The International Solid-State Circuits Conference (ISSCC) conference is in full swing. Chipworks is attending to track the newest ideas in circuits and chips for 2012 and are blogging a few notable highlights.

Hynix presented a paper entitled ‘A 1.2V 23nm 6F² DDR3 SDRAM with Local-Bitline Sense Amplifier, Hybrid LIO Sense Amplifier and Dummy-Less Array Architecture’.

While the author touted a number of circuit innovations, including a modified sense amplifier and LIO amplifier, the most interesting modification they discussed was the removal of the need for dummy cells in the memory array.

In current DDR3 SDRAMs using 6F² architecture the edge arrays are only half utilized as the sense amplifiers are located between arrays and require the bitline capacitance to be balanced.  This means that there are actually thirty-three arrays, two of which are only 50% in use. Therefore over 3% of the memory cells on the die are unusable. In fact, some DRAMs have an even higher fraction of cells that are unusable. For instance, in the Elpida 46nm 2Gb LP DDR2 SDRAM we are currently analyzing in our labs we see a full array as 25 sub-blocks (with 2 of these sub-blocks only ½ usable). As such, a full 4% of the cells on this DRAM serve no function.

Die Photo of Elpida B4064B2PF LP DDR2 SDRAM

Hynix have proposed using only thirty-two memory arrays, and modifying the sense amplifiers for the bitlines that terminate on the outside edge of the array.  In order to balance the bitline capacitance, there is an offset, which is dynamic and based on the data that is being sensed from the memory array. In the cut-throat world of commodity DRAM pricing this 3% cell usage gain (which would translate to about a 1.5% chip area reduction) should have a meaningful impact on product competitiveness.

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In a previous post we discussed the massive push of really innovative products into the LED lighting market that, in North America anyway, doesn’t really exist yet. But consumers aren’t early adopters in a low-thought purchase like light bulbs.  Good thing technical people are always looking for the bleeding edge you say. This is not always so in the power industry where things designers know, trust, and are on the periphery are often best left alone.

The very technical people that are building power supplies for the latest washing machines, handheld electronics, and server farms have a hard time letting go of what they know. Moreover, they often have a hard time justifying potentially higher costs and risks on a new feature that their end customer doesn’t value. It is hard to balance a 3% improvement in vampiric power draw against an increase of the BoM cost on that particular feature.

We saw this theme a few times at APEC 2012. There was the LED lighting discussed above, the reluctance of some designers to adopt digital controllers even when the application might be better suited to use them. But none more saliently than a fantastic demo in the ON Semiconductor booth.

Space Invaders running on a Commodore Vic 20

ON Semi was showing a part that they still sell in high volume called the TL431: Programmable Precision Reference / Shunt Regulator, This is a part that dates back to the Commodore Vic 20!  The sign above the display said, “Time for an Upgrade?”  What stronger challenge is that?  Editorial note – we at Chipworks are very partial to this kind of demonstration because the entrance hallway to our corporate head office includes a computing museum with a slightly more modern Commodore 64.

This particular dinosaur was actually a fully working demo. No emulator hidden under the counter here. ON Semi was selling the point that, although there is demand for the product, they have something new, the NCP431 that has modern features that should be considered when designing a power supply. With more and more power components 100% focused on lowering their parasitic draw while also improving peak efficiency to well over 90%, they are pointing out that some of the peripheral devices are now an important design consideration for the overall supply efficiency. So upgrade!

ON Semi demonstrated a few other products at the show, including the NCP1246 fixed-frequency current mode controller that, according to their press release, “achieves extremely low no load input power consumption in AC-DC adapters”.  The latest technology eliminates the need for resistors to bleed power for safety but detects the signal and switches off, reducing power demands. This impressive part works with the NCP4353 or NCP4254 secondary side switch mode power supply (SMPS) controllers to deliver input power of <10 milliwatt in a 65 watt notebook adapter. It also includes constant voltage and constant current regulation and optional built in LED driver for an adapter indicator light. Booth staff advised that it is sampling with customers and will be in full production at the beginning of Q2.

On the LED lighting side they were showing off the NCL30000 Power Factor Corrected TRIAC Dimmable LED Driver.  It isn’t brand new, but still the device performed well and dimming performance was impressive. ON Semi advises us that the device has over 90% efficiency and, like others, is doing primary side regulation to reduce the overall module part count.

