Post a Comment
Feature
Global Report 3: Globalization and analog
Analog is the real world, and needs differ from place to place. Accordingly, analog engineers face challenges in accounting for a multiplicity of standards, conventions, and consumer preferences, depending on where a product finds use.
By Paul Rako, Technical Editor -- EDN, 11/9/2006
|
Cell phones operate on four frequencies and have both analog and digital protocols, and many frequency and modulation standards exist for wireless and phone protocols (Reference 1). Analog designers rose to the challenge with triband or even quadband phones that work in many areas. "One of the big challenges in designing wireless products for global markets relates to the regional differences in frequency allocations," says Doug Grant, director of business development, RF, and wireless systems at Analog Devices. "For example, the frequency bands for the GSM [Global System for Mobile communications] cellular system in North America are 850 and 1900 MHz, whereas, in the rest of the world, they are 900 and 1800 MHz. The bands are far enough apart that [manufacturers have to optimize] matching networks for each of the four bands." He also notes that, when developers were first contemplating 3G cellular, they hoped that a single air interface for use in a limited number of bands would emerge. "Somehow, over time, we've lost the U in UMTS [Universal Mobile Telecommunications System] and have multiple air interfaces and multiple frequency bands. In other applications, such as short-range, unlicensed wireless links, the frequency allocations differ, and the specs for transmitter-signal purity vary widely because different services are in the adjacent bands in each region," he says.
Hardware engineers have also come to the aid of consumers when manufacturers have patented protocols, such as CD-R, CD+R, and the rewritable DVD formats. Engineers simply created drives that would support all the formats. The high-definition-DVD conflict will be even more difficult, because the HD-DVD and Blu-ray camps are vying for dominance, and China announced it would conform to neither standard and issued a proposal for a disk based on its EVD (enhanced-versatile-disc) standard. Once the bits on a DVD get past the read channel, digital engineers all have similar jobs. Analog engineers, on the other hand, must provide the laser drivers, the read-channel signal chain, and the servo system to track the disk as those digital bits come pouring out.
Analog designers also face issues of global regulatory compliance. In the United States, they must comply with the UL (Underwriters Laboratories) listing, and, in Europe, they must comply with the CE (Conformité Européenne) standard. FCC (Federal Communications Commission) standards determine RFI/EMI (radio-frequency-interference/electromagnetic-interference) emissions in the United States. In Europe, CE details not only RF emissions but also RF immunity. These immunity standards have proved more challenging than the emissions standards for engineers to meet. The Crown Audio Web site lists the following CE standards that its products are subject to for US and Canadian standards. Crown also must comply with worldwide standard if they want to sell their products internationally (Reference 2).
- EN 55103-1: 1995 Electromagnetic Compatibility Product Family Standard for Audio, Video, Audio-Visual, and Entertainment Lighting Control Apparatus for Professional Use, Part 1: Emissions;
- EN 61000-3-2: 1995+A14: 2000 Limits for Harmonic Current Emissions (equipment input current ≤16A per phase);
- EN 61000-3-3: 1995 Limitation of Voltage Fluctuations and Flicker in Low-Voltage Supply Systems Rated Current ≤16A;
- EN 55103-2: 1996 Electromagnetic Compatibility Product Family Standard for Audio, Video, Audio-Visual, and Entertainment Lighting Control Apparatus for Professional Use, Part 2: Immunity;
- EN 61000-4-2: 1995 Electrostatic Discharge Immunity (Environment E2-Criteria B, 4 kV Contact, 8 kV Air Discharge); and
- EN 60065: 1998 Safety Requirements Audio Video and Similar Electronic Apparatus.
To illustrate just how complex it can be for analog designers to span these differences, consider something really simple, such as plugging a device into an outlet: Even this task can be daunting for an analog engineer.
Power globalizationOne obvious problem that analog engineers face is the diversity of ac-power standards. The US Department of Commerce publishes the 30-pg Electric Current Abroad (Figure 1), which details not only worldwide voltage and frequencies of ac power, but also the plugs and receptacles in use (Reference 3). The IBM division that sells its mainframe-computer power front end to industrial customers offers an internal document that shows the power quality of the ac power in all countries. The spikes, sags, and frequency variations can be even more difficult to design for. A universal supply is universal in name only if it can operate from 90 to 240V on 50 or 60 cycles. That supply must also withstand the stresses of surges and spikes. A savvy designer also must understand that many countries often experience dropouts of two or even five cycles, so designers must use higher value input-holdup capacitors than they would normally use.
"To compete in the global market, today's analog ICs must address a wide range of application and voltage requirements," says Doug Bailey, vice president of marketing for Power Integrations. "For example, we know that Japan's ac main can be as low as 90V power, whereas Europe uses 240V. At first blush, this information seems like enough to design a power supply that will operate worldwide. The reality is more difficult. In India, the power grid is unreliable, forcing many big electricity consumers to use private generators during outages. When the power goes down, and the generators switch in, numerous line spikes occur. When the power grid comes back up, everyone's using generators. The power grid is unloaded, so the voltage can overshoot and ring for several minutes. The resulting surges can go as high as 400V. Products have to be able to handle these extremes, so our application circuits must cover ultrawide ranges of voltage and help ensure that our chips withstand the spikes."
