replanning need to operate on the broadcaster’s previous frequencies before moving to the newly designated frequencies, RF power amplifiers must be able to operate efficiently at 470 MHz to 806 MHz. The entire UHF broadcast spectrum.

Current and Future RF Power Amplifier Solutions for DVB-T2 and ATSC-3.0

Two relatively recent advances in RF power amplifier technology are helping designers to more easily accomplish their design tasks: the proven high-efficiency ultra-wideband Doherty (UWD) architecture, both symmetric and asymmetric, and a new generation of high-power LDMOS transistors, which offer unprecedented robustness and best-in-class gain and efficiency.

As a key global provider of power solutions to the broadcast industry, Ampleon has invested significant resources in developing UWD reference designs. These solutions demonstrate how the BLF888 (see Figure 4) can deliver 150W of average DVB-T power over the entire spectrum from 470 to 700 MHz. The BLF888 transistor family has been so successful in the market that many broadcast equipment manufacturers are using these devices in their TV transmitter solutions in preparation for the demands of the U.S. “Re-Spectrum” program and the introduction of the ATSC-3.0 standard.

Ampleon provides state-of-the-art RF power solutions for digital broadcast challenges

Figure 4: Ultra-wideband Doherty designed with BLF888E. (Source: Ampleon)

Based on the market success of the BLF888 and market expectations for future demand for higher power and higher efficiency, Ampleon has recently introduced its next generation broadcast amplifier products, the BLF989 and BLF989E RF power amplifiers. Among them, the BLF989 can achieve the highest narrowband efficiency of up to 55% under DVB-T8K OFDM signals, and the extreme average power level of each transistor is 200W (950 W peak), covering the 470MHz ~ 494MHz range. The BLF989E (see Figure 5) can provide an average power of 180W, with a typical efficiency of 50%, and can cover an ultra-wide frequency band of 470MHz to 620MHz.

Ampleon provides state-of-the-art RF power solutions for digital broadcast challenges

Figure 5: UWB Doherty with BLF989E (Source: Ampleon)

The BLF989E efficiency and power versus frequency curves (see Figure 6) demonstrate how the highest UWD efficiency can be achieved through a special a-symmetrical Doherty structural design. These new UWD high-efficiency amplifier solutions represent the most cost-effective broadcast RF power amplifiers on the market today. Through ingenious innovations, maximum efficiency, bandwidth and reliability are ensured.

Ampleon provides state-of-the-art RF power solutions for digital broadcast challenges

Figure 6: BLF989E efficiency and power versus frequency. (Source: Ampleon)

in conclusion

The introduction of DVB-T2, the emergence of ATSC-3.0 and the re-planning of the spectrum required broadcasters to upgrade their equipment systems, which provided huge business opportunities for TV signal transmission equipment manufacturers. This market will continue to grow as various regions of the world have to address the spectrum scarcity issues that arise. The advanced modulation schemes used by DVB-T2 and ATSC-3.0, such as OFDM, present particular challenges to the design of RF power amplifiers, as higher power and higher efficiency must be balanced across the UHF broadcast spectrum. Recent advances in power LDMOS transistors and UWD architectures are addressing these challenges. Market demand for higher power and efficiency is not expected to diminish anytime soon, and disruptive trends in the broadcast market will continue to drive the LDMOS price/performance curve without sacrificing quality. As the world’s leading manufacturer of power transistors for the broadcast industry, Ampleon is fully positioned to support partners in the broadcast industry ecosystem. Ampleon’s flagship BLF888 series transistors have already played an important role in providing a wide range of solutions for the industry, and the BLF989 and BLF989E represent the roadmap for the future in the face of the ever-evolving market demand for higher power and higher efficiency.

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