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It is no surprise that High Voltage LED Drivers is one of the hottest topics at the APEC. In fact, a lot of people (in the average range of 300) flock to HV LED sessions in order to understand more about this technology while exhibitors, such as Fairchild, TI, Monolithic Power, NXP and many others try to showcase their HVLED portfolio. This industry is no cosy duopoly but a fiercely competitive one with dozens of billion dollar suppliers touting their latest products.

So with all these driver companies vying for sockets, why don’t I have a single LED light bulb in my home? Several speakers at the 2012 APEC conference either had a slide on the subject, or spoke to issues during their talk, so we will summarize here.

The power industry has a perception problem in the mainstream. Nobody understands it and LED is a clear example as to why:

1)      “They” use terms like 50,000 hour bulb life – which is confusing a consumer isn’t going to do that math at point of sale. Moreover, it is misleading since the buyer will think that their average bedroom light, that is used about 2 hours per day, will now last their entire lifetime (when the capacitors won’t)

2)      They tout fundamental changes in the national power consumption (lighting was shown during a plenary session at APEC to use 3% of the total grid so there are better places to put our environmental mindshare)

3)      They cite the low efficiency of traditional lighting but if a consumer is smart enough to know where the efficiency loss goes (heat), and if they live in a cool climate, then they are probably smart enough to know that waste heat is (a relatively expensive) benefit 75% of the year.

4)      They use terms like “color” to explain the light quality when compared to incandescent, they are all white. And a white that most of us aren’t really happy with anyway.

5)      And finally, since we can’t do the math, the bulbs have high cost compared to a $.25 incandescent one.

Despite these challenges, it still seems more than obvious that LED lighting is the future. Proof of the strange dichotomy in the power industry that innovates like crazy and making a real difference in small increments.

The history of LED lighting drivers started innocently and simply enough – according to Matt Reynolds of TI, people used to take a buck-boost converter and convert it to an LED driver. While that may work on Gen 1 LEDs, it is not going to work on Gen 2 and 3 LEDs.

He then talked about the retro-fit dilemma of having 250 billion sockets needed to fill, and if only (I/they) could get 1% of market share. In the rest of the technology industry there is no such thing as 1% market share (to quote the movie Antitrust, technology success is binary, you are either a one or a zero), but in power technology the market is crowded yet everyone seems to be successful, and gains are measured in small increments after all.

So what innovations are going on to make a good SSL LED IC Driver? Lower cost, high (improved)-efficiency, reliability, good LED current regulation, good dimmer decode, and  good system protection are among those mentioned.

One vendor solution for LED (Fairchild) - click to enlarge

LED drivers have been the weakest link in LED systems because of component failure, PCB board defect, lightning/surge failure, solder junction failure and so much more. Reynolds then talked about the possible solutions to these LED driver challenges such as the use of GaN, high-voltage LED stacks, and AC LEDs.

Having said all of this, it is no wonder why companies are showing off their chipsets and reference boards for LED lighting with new controller products from such as ON Semiconductor, NXP, Fairchild, TI, and Monolithic Power.

To finish up, here is a demo video on the dimming quality of today’s chips in the Monolithic Power booth.

After all, the mythical 1% market share in the case of LEDs, is a whole lot of sockets.

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Transphorm, which offers the industry’s first qualified 600V GaN device, states that GaN is the choice of power device at higher frequencies. That is, GaN’s frequency-loss ratio shows that it has twice the advantage over SiC and 14x advantage over Si. Yifeng Wu (V.P. Product Development) took the stage at APEC 2012 to explain.

Yifeng Wu, VP of Product Development at Transphorm

Comparing performance

According to Wu, VP of product development, GaN replaced SiC LEDs within 3 years of the first product, going from research to a fully qualified product in 5 years. GaN then entered the RF market and is rapidly growing from the first power amplifier in 1993 to production in 2003. The next market is power, where GaN has gone from the first devices in 2000 to now being in production.

GaN Commercialization

Wu then stated that the GaN high band-gap transistor not only sustains high electric field with a short drift region, its GaN buffer layers are suited for low leakage and high breakdown voltages, and is normally off, which is ideal for use in the power market.

