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TV Evolution Breeds Business For GaAs Chip Manufacturers

Advances in television broadcasting, such as interactive services and the delivery of high-definition content, are generating demand for higher bandwidth cable-television networks. This evolution of the medium is driving an increase in shipments of gallium arsenide components, according to two leading RF chip manufacturers. Richard Stevenson investigates.
Revenue from gallium arsenide (GaAs)-based content deployed in cable television (CATV) infrastructure is set to rise from $20 million in 2004 to $47 million in 2009, according to market analyst Asif Anwar of Strategy Analytics. Anwar believes that this growth will come from increased sales of higher-bandwidth amplifiers used to deliver digital and high-definition TV formats.



This optimistic outlook is shared by Ron Michels, Anadigics vice-president of broadband products. Michels - who claims that Anadigics is the leading manufacturer of GaAs components for CATV infrastructure and for set-top boxes that convert cable broadcasts into signals suitable for TV inputs - believes that increased sales of advanced set-top boxes will also boost the company s revenue. He says that these latest-generation components require additional GaAs for functions such as viewing one channel while recording another.
Solid growth

According to Michels, roughly one-third of Anadigics revenue comes from the CATV sector. In fiscal 2004 this sector equated to about $30 million. Sales of CATV-related revenue experienced double-digit growth last year, and Michels expects "solid" business from this sector for the next three to four years. He predicts that Anadigics infrastructure business will maintain healthy revenues, but this will be overshadowed by sales growth of GaAs chips used in set-top boxes, figures that are not included in Anwar s report.


Michel explains that Anadigics components are used throughout the CATV network. At the "headend", where the broadcast originates, they amplify the transmitted RF signal that is then converted into optical signals transmitted to a local hub; in the 75 Ω, 0.25 inch-thick coaxial cable that connects the hub to the home they are used to boost the signal; and in the set-top boxes they are used as tuners to select the different channels available.



Anadigics CATV unit shipments are dominated by chipsets for set-top boxes (2 million per month), followed by infrastructure components (100,000 per month). Amplifiers for the headend represent the smallest sector of the business, contributing sales of only 5000 components per month.


Chipsets are sold by Anadigics for use as integrated tuners in set-top boxes. "Anadigics is the leading supplier for CATV applications specifically for set-top boxes," said Michels. The company has been shipping a module with an up converter and a down converter on separate packages, because when the product was developed it was not possible to deliver an adequate performance from a single package.
Integrated processing

However, Anadigics has just released an integrated tuner in a 6 x 6 x 1 mm package, containing a GaAs and a CMOS chip. "The combination of using GaAs on the front end of the tuner and CMOS for the rest of it gives us a cost-effective, small die area, even though it uses two chips," remarked Michels. The tuner was produced using a derivative of the company s integrated HBT and PHEMT process, which allows production of both transistor types on the same InGaP/GaAs die (see Compound Semiconductor June p6). The hybrid chip faces competition from all-silicon tuners, but Michels thinks that Anadigics product will triumph due to its lower noise.


Anadigics also manufactures GaAs-based active splitters for set-top boxes, which separate the RF signal coming into the set-top box into two or three different outputs. Active splitters are a pre-requisite for the growing market of advanced set-top boxes that contain hard drives. These boxes allow viewers advanced digital functions such as displaying two programs on screen simultaneously, rewinding and pausing live TV, and recording one channel while watching another.



"You have all sorts of silicon manufacturers trying to compete with us for active line splitters, but nobody has been able to come close," boasted Michels. He believes GaAs splitters have a significant advantage over their silicon counterparts in terms of linearity, and are better suited to the wide bandwidths needed to deal with several hundred separate channels. Michels adds that when the signals are split into two, 3 dB of power is lost. If no action is taken to compensate for this loss, he explains, then there is a 3 dB increase in noise: "Again, the low noise [associated with] GaAs is the key here, both on the infrastructure side and in the set-top box."


According to Michels, it is the increasing popularity of advanced set-top boxes that are boosting Anadigics revenue. As the splitter is located at the front end of the set-top box, separate tuners are required for each line after the incoming signal is split. So, for a typical tuner, there could be one splitter, two tuners each containing two separate chips, and occasionally a reverse amplifier that is used to send information back to the headend so that viewers can access interactive services. "That s [up to] six GaAs parts in many of the boxes that are being shipped by Anadigics," said Michels, although he adds that the company is seeing a decline in reverse-amplifier sales.
GaAs beats silicon for noise

Another function of the various splitters and tuners is to amplify the RF signal, says Michels. Although the splitters provide only 4-5 dB of gain, integrated tuners can contribute a further 35 dB. Michels says that this amplification is needed primarily to cater for the large dynamic range of the signal levels entering the box. Gain is only required when the signal is low, which occurs when the distance between the set-top box and the final amplification stage of the CATV broadcast is relatively large.