Besides fundamental voltage differences, analog-system designers must consider regulatory differences on power supplies. In Europe, the IEC (International Electrotechnical Commission) standard 61000-3-2 took effect in 2001. China and Japan have adopted similar legislation. This standard applies to power supplies of more than 75W. In those cases, the law prevents creating input harmonics over a small level. This requirement effectively mandates a power-factor-correction circuit. In a conventional line-power-supply front end, once the capacitor charges up at turn-on, the only current that flows into the capacitor is at the peak of the input-voltage waveform (Figure 2). These current spikes mean that the input current does not track the input voltage—that is, the input current is not a sine wave. For countries that mandate low input harmonics, the supply has to use a power-factor-correction front end (Figure 3). This configuration uses a boost topology that uses the input-sine-wave voltage as a reference for the input current. This reference results in a dc-output voltage about twice the peak input but ensures that few harmonics inject themselves back into the power gird.
Harmonic regulations represent just one aspect of worldwide power regulations. A global designer must take into account many other standards, such as the US Energy Star program for computers, and regulations that limit the amount of standby power that remote-control circuits, such as IR detectors, use. In California, the cost of electric power is about $1/W for a device that runs 24 hours a day, seven days a week, all year. If your house has many standby remote-control circuits, it may cost more than $100/year just to keep them on and ready for your command. Several jurisdictions around the world are acting to limit the amount of power standby circuits use. Power Integrations has a table of them on its Web site under "Green Solutions/Regulations" (Reference 4).
Globalization presents challenges to other aspects of power supplies besides ac power. Global markets have needs that will require special features in handheld products, such as cell phones and MP3 players. A standard reference design will provide for the powering of a base system. But if a market requires multiple cameras or colored-LED lighting that flashes in time with music, then the power system will become far more complex. In addition, some countries may have requirements that dictate the use of certain battery chemistries.
"As far as globalization's effect on our customer's power requirements, there is less of an impact for the handheld-system market," says Roger Woodward, western regional sales manager at Summit Microelectronics. "The battery for a portable player or cell phone is the same in Japan as it is in the United States or in India. We do see an impact on the local market requirements for features. When a market demands more features, that demand requires specialized power chips." He says that one benefit of digitally controlled analog-power systems is that they build programmability and control of the power system into the chip.
|
Summit does not develop digital-power chips in the sense of using a DSP to control the loop. "Our customers make handheld, battery-powered products. The first question they ask is: 'How high is the quiescent current?' If we told them anything more than 50 μA, they would not even want to see a data sheet and would not ask us back," says Abid Hussain, Summit Microelectronics' director of marketing. "We cannot have a DSP closing the loop and drawing milliamperes of power. That is why we discourage the term 'digital power' in reference to our products. We prefer 'digitally controlled analog.'"
Telecom globalizationSome uniformity does exist in the requirements of the POTS (plain-old-telephone system), at least in how the equipment works. Regulatory standards that the phone equipment must comply with vary from country to country, however. No one knows this fact better than the designers at Silicon Labs. Many years ago, they set out to design a modem that would comply with every standard in the world. Thus, they created the Isomodem line of chips. The name of one system block of all modems, the DAA (direct-access arrangement), provides a clue to the challenges that designers face. The chips must ultimately interface with the real-world twisted-pair wiring, which can encounter lightning strikes and line-cross events. A line cross occurs when the electric power that is running on the same utility poles as the telephone lines breaks and falls across the phone line. In some regions of the United States, those utility poles carry 440V-ac power, and peak voltage is more than 600V. European lines, on the other hand, directly distribute 240V. Nevertheless, the standards for the line-cross event differ all over the world. In the United States, FCC Part 68 specifies the design limits and testing and requires surge testing at 1500V. In Europe, European standard EN55024 specifies the limits and does testing at 1000V. Real-world conditions are even more demanding: A line-cross event may generate only a few hundred volts on a phone line, but a lightning strike can generate far more voltage, and the rise time of that event will be short. Designers at Silicon Labs have seen field voltages of 4500V.
Jim Judkins, marketing manager at Silicon Laboratories, points out that flexibility is key. "Our Isomodem has to work in 100 countries," he says. "About half of those have requirements similar to FCC Part 68. Other countries seem more interested in providing barriers to entry to their markets rather than a reasonable standard. The Isomodem has 40 registers to tailor its performance for all these disparate markets. We can vary dc termination, ac impedance, ringer impedance, and many other analog parameters." Digital control and supervision of analog functions provide flexibility, just as Summit Microsystems uses digital control over analog-power functions to achieve flexibility in that realm. Judkins says the company's customers must use the application staff to ensure that they are properly designing the part into the target system. In addition to the applications group, he points out, the company also has a compliance-engineering group, which ensures that customers understand all the regulatory requirements that countries place on the product.
The ability to break a large project into many pieces that engineers worldwide can work on is the driving force behind object-oriented design, as well as digital design. Designers cannot partition analog designs in this manner. They must be privy to the needs and architecture of the entire system. All analog parameters interact, meaning that they more severely feel the effects of the real-world requirements that globalization presents. Fortunately, innovative analog companies are meeting these challenges. The challenge of design for a global marketplace is just another requirement for analog designers, along with cost, thermal effects, size, speed, and time to market. With the advent of new, exciting space programs, the opportunities for analog will be out of this world.
| For more information | ||
| Analog Devices: www.analog.com | Crown Audio: www.crownaudio.com/amp_htm/certifmarks/certifmarks.htm | IBM: www.ibm.com |
| Power Integrations: www.powerint.com | Silicon Laboratories: www.silabs.com | Summit Microelectronics: www.summitmicro.com |
| Summit Microsystems: www.sumicro.com | ||
| Author Information |
| You can reach Technical Editor Paul Rako at 1-408-745-1994 and paul.rako@reedbusiness.com. |
| References |
|