Block Diagrams of Device

Transphorm proceeded with an implementation of a typical boost converter using their proprietary GaN power transistor. The presentation compared the performance of GaN with Infineon’s CoolMOS to show the benefits of their technology. This comparison spanned almost half of the talk but here are some highlights.

A graph showing the di/dt between the GaN transistor versus the CoolMos shows that when both devices were tested at 450A/microsecond, Transphorm’s GaN HEMT came out with little ringing while CoolMos was unstable.

Comparing coolMOS with GaN

During the question and answer portion, Wu stated that Transphorm’s 600V GaN power device has a better breakdown voltage compared to the Infineon CoolMOS. Its thermal characteristic is similar to the CoolMOS while its input capacitance is 1/5 of a CoolMOS.

But can the technology compete with the CoolMOS for all applications?  Not necessarily. Firstly, the expectation is that it will only be price competitive in the next “5 to 10 years” so the focus for GaN FETs by Transphorm is in the higher value markets. Additionally, Wu indicated that they have only qualified their solution to 150 degrees and that it should not be used for applications with a high spike design. However, to quote the answer to an audience question about yields, “yields are good and if you place an order for as much as you want, we’ll ship it.”

While we haven’t looked at a Transphorm device yet, we have looked at a CoolMOS, and if you place an order on this link, we’ll ship it!

Die Photo of Infineon IPB50R299CP CoolMOS Chip

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We took the chance to sit down with Michael Gilbert, Senior Product Marketing Manager for Isolated Power.  Long title, but he presented some of TI’s roadmap and coverage in the power sector and they seem to have the breadth and technology to continue their growth (dominance?).

They were right on top of the news makers in GaN by announcing several FET drivers that were specifically architected for GaN devices. This is a new market and Mr. Gilbert was, “not aware of anyone other than Transphorm and EPC that were producing in any kind of volume”. That said, TI has invested in what is a very promising technology.

Comparing the size of Si and GaN Devices

The designs specifically handle GaN challenges like, “never going above 6V at the gate and getting to zero very fast”.

Specifically they have the LM5113 100V integrated half bridge, high-side driver, the new LM5114 low-side driver, and the new UCC27511 high-speed 4-A/*-A low-side driver. You can see the influence of some National Semiconductor part numbers here. They are also launching a “coming soon” 5.4 MHz, 4.5-V to 60-V synchronous buck controller for GaN FETs or MOSFETs expected to be in the hands of clients towards the end of H1.  The point is, TI is investing heavily in the latest upstart technology.

TI Digital Power Ecosystem

In terms of the overall coverage, TI is acknowledged as having a huge analog portfolio, but from their ecosystem slide they certainly have coverage in the digital power ecosystem, whether this is with traditional analog chips, analog solutions with digital interfaces or mixed signal MCUs. And they continue to invest.

At the show they announced their next generation digital controller for isolated power, the UCD3138 and it is touted as the first highly integrated controller optimized for AC/DC and isolated DC/DC power supplies. Rather than re-purposing existing technology, the device was specifically designed for this application to limit die size and keep the cost very competitive. It includes 32K of flash, an ARM7 32-bit processor, high speed precision data converters, multiple programmable hardware control loops, analog peripherals and various communications engines.

UCD3138 Architecture

As a digital device, they have the expected GUI-configurable programmability and also includes advanced monitoring capabilities. Several development kits are available from TI.

• Development kits:
  • UCD3138PFCEVM-026: Universal input, 400-Vout AC/DC PFC development kit, configurable into single- or two-phase interleaved and bridgeless topologies
  • UCD3138PSFBEVM-027: 400-Vin/12-Vout DC/DC phase-shifted full bridge
  • UCD3138LLCEVM-028: 400-Vin/12-Vout DC/DC half-bridge resonant LLC
  • UCD3138HSFBEVM-029: 48-Vin/12-Vout DC/DC hard-switching full-bridge
• Reference designs:
  • Universal input, 12-Vout 600-W AC/DC reference design (PFC plus LLC, and PFC plus phase-shifted full-bridge)
  • 48-Vin/12-Vout 1/8 brick DC/DC reference design (hard-switching full bridge)

More to come from APEC – stay tuned!

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First, the difference…

A switched-mode power converter is a discrete control system that uses an analog controller. This analog controller is a PWM generator and a compensator (as shown below).

