Monthly Archives: January 2016

Digital technology will govern power control

Digital technology will be the focus for power control in the 1990s. Digital control is nearly twice as efficient as linear control and offers savings in size and weight of end products. Transformers required for linear control are practically eliminated in digitally controlled off-line switchmode supplies.

Digital control of brushless motors is much more efficient than linear control. Integration of a control IC and a MOS power transistor on a single chip, called ‘smart power’, could lead to the development of a complete switchmode power supply on one chip by the end of the decade. High-voltage ICs will bring about major changes in components such as motors, relays and sensors that have remained unchanged for years. The 1990s will see the development of smarter electrical products, such as electrical outlet boxes in homes that can be programmed from a central computer, and household products with built-in temperature sensors to prevent dangerous heat levels.

Power control in the 1990s will see design emphasis shift decidedly from linear to digital technology. One reason is that digital control of power devices is about twice as efficient as linear. Second, digital techniques allow for a tremendous reduction in the size and weight of the end product. By the end of the decade, digital control will dominate–just a few isolated linear applications will remain.

Digital technology impacts power-supply design and load control. For example, the big, heavy step-down transformers required by linear supplies can be virtually eliminated in off-line switchmode supplies under digital control. A 100-W supply that fits into a desktop PC would be impossible to build using linear technology. Beyond switchmode supplies, IC technology can power chips directly from the ac line.

Control of brushless motors is made more efficient by digitally switching the motor voltage on and off rather than varying it linearly. Digital control also can result in a dc-variable stepwise approximation to a sinewave. Varying the power to any kind of load is more efficient than applying a steady ac voltage. Ample savings in system power consumption can be achieved by applying one level of power to actuate a relay or solenoid, and then reducing the power to hold it. With less power, the voltage to the device can be increased above its rating, enabling faster operation. This can increase the productivity of machinery without adding capital investment.

An idea that’s taking hold is the integration of a control IC and MOS power transistor on one chip, a concept now called “smart power.” By the end of the 1990s, smart power will probably lead to a complete switchmode power supply contained in one IC.

At low voltage–up to about 60 V–a smart-power IC is more cost effective than an IC plus a discrete power transistor. A perfect example in bipolar technology is one of the original smart-power devices called a three-terminal regulator.

To operate at higher voltages (200 V and more), you need a mixed process–an MOS output with either a bipolar or CMOS input. Up to now, it wasn’t easy to build these smart-power structures. You need large silicon areas to isolate high- and low-voltage devices and you must use IC processing, which is more expensive than discrete processing. Moreover, you can’t use some of the processing tricks with ICs that can be employed in discrete processing.

At Power Integrations, we’ve developed a high-voltage processing technology that overcomes the aforementioned problems. We can build a high-voltage smart-power IC using the same processing steps that are utilized in a conventional IC, and the integrated power transistor is not larger than an equivalent discrete. This process finally makes high-voltage ICs for power control practical.

With this advanced high-voltage process, designers can control power directly from the ac line without the need to step-down the voltage in the power section. One such application is in stepper-motor drives, which currently require a 40-V power supply that’s larger than the motor and its controller combined. The process eliminates that supply by allowing the stepper to be powered straight from the ac line voltages. A PC that controls a burglar-alarm system can also be considered. Designers can now get an IC that links directly from the wall outlet’s 120-V ac to the computer’s 5-V dc control logic.

Historically, new markets are created by each new innovation in semiconductors: transistors were responsible for compact radios and audio products, and microprocessors brought about the age of computing. High-voltage ICs will revolutionize the way we think about the electro-mechanical world. Such components as motors, relays, and sensors have remained the same over the years, but applying modern electronics to them will create major changes.

As we proceed into the 1990s, we’ll see smarter electrical products. For example, electrical outlet boxes in future smart homes will be programmable from a central computer. Not only will they turn on appliances and lighting fixtures, but they’ll have built-in intelligence to protect themselves against unsafe power drains from appliances. Temperature sensors will be built into common products, such as cooking utensils, to protect them from dangerous heat levels that could cause a fire. Using digital techniques to control power will lead to many innovations that we haven’t yet thought about.