Anadigics also sells products for CATV infrastructure, such as line amplifiers, to what it describes as the leading supplier of CATV infrastructure and 25-30 second-tier suppliers. These line amplifiers operate over the 50-870 MHz frequency span. The upper end is expected to be extended to 1 GHz to increase the available bandwidth.


Although the upper end of this frequency range is comparable to frequencies used in cellular communications, the amplification requirements are remarkably different. Line amplifiers for CATV infrastructure plug into a mains transformer, and so, unlike mobile-phone power amplifiers, little effort is directed toward improving operating efficiencies. However, CATV amplifiers have to deal with hundreds of different channels, and must deliver uniform gain over a broad bandwidth to within a few tenths of one decibel. Line amplifiers must also have low noise levels, because passing several hundred video channels simultaneously through an amplifier can create cross-modulation distortion.


The number of amplifiers installed between hub and home depends on the transmission distance and the number of customers. If the local network serves only 100 homes, then amplification may not be necessary, but most cable systems transmit to 1000-2000 homes, which means that several amplifiers are needed.
GaAs offers more reliability

Aside from greater linearity and lower noise, Michels claims that GaAs amplifiers also offer greater reliability. This is important for its customers because supporting cable networks with only slightly higher failure rates is considerably more expensive.


Another line-amplifier manufacturer is Motorola spin-off Freescale - which targets a small part of its business at CATV. Scott Craft, Freescale s product manger for CATV in the RF division, says that the company produces hybrid and IC amplifiers for infrastructure applications.


Hybrid amplifiers are driving sales of GaAs components at Freescale. Craft said: "If we look at 2004, the year-on-year increase in GaAs was up 86%, but silicon bipolar was basically flat. The relative share has moved from silicon to GaAs. I would say that, worldwide, more than half of hybrid amplifiers use GaAs right now. That s increasing, and will continue to increase."


Craft identifies lower distortion as the primary advantage offered by GaAs amplifiers over their silicon-bipolar rivals. This characteristic allows transmission of stronger signals, resulting in lower noise and access to a greater dynamic range. "The higher output capability means that you can space your amplifiers further apart, and that has a direct relationship with system cost," explained Craft.


The transition from analog to digital CATV transmission is yet to have a dramatic impact on amplifier requirements, says Craft, because today amplifiers have to support both broadcast formats.


Craft thinks that the CATV market will expand quickly over the next few years as the network bandwidth grows and transmission is extended to around 1 GHz. "I see CATV going into other countries, but I think you have to be very cautious there," remarked Craft, who adds that in developing countries CATV may never be rolled out, because there are now many options for broadband transmission networks available that did not exist 10 years ago.


Craft believes that broader bandwidth amplifiers will start replacing existing line amplifiers so that CATV networks can keep pace with the fiber-to-the-home systems now being deployed. This upgrade to 1 GHz offers a straightforward way to add more channels, says Craft, who expects steady growth in the GaAs amplifier business. "The overall market for this type of amplifier will grow over the next five years, but it will not be dramatic growth. It will grow for five, maybe 10 years, but will decline further out."


One of the long-term issues with cable, explains Craft, is the significant attenuation of the RF signal at frequencies above 2 GHz, which would limit the number of TV channels that CATV can transmit. However, he points out that an all-digital network will allow more channels. If the network operated at frequencies of up to 1 GHz, then with suitable compression 900 channels could be transmitted. That would give viewers a staggering choice of TV channels, although some viewers would have to upgrade their set-top boxes to receive the new transmissions.


Another US chip maker producing components for CATV is Sirenza Microdevices. According to Dan Wilmot, Sirenza s director of new business development, the firm s CATV business, which is dominated by silicon products, accounts for 3-5% of revenue.


The company is now producing amplifiers and receivers for the return path to the headend. This path, which gives viewers access to TV-channel guides and allows authorization of pay-per-view content, uses dedicated channels operating at around 80 MHz. Wilmot believes that at these frequencies silicon offers a better performance than GaAs, which can require the addition of bandpass filters to operate in this frequency domain.


Wilmot also believes that the linearity of silicon is good enough for line amplifiers operating at frequencies of up to 1 GHz. "Silicon is sufficiently linear," claimed Wilmot, who disagrees with Michels of Anadigics, and estimates that more than 80% of today s line amplifiers use silicon: "I m not [aware of] the transition to GaAs myself, but maybe there s something under the radar that I m not seeing."



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