A digital power converter on the other hand, is still a discrete control system, but the analog controller has been replaced with either a digital controller or an MCU (as shown below).

So why do we need digital power?

• Reduced manufacturing cost
• It enables higher quality such as higher noise immunity
• Higher reliability

So what’s keeping people from using digital power as oppose to an analog controller?

Since digital power is new to a lot of people, not a lot of things about it have been explained in literature or textbooks.  We documented many of the myths of digital power previously, concluding in summary:

1. Digital power is not slower than an analog controller
2. Digital power’s quiescent current is similar to analog controllers
3. Digital power can run sophisticated algorithms which optimizes power and efficiency.
4. Digital power is as accurate as an analog controller since one would need greater than 10-bits of resolution to accurately regulate a 12V to 1.2V converter; 14-bit digital power designs are now in use.
5. Digital controllers do not generate more noise than analog controllers and many are being marketed based on generating less
6. Digital power designs are denser than that of analog controllers because digital has more functionality in them.
7. Digital controller chips are price competitive in the mid to high end, providing similar pricing and more features.
8. Digital power solutions are often less expensive and more reliable than analog controller solutions because of higher levels of integration and fewer chips in the overall BOM.

Switched-mode power converters, otherwise known as analog controllers, are here to stay; however, digital power controllers, which are now being used and studied, will someday takeover the power conversion industry.

At the APEC 2012 sessions, we noticed that dc-dc converters/power converter engineers were mostly interested on how the PWM controllers were designed. To them, knowing how the PWM controllers work is of the utmost importance. So there may be an opportunity to change some of the way products are marketed.  Instead of marketing dc-dc converters as having high efficiency (e.g. 92%, which is by the way very common), or by marketing them using the process used in the power switch, why not say the PWM controller uses “true current algorithm, etc., etc.”.

Digital power controllers are slowly being introduced as replacements for analog controllers. Though we all know that digital power controllers are still in their infancy stage, they are now coming out in the power conversion world and we should be on the lookout especially in possible applications such as high-voltage LED drivers.

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APEC Day 1 – a review of the APEC 2012 conference plenary sessions:

The plenary session for APEC 2012 featured keynote-style presentations from several industry leaders covering the future of power technology. Nobody was joined by any members of the Black Eyed Peas. Power is the meat and potatoes of the technical world.  However there was no lack of vision.

The main theme was aptly put by Tektronix President, Thomas Buzak  when he said, “we want to help you change the world”.  An industry that is based on driving motors and making our computers turn on and work is going to change the world.  Wow.

But this time, it isn’t all hyperbole. It is no secret that everything in the electronics and semiconductor worlds get smaller, better, and faster. However, with the global focus on power, the amount of R&D funding, and the pace of innovation today some of the results of the “power technology industry’s” work is truly inspiring. Rather than tell you things are getting smaller(er), better(er), faster(er), we thought we would take a few pictures from the slides to show you.

Almost every presenter used some, or all, of three examples to show the impact of the power technology industry on our very planet.  Specifically, (a) new ways to generate power, (b) LED lighting, and (c) electric vehicles. As the most visible applications of power technology, it makes sense.

On the electric vehicle front, the oft criticized Chevrolet Volt was shown, as an illustrative example in a presentation by Dr. Babak Fahimi, Professor of Electrical Engineering, University of Texas. What we liked about it was the simple equation to explain it. Now that you know the math, you now know all you need to know about electric cars.  Now go out and buy one!

Reducing the Chevy Volt to an Equation?

Seriously though, current motor types don’t have the necessary cost/power density to be effective in meeting consumer expectations of what an automobile should be.  Dr. Fahimi suggested that the “best” drive technology (Interior Permanent Magnet or IPM) is still far too costly and price-volatile, citing that the price of Neodymium had increased from $50 to $460/kg in 2011 (and has since fallen back somewhat to ~$220).

So if electric cars are still a few years away from meeting the price-value point then surely we will be talking about Hybrids like the Toyota Prius. No, No. This is a meat and potatoes show that thinks BIG.

Phoenix International’s John Oenic, Director of Power Electronics was showing the “The Challenge of Developing Electric Traction Drives for Heavy Duty Work Vehicles”.