Increased complexity in computers will breed advanced equipment

Widely available computing power will both create and solve problems in the 1990s. Testing problems will be created by the increasingly complex chip and board designs that computer power makes possible, but new types of computer-based test equipment will be developed to solve these problems. Test equipment for both software and hardware will see great advances due to increased computing power.

The trend toward modular designs for electronic components will be accelerated as improvements in test equipment ease the burden of testing modular components. Current ASIC verification equipment that compares results achieved in simulation with results achieved in tests of the real device and highlights differences will serve as a model for new test systems for assembled circuit boards. This equipment will allow engineers to design massively complex systems that were inconceivable before because of the impossibility of testing them. The test environment in the 1990s will see built-in self-test and external test equipment working in conjunction to improve the overall performance of electronic components.

The next decade will see the influence of the computer reach new plateaus: Every aspect of electronic engineering, from the first stages of design, through manufacturing, final test, and field service will be affected. The widespread availability of computing power will create and solve difficult problems. It will create testing problems with the increased complexity of chips and boards that can be designed. Consequently, new types of application-focused test equipment to analyze the chips and boards will arrive, which use computing power and communications to combat these obstacles.

More computing power will also forge great improvements in software test equipment. The equipment will include instruments to functionally verify software, measure software performance, and determine whether it was fully and correctly executed.

This software test equipment will be closely coupled to the new test equipment for hardware. Single measurement platforms will analyze any characteristic of an electronic system, from the analog characteristics to microprocessor and software analysis. This will be a true “test station,” which will be used in conjunction with the “workstations” of the future to supply a consistent design and test environment.

One consequence of these improvements will be an acceleration of the design modularity trend for almost all electronic systems. Modular design is attractive because engineers can quickly develop extremely well-focused products. But it puts a heavy burden on test engineers to ensure that software and hardware modules work properly in all of their intended environments and combinations. For example, if your product is a plug-in board for the IBM PC/AT, you want to ensure that it will work in every PC/AT that IBM has shipped and in the boxes they will produce in the future. Improvements in test equipment will ease that testing job and thus encourage this focus on modularity.

Current ASIC verification test equipment gives us a glimpse of what the future holds in this area. Such equipment is linked to a design system, from which it gains access to the test vectors that were applied to the ASIC during the simulation phase of the design process. It applies those vectors to the real device during test, compares the actual results with the simulated results, and highlights any differences.

In the ’90s, that same approach will be applied to assembled circuit boards, which are even more complex than ASICs because they can hold from 6 to 20 complex ICs. Design equipment capable of full board-level simulations will be widely available, and links will be supplied between board testers and design. As a result, engineers will be free to design systems of enormous complexity–systems that previously were unthinkable because they would have been impossible to test.

Most electronic products will have some built-in self-test circuitry that can verify the equipment’s functionality but can’t make reliable time-domain measurements. External test instrumentation will always be needed to ensure that the equipment meets system specifications.

In fact, built-in self test and instrumentation will work together in the next decade. Diagnostic techniques, such as boundary scan, will give rise to test equipment that can clock the preset values into a circuit and record the outputs of the scan circuitry. This will enable rapid scan-test development, and make it possible for circuit defects to be quickly isolated.

This same instrumentation will also measure the timing margin of the circuit under test to ensure that an electronic module will work in all of the intended environments. In future manufacturing facilities, continuous tracking of the timing margins will offer an early warning of system problems, which could shut down a production line. If the system timing margins are deteriorating, individual component performance can be checked and the cause determined, while the systems are still meeting specifications.

Meeting all specifications is one measure of quality that American electronics companies are striving to achieve. Tektronix and its customers are trying to make sure that our verification of performance is rigorous–that every function in a complex IC works, that every branch of a program executes correctly, and that plug-in boards function at every clock speed it may encounter.