Looking at the history of electric drives, it is longer than the average consumer would think. In the 30’s DC drives were applied to locomotives and then applied to large trucks in mining locomotives in the 60’s, and anyone (at least of a certain age) from the U.K. remembers the electric milk trucks from the days when they actually delivered milk to your door.  In those cases it is because it was the only working choice for high power low speed.  The economic model fit. He posits that the economic argument is moving hybrids to construction equipment and long haul vehicles because in high-hour vehicles the basic math is in their favor.

In 2011 John Deere introduced 2 hybrid loaders. According to Mr. Oenic, they are more productive while using less fuel and putting out fewer emissions. All power is transferred via electric conversion to mechanical torque. The company didn’t need to go exotic for thermal performance but needed high reliability.  For instance, some loaders supplying coal to a power plant will run for 8500/8600 hours per year. He considered two key issues to be (unsurprisingly) heat and reliability.

The other automotive challenge is that they also need to design for safety standards that are extremely high.  For electric vehicles, EU Homologation requires demonstration safety/reliability of 10X the amount of a normal automobile.  If it has 1 electric motor per wheel then it must be 10,000x more safe.  According to Mr. Oenic, this is up at the level of aircraft.

The next to take the stage was Dan Kinzer, CTO and Senior VP Fairchild Semiconductor talking very macro-economic on “Maximizing fossil fuel savings through power electronics.”

Dan Kinzer, CTO and Senior VP Fairchild Semiconductor

There was a lot of emissions data, and discussion of industry growth drivers like new technology. A good example is the SiC bipolar junction transistor. It has wide bandgap, high breakdown field, high temperature stability and can achieve 800V with a switching speed of 20 ns and very small loss in the transistor. Other drivers included:

- growth in electric and hybrid vehicles (discussed earlier)

- LED lighting where market-share is currently so low that it is effectively zero. He felt the cost needed to fall at least 10 times before consumers will want to consider the move.

- Regulations around the world. For example in 2010 China and India put in place motor efficiency standards.

- Solar where the cost of electronics is going to need to drop by at least 50% in order to achieve $1/W

- Drive to improve generation and distribution

On the last bullet, since much of the worlds electricity is generated with fossil fuels, transmission is a major area for improvement . Transformers loss accounts for 37% of the overall transmission lost (61% is line loss). Efficient transformers could save the globe tons of CO2 emissions. A smart grid is another great way to go as it cuts losses.

What about the trends in the devices themselves? A nice chart summed-up the direction.

Segmentation of Power Devices

And the final speaker took things up a notch again.  Dr. Vlatko Vlatkovic, GM of Engineering and Technology, GE Coverteam talked about, “Power Electronics for Energy and High Power”.

Dr. Vlatkovic said, “For me 1 megawatt is low power and I am interested in hundreds of megawatts”.  Remember in faster, better, cheaper, “better” means more.

The first 50 years of electrical power generation was about massive gas turbines – all mechanical.  It is also a great service business because they use high temperature components that need to be repaired.

Comparing mechanical and electrical efficiency

Today, over 60% of compressors in the oil and gas industry use electric drives. Why? A good gas turbine only has about 26% electrical efficiency but an electrical drive has 40% efficiency. Again, unlike in the consumer space, the economics works. Additionally, electrical equipment requires very little maintenance , “you can leave it alone for 20 years”.

GE has a project, funded by the US Navy, to develop megawatt SiC systems. Using Cree silicon they built SiC transformers that were over 10x smaller. The example shown was straight forward silicon packaging technology and he feels that a press pack IGBT package is not a big leap.  But innovation in packaging is required for these long life high power systems.

Smaller transformers enabled by power technology

Applications for “smaller” are very compelling. For example, this technology lets oil extraction to move from huge fixed oil platforms to small mobile platforms that enable deep sea exploration and extraction. So innovation in alternative power generation, transmission and use will help the world last a little longer on it’s more difficult to extract fossil fuels.

“It is all enabled by power electronics.”

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Contributed by Rob Williamson.

Digital Power Controller – “it is all about design”

At APEC 2012, Intersil’s Chris Young, Senior Manager of Digital Power Technology, presented “Digital Power Mythology”. It walked us through a number of myths related to digital power management and control (henceforth called “digital power”) and explained how those system engineers who have traditionally steered clear of digital power should trust it to be at least as effective as analog power.

Chris Young, Senior Manager of Digital Power, Intersil

In presenting the argument that digital power should be the preferred solution he cited some examples, “many UPS solutions today use digital power and that it is an option on the PM (12 and 12.5) bus for Intel processors. By 2015 it is my opinion that all of Intel’s processors will be specifying digital power.”

With regards to performance, “many experiments have been done with the same board set-up but swapping out digital and analog control and they are often shown to be highly similar”. In the examples presented digital had a slight performance benefit.  He was clear to point out that although a slight improvement may only save 1 watt, when you multiple the benefits across multiple power supplies on board, and then multiply that in an environment like a server farm then you have the potential to save the customer a lot of money. For systems designers, where a lot more of the potential can be realized is that they do not need as many components on a board and therefore the overall systems efficiency is better.

The presentation aimed to dispel the myths associated to digital power, and present them as no longer true. Subdivided into three categories- performance, economic, and usage. We’ll focus on the top two because their descriptions were a bit more technical.

Performance Myths

1)      Is digital power slower than analog power because the additional A-D / D-A conversion?   Author, says “NO, since one can just use an intelligent circuit design and make the whole thing as fast as you want”

2)      Does digital power need a high clock frequency for high speed response?  Author, says, “No”

3)      Does digital power require higher quiescent current than analog control? Author, says, “No, again, some digital controllers have lower quiescent currents than analog controllers”

4)      Is digital power is more efficient than analog? Confirmed as digital power uses the central clock system

5)      Is Digital power is not as accurate as analog ? Author, says NOT, since most digital controllers uses 14-bit DPWM controllers. In fact, digital controllers can be much better calibrated than analog”

6)      Does digital power generate more noise than analog? Author, says , first analog controllers are not immune to noise, and in fact, there are several digital controllers are now being marketed on that basis of low noise compared to other digital controllers.

This was a 3 hour session, so we’re going to focus on a few “myth dispelling” highlights. For the full presentation, you may want to find Mr. Young on LinkedIn – he was a good speaker and certainly passionate about digital power.

Analog vs Digital Power

Looking at the typical analog controller, you have a simple well understood design with a short path.  However, there is not a lot of bandwidth available so it is not infinitely fast. A digital power controller uses a clocked system with an ADC (with some latency) a digital filter (with some kind of group delay) then you have the PWM with latency.  However, it is worth noting that analog can have latency and bandwidth as well.  A typical analog power supply control loop has loop bandwidth  <200 kHz and digital power is more than up to the task.

In digital power, with 1 MHz sampling, 1 sample delay then at fsw/5 has 75 degrees of phase lag. So quite a significant lag?  But is this lag an issue?  Not if intelligent design is used.  Most likely method for design is to do over sampling. “Demonstrated a close loop regulation of >12 MHz fsw. Using a 0.18 um CMOS digital logic cell is between 20 and 50 ps.”

And it is not a simple matter of turning up the clock.  Putting a clock of 1+ GHz in a $1 or $2 pwm chip doesn’t make economic sense, but you don’t need > 1GHz clocks. By using a tapped PLL you can make a full oscillator to increase resolution. You can also dither the lowest significant bit of the PWM pulse over 8 to 32 cycles providing another 3-5 bits of resolution. The result is a 9 or 10x reduction in clock frequency required. Additionally, you can reduce the clock speed when the frequency is at steady state. The bottom line, states Chris, “For power management, you can do digital circuitry as fast as you want and as fast as you need.”

Myth #734 (there were quite a few and we lost track)

With respect to resolution, increasing resolution to greater than 10 bits (there are already plenty of 14 bit controllers on the market) results in more than sufficient resolution over the voltage ranges. In addition, digital controllers can be much better calibrated than analog and can consider a very wide range of temperature variability and  thermal compensation. And most particularly, there is no drift. You never have to worry about “0 drifting to .01 in the digital world.”

With proper design, issues around resolution, limit cycling, duty cycle dithering, noise, and compensation are not relevant and digital can be equivalent or better.  With digital solutions you can build smaller power supplies and have significantly more features.

The basic and oft repeated statement was -  It is all about design.