ASIC and FET innovations will dominate power device technology

Innovations in power devices in the 1990s will be in the areas of power application-specific integrated circuits (ASICs) and cost-effective, high-voltage field effect transistors (FETs) with low on-state resistance. Power ASICs will make it possible to integrate solid state relays (SSRs) with temperature sensors, or to put special timing or decision-making logic on an SSR.

FETS will be used in devices where standard SSRs cannot be used because of a lack of room for a heat sink or other cooling device. They will also be used wherever power dissipation is a major concern. The 1990s will also see the development of closer relationships between designers and device suppliers, opening a way to solving a number of long-standing performance problems.

As a manufacturer of solid-state and time-delay relays, the most important technological innovations I expect to see in the ’90s will be in the areas of ASICs and FETs. Innovations in ASICs will enable us to do things we couldn’t do before, and FET innovations will make it possible for our devices to fit into areas that were previously closed to solid-state power switches.

Equally important will be the benefits that designers will realize from the closer relationships they must develop with their device suppliers. This trend can be seen throughout the industry as electronic technology becomes more complex–and more potent. Unless designers develop these relationships, much of the available technology may not translate into products that help solve their design problems.

As power ASICs become a reality–that is, as it becomes possible to develop semiconductor devices for specific power applications at acceptable cost–manufacturers similar to ourselves will be able to offer functions that previously were never considered. For example, if a maker of heat pumps typically uses solid-state relays (SSRs) in combination with temperature sensors, we could possibly combine the two into one device, integrating a temperature sensor into an SSR. Or we could put special timing or decision-making logic into an SSR, if it seems to be sensible.

The question is: How are we going to know whether that’s a sensible thing to do? And if it is, how are we to know exactly what type of timing or decision-making circuitry to include?

There’s only one source for that information–the design engineers who use our products. Unfortunately, those designers aren’t in the habit of discussing the details of their designs with component manufacturers. The traditional way of buying power switching devices, such as SSRs, is to choose them from a catalog. Rarely do designers sit down with a relay manufacturer to discuss how, where, and why they’re using that manufacturer’s products. Yet, unless designers start doing that, the full benefits of power ASIC technology will go unrealized.

What sort of device improvements might come out of such improved communication? One improvement is a means for dealing with a common objection to the use of SSRs–when they fail, they fail closed. Users would prefer that they fail open and leave their loads unenergized.

It’s possible to build circuitry into an SSR to detect when the output switch has failed. Such circuitry would compare the state of the output with the state of the input. Then, if there were an output without an input, the circuitry would give a failure indication and also open a particular one-shot electromechanical device say, a fuse, to shut the system down. The details are less important at this point than the fact that until now, such devices would have been too large and too costly to be worth serious consideration. Now we know that they can be made small enough, and we’re fairly sure they’ll be economical in next few years.

I look forward to the advent of the cost-effective, high-voltage FET with a low on-state resistance. Presently, typical SSRs that switch ac loads utilize thyristors as their switching elements. Those devices, whether they’re back-to-back SCRs or triacs, typically have an on-state drop of 1.0 to 1.5 V, which means they dissipate some 20 to 30 W with even a moderate 20-A load.

A thermal load of 20 to 30 W can’t be ignored and requires either a heat sink or some form of cooling. The need to dissipate significant power militates against using SSRs in many applications where there simply isn’t enough room for a heat sink or other cooling apparatus.

Today, high blocking voltage and low on-state resistance are almost a contradiction in terms for FETs–at least at affordable prices. Nevertheless, I believe that high-voltage FETs with very low on-state resistances–a few milliohms–will become available at acceptable prices during the 90s, making it possible to build high-voltage, high-current SSRs that dissipate very little power.

Those relays will be used in close quarters where SSRs can’t be used today. In addition, designers will prefer them over today’s devices even in applications where there’s sufficient room for proper cooling, simply because it’s always a good idea to minimize power dissipation.

But, in my opinion, the interesting effects of technological change in my area of interest in the ’90s will be on “how” we do business with each other, rather than on the details of “what” we do.