Economic Myths – Digital controllers are more expensive than analog controllers

It is true that you can get some analog controllers for under $.10, but you can also get full featured analog controllers that cost $5.  At the lowest end, digital controllers are more costly, but digital controllers have a wide range of pricing.  Additionally, isn’t an apples-to-apples comparison, because digital controllers are typically full featured with capabilities for data analysis, autoconfiguration / calibration, monitoring, etc.  Chris said “comparing a digital controller to an analog controller is like comparing a car to a bicycle.”

Comparing cost and value for digital vs analog

When considering the full system, digital power offers features for margining, power management, fault management, etc. and reduces the total BoM of devices, inventory costs, failure rates, manufacturing costs etc. since many digital boards can have less than ½ the total number of devices.

From a chip design point of view, the more you can put on the MCU the more you can scale the solution from process generation to generation. And that makes good sense since we are talking about a huge number of sockets.

Design density of analog and digital power

From a usage standpoint, digital power was presented as easier to use, as having less inherent risk (compared to analog), and being quicker to design. On the risk side, the main reason was that the overall BoM could be lowered with fewer components to buy, inventory, manufacture, and test. From the ease of use and design perspective, a good deal of time was dedicated to demonstrating Intersil’s simple GUI interface that designers could use to monitor and tweak the power supply.

In summary (if you haven’t heard it enough by now), it is all about design.

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The coupling of an electrical signal, while providing high voltage galvanic isolation between two parts of a circuit, has always been a technical challenge. The main solution, since at least the early 1960s, has been to use optical coupling. The electrical signal is converted to light using a light emitting diode (LED) or even a small incandescent lamp. The light crosses the gap that provides the electrical isolation, and then the signal is converted back to the electrical domain with a photodiode or a photoresistor. Typically, opto-isolators are unidirectional devices; however, it is possible to build a bidirectional device by using a pair of LEDs placed face-to-face.

An example of a unidirectional opto-isolator is the Renesas PS9402, which was recently analyzed by Chipworks. The PS9402 is an optically coupled isolator containing a GaAlAs LED on the isolated input side, and a photodiode, signal processing circuit, and power output transistor on one chip on the output side. It also includes an isolated fault output. The PS9402 provides 5000 V breakdown isolation between the input and output pins.

Figure 1 shows a cross section through the PS9402. A signal from the input pins is converted to the optical domain by LED1. The light propagates across a gel filled cavity and is absorbed by the photodiode integrated into the BCDMOS die. The high voltage isolation gap is between the upper and lower lead frames. The LED2 is used to couple the fault signal back across the high voltage gap.

Figure 1. Renesas PS9402 Package Cross-Section

Optical isolators are a well established technology; however, due to the nature of the devices, they tend to have high package integration costs, hence a number of vendors have recently developed so-called “digital isolators” which keep the signal entirely within the electrical domain. A variety of different methods are used by the various suppliers of this new technology. The suppliers include Analog Devices, Infineon, NVE Corporation, Silicon Labs, and Texas Instruments. Chipworks has completed a suite of reports on these technologies. Some highlights of these analyses will be summarized here.

Analog Devices iCoupler digital isolators use monolithic planar isolation transformer structures to couple a signal across the high voltage isolation. The Infineon devices are based on a similar transformer technology. Figure 2 shows an X-ray photograph of the Analog Devices ADUM1200 digital isolator. The package contains two die. The transmitter die features three transformer coils, seen in the X-ray, that couple the signal across a layer of polyimide dielectric material.

Figure 2. Analog Devices ADUM1200 Package X-Ray

A cross-sectional view of one of the transformer coil windings in the ADUM1200 is shown in Figure 3. The cross section shows the top and bottom transformer windings separated by the polyimide insulating layer. According to the device datasheet, this polyimide can support up to 2500 V RMS.

Figure 3. Analog Devices ADUM1200 Isolation Transformer Windings

Texas Instruments and Silicon Labs use capacitive coupling to bridge the high voltage gap, rather than inductive coupling. The Texas Instruments ISO7220A is a dual-channel digital isolator. This device has a logic input and output buffer separated by TI’s silicon dioxide (SiO₂) isolation barrier, providing galvanic isolation of up to 4000 V. Figure 5 shows a cross-sectional SEM picture of the edge of the pads. The bottom capacitor plate is formed with an N⁺ substrate diffusion, with the top and bottom plates being separated by the full dielectric stack on the die. The Silicon Labs technology, shown in Figure 6, is quite similar, except that the top plate was formed with metal 6 and the bottom plate with metal 1, in a six metal CMOS process.

Figure 4. Texas Instruments ISO7220A Isolation Capacitor Edge

Figure 5. Silicon Labs Si8422BD Isolation Capacitor Edge

NVE Corporation digital isolators are based on a novel technology called GMR, or giant magnetoresistance. The GMR effect is observed as a significant change in the electrical resistance, depending on whether the magnetization of an adjacent ferromagnetic layer is in a parallel or an anti-parallel alignment. The overall resistance is relatively low for parallel alignment and relatively high for anti-parallel alignment. Figure 7 is a schematic diagram illustrating the operation of the NVE digital isolators. The magnetic field from a winding coil induces a change in the resistance of the GMR layer, which is sensed using a Wheatstone bridge structure. The benzocyclobutene (BCB) provides the high voltage electrical isolation. The GMR film is comprised of a thin, less than 100 nm, stack of permalloy (FeNi), copper, and antiferromagnetic CrPtMn. These films are deposited in the presence of a magnetic field, as described in the NVE US patent 7,557,562 B2, 2009.

Figure 6. Illustration of GMR Isolator

The NVE IL715-3E is a four channel unidirectional high-speed digital isolator. It is a CMOS device manufactured with NVE’s patented IsoLoop® spintronic GMR technology. The device apparently will provide 2500 V RMS isolation. Figure 8 shows the planar magnetic winding coils found on the top surface of the IL715-3E. The magnetic field from this coil results in a change in the GMR film resistance in the underlying Wheatstone bridge, shown in Figure 9.

Figure 7. NVE IL715-3E GMR Isolator Winding Coil and Bond Pads

Figure 8. NVE IL715-3E GMR Sensor Wheatstone Bridge

This brief survey illustrates the broad variety of technologies that have been used to bridge a low voltage signal across a high voltage gap. As discussed, optical coupling has historically been the method of choice; however, this is now being replaced by electronic methods based on inductive capacitive or magnetic coupling.

Chipworks Report References

• Analog Devices ADUM1200WTRZ Digital Isolator Process Review
• Analog Devices ADUM2200SRWZ Digital Isolator Process Review
• Analog Devices AduM1100AR-RL7 Digital Isolator Digital Isolator Receiver Partial Circuit Analysis
• Infineon EICEDRIVER® 1ED020I12FA IGBT Driver with Paired ICs and Planar Coreless Transformers 0.8 μm CMOS Process Process Review
• NVE IL715-3E GMR Type Digital Isolator (30457 J Die Markings) 0.50 μm CMOS Process Process Analysis
• Renesas PS9402 IGBT Driver with Photocouplers and 0.5 μm BCDMOS Signal Processor Process Review
• Silicon Laboratories Si8422BD Low-Power, Dual-Channel Digital Isolator TEM Analysis of Isolator
• Silicon Laboratories Si8422BD Low Power Dual Digital Isolator Circuit Analysis
• Texas Instruments ISO7220A Capacitor Type Digital Isolator Process Review
• Texas Instruments ISO1050DUB Isolated CAN Transceiver Circuit Analysis of Logic I/O Buffer

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A Plethora of OLED TVs at Samsung's CES Booth

The thing that I didn’t expect was how thin OLED screens are – here’s an edge-on shot:

Edge-on Shot of Samsung OLED TV

I would guess 15 mm thick, though there’s probably a published spec somewhere. I gather the Best of Show LG 55″ OLED TV set is ~4 mm thin – amazing! Can’t wait to get one!

Not satisfied with walls-full of screens, they also had the Samsung SUR40 multi-touch-screen table display:

This again is better seen in motion:

The picture below shows information instantly downloaded from the RFID card lying on the surface.

Elsewhere in the booth was another surprise – who would expect the return of vacuum tubes (valves, for us Brits):

An Intriguing Entry - Vacuum Tubes?

When we went in there, no vacuum tubes on display, presumably they were all inside the boxes on show. Hi-fi buffs have long alleged that analog valve amplifiers give better sound, but this is the first time in years that I’ve seen a new one! Samsung uses the vacuum tube in the pre-amp.

Schematic of Samsung Audio Amplifier

Another example of technology repeating itself – hardly the “new era of sound”!

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