Semi device technology will drive connections at all levels

Advances in semiconductor technology will drive interconnect technology developments at all levels, from device to network. Performance improvements in systems require high-speed connections to be treated as transmission lines. At the device level, the trend toward the small, dense interconnects of the multichip module will continue. At board level, transmission-line techniques will be used for interconnection of high-speed logic cards. The backplane will survive, but connectors will be microstrip, stripline and coaxial structures that reduce noise and speed signal flow.

Surface-mounting will be the dominant component mounting technology. Transmission-line techniques will also be used at the subsystem level to respond to increased IC and system speeds. Plastic optical fiber will be popular for applications requiring increased bandwidth, and optical cable and multiplexing will play an important part in tomorrow’s smart home, which will be bus-wired, microprocessor-controlled, and have a wide variety of programmable electronic devices.

Advances in semiconductor technology will form the driving force for all of the important interconnect technology developments from the device level to the network level. For example, at the device level, there’s the multichip module with its small and dense interconnects between chips playing a major role in systems, a trend that will continue during the 1990s. Designers will perform trade-off analysis in deciding between using an ASIC and a multichip module for circuits of the same complexity. By the end of the 1990s, ASICs packaged in multichip modules to form specialized systems on a substrate will be commonplace.

At AMP Inc., we have a system called the Microinterposer under design for connecting planar substrates with a pressure surface-mounted technique. We no longer think of these links as simply rows of ohmic contacts. The performance improvements in systems dictate that all of the high-speed connections be treated as transmission lines.

At the board-to-board level, today’s backplane will continue to survive. But the multiple-pin connectors can no longer be simply pins in a plastic housing. Transmission-line techniques must be used to interconnect high-speed logic cards. Connectors will be stripline, microstrip, and coaxial structures designed to speed signal flow and reduce noise. Today’s pin fields aren’t most efficient in moving signals, power, and ground around a system.

There’s no doubt that surface mounting will become the primary technology for component mounting. For many connections, efforts are already underway to eliminate through-holes. Smaller center lines will lead to surface-mounted backplane connectors that use pressure connections rather than solder. Similar techniques will be used for other connector types. On the other hand, some connectors for some applications will stubbornly retain their strong links to the older through hole technology well into the ’90s.

At the subsystem level (for example, connecting a disk drive to its controller card or a power supply to its loads), advanced technology will play a major role. Here again, transmission-line techniques will be needed to keep pace with advances in IC and system speeds.

Plastic optical fiber for short links with system enclosures will gain in popularity for applications that require increased bandwidth. Inexpensive plastic optical cable will be a candidate to replace copper cable in a wide variety of subsystem (wire-harness) interconnect applications. Today, it’s difficult to consider optical fiber for short links in a high-speed system. One reason is that a time-delay penalty must be paid going between the optical and electrical domains. Considering propagation delay only, an all-copper wiring system can actually be faster than an optical system, even though the optical media has much greater bandwidth.

Automobiles are an application made to order for optical cable. In fact, cars may have to use optical wiring if the electronics continues to proliferate at its current pace. Eventually, a car will contain numerous internal control networks. Engine control is now fairly common, and it will be joined by a ride-control network that adjusts the suspension to road conditions, braking and traction controls systems, and a passenger convenience and comfort network that controls temperature, entertainment, and so on. Optical cable is much smaller and lighter than a conventional wiring harness and optical media is almost immune to the critical emi/rfi noise environment of the auto. Optical cable also may eventually fit in with the concept of multiplexed control where a microprocessor divides its time among various functions within a control group.

Optical cable and multiplexing will also play a role in future office equipment and “smart homes.” A smart home will be microprocessor controlled, essentially bus-wired, and contain electronics that make it possible for the owners to program a wide variety of functions.

Though copper cable is virtually universal in local-area networks, that may change in the next few years. Optical glass fiber will certainly be required for high-speed local networks, such as the upcoming fiber distributed data interface. However, plastic fiber with its relative ease of termination and continued performance improvements may appear more and more attractive during the decade as a cost effective means to interconnect small departments within large organizations.

Resistors can offer creative solutions to design problems

Application-specific resistors (ASRs) are one of the most significant of a wealth of developments resulting from improvements in resistor materials and processing techniques. Specific resistors can offer lower cost, higher performance, and smaller size than off-the-shelf resistors. ASRs will be applied to a wide variety of design problems, including size, cost and noise reduction and temperature coefficient compensation. The 1990s will see a continuation of the trend toward tighter tolerances, as well as continued size reduction, without corresponding power rating reduction in many cases. Surface-mounted resistors will be the dominant technology, but leaded resistors will continue to be used for special requirements.

Resistors are generally perceived as the most mundane of electronic components. The typical design engineer thinks of them as simple devices that have remained unchanged since he was in school. However, there are continuing significant developments in resistors and other resistive components that deliver cost-effective solutions to new and existing circuit demands.

Improvements in resistor materials and processing techniques have led to a host of developments. I think the most exciting development is the application-specific resistor (ASR). Range extensions at both ends of the resistance scale have expanded–gigaohms at one end and fractional ohms at the other–with each incremental extensions opening up new application areas.

Specific resistor types with higher performance, lower cost, and smaller size have replaced earlier styles or more costly resistor types. In the past, for example, a close-tolerance power resistor had to be wirewound. Now, for power ratings up to 10 W, film devices are every bit as stable. During the ’90s, that 10-W figure will undoubtedly go higher.

I expect to see the continuation of tighter tolerances. Tolerances of 5% and 2% will fade away as production processes improve. The 1% tolerance will become the leading figure for film resistors.

Size reductions will continue, often with no reduction in power rating. I expect the 1/8-W size to displace the 1/4W size as the volume leader during the next decade. Surface-mounted resistors will continue to get smaller and command an increasingly large share of the market. The continued downsizing will increase the use of passive networks. The parts are becoming so small that even the best automated equipment has great difficulty handling them individually. As a result, the passive network will become the form factor of choice in mounting these units onto circuit boards. Instead of users handling 15 or 20 things that resemble little specks of pepper, they’ll handle 2 or 3 networks that have those specks on them. The networks will also get smaller, but not small enough to present a problem.

Although surface-mounted resistors will dominate the industry, leaded resistors will continue to be in demand for special requirements, such as high power, fuseability, ultra-precision, and customized impedance.

The ASR will emerge as an extremely cost-effective solution to many knotty design problems. In the past, design engineers didn’t usually think of ordering custom resistor products and resistor makers didn’t push them very much. The reason was that we didn’t have much to offer. Thanks to various developments in ceramics, filming techniques and materials, and coating techniques and materials, we can now offer inexpensive ways out of numerous design difficulties.

One case that exemplifies this point concerns an engineer who built a prototype of a piece of high-frequency communications equipment with standard off-the-shelf resistor at a critical point in the circuit. When it came to volume production, similar resistors caused the circuit to malfunction. Although it apparently was identical, the production resistor had a slightly different capacitance, and hence as slightly different rf impedance. We could adjust the geometry of our standard product to give that designer the impedance his design needed.

Design engineers are constantly pressured to reduce the cost and size of their circuits. ASR components, where appropriate, are an effective means to achieve both objectives.

We’ve built resistors with a dab of nickel-bearing epoxy painted over the regular coating to form a resistor with a bypass capacitor connected to one lead. That’s an extremely cost-effective way to reduce noise in a sensitive high-gain amplifier. Another ASR was built with a particular temperature coefficient (TC) to compensate for a capacitor’s TC. The RC combination then maintained a very stable time constant over temperature. The solution was elegant and much cheaper than the brute-force approach of trying to get both TCs down to zero.

There’ll be more such innovation, whether it’s special resistor in a spark plug or a lamp ballast. Engineers must be aware of the possibility of solving problems with a custom resistor. Most of them won’t consider discussing problems with resistor application engineers. And that’s too bad, because these products won’t be found in any catalog.