Digital Isolators: New solutions to an old problem

January 27th, 2012 by chipworks

Contributed by: St.J. Dixon-Warren, Rajesh Krishnamurthy, Tim White, and James Mihaychuk

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

Miscellanea from CES – Samsung OLED TVs, Touch-Screen Table-Tops, and Vacuum Tubes..

January 18th, 2012 by Dick James

While at CES we didn’t get much time on the show floor, but we did get a quick walk through the Samsung booth which was absolutely dominated by OLED TVs, with at least a hundred OLED screens on show. You can get a sense from the photo below, but to do it real justice, check out the video. The colour quality was impressive, and Samsung had some great stuff cycling through the TVs.

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.

SUR40 Touch-Screen Tabletop with RFID Read Capability Through 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”!

Texas Instruments, “SimpleLink”…Cooking Meatballs from Anywhere

January 18th, 2012 by jmorrison

Last week at CES we had a great time visiting the Texas Instruments Wireless Group. We met up with Heather Ailara. Heather is the Media Relations Manager for TI’s Worldwide Wireless Communications Wireless  Business Unit. Heather introduced us to Matt Kurtz, the worldwide platforms and channel marketing manager for TI’s wireless connectivity solutions business unit. 

Matt introduced us to a new definition of a term that I have been using for sometime now; “connected devices”. Matt’s definition was very different than mine. When I speak of connected devices, I think of tablets and smart phones and things like this. When Matt speaks of connected devices, he is speaking of crocks pots. Yes I said it, crock pots. 

Texas Instruments CC3000 SimpleLink
The world of connected devices

 

Texas Instruments introduced us to a platform of low cost, low power products that are going to re-shape our future. One of the products is the SimpleLink Wi-Fi CC3000 chipset supporting the IEEE802.11 b/g standard for WiFi connectivity.  This chipset is uniquely designed for the special purpose of running in conjunction with low cost, low power Texas Instruments microcontrollers. 

The demonstration that really caught my attention was the operation of a Hamilton Beach crock pot from a smart phone. With phone in hand Matt was able to turn the crock pot on or off and or adjust cook settings. Come on, I am on the ski slopes enjoying my day when I realize I want the meatballs to be ready in time for some apres ski spaghetti and meatballs. Whip out my iPhone and boom, meatballs on! I realize this may seem funny, but think of what the future holds. In time, virtually every device in our home will have the ability to be controlled remotely through our tablets or smart phones or whatever means you use to connect to the internet. 

Matt called it ubiquitous connectivity. Texas Instruments is offering a complete solution that is easy to integrate, low power, low memory foot print and not so MIPS-intensive. We speak of application processors in our smart phones running at 1.x GHz. To implement this solution, we need only speak of 25 MHz and a 16 bit MCU. 

When we had a chance to sit down and ask some questions, I jumped to the conclusion that these devices we being fabbed on older lines at TI on process nodes like 0.18 um or 0.25 um. But Matt surprised me. These devices are being fabbed on 65 nm low power CMOS at their foundries like UMC and TSMC and others. 

This was a surprise, but when you think about it, using a node like 65 nm, you get lower power, more die per wafer, smaller foot print and lower cost. And with a smaller node like this, you can hard code the WiFi software stack into ROM, taking the load off the MCU, and removing the need for high-end processors. Perfect for an application that could run into the hundreds of millions or even billions. 

This is an area of growth for Texas Instruments. This device is only the start of a roadmap – they see it as an investment in the future and hope that it will be a big percentage of their revenue in the years to come. I can see TI’s revenue portfolio looking very different in 2015 and beyond! I can see Texas Instruments doing just this. Who else can offer so much to deliver these emerging connectivity solutions? TI has the biggest portfolio of wireless technology, proven hardware, leading edge MCU’s, and world-wide support. 

Texas Instruments Portfolio for Emerging Connectivity Solutions

TI's portfolio for emerging connectivity solutions

This will take time to trickle into our home. I for one am looking forward to a future where I can control my home, truly, from my smart phone. I think I may look into getting an evaluation kit so I can retrofit my crock pot now, so I can get those meatballs cooking.

GLOBALFOUNDRIES’ Ajit Manocha Visits Vegas for CES

January 17th, 2012 by Dick James

For the last three years GLOBALFOUNDRIES has hosted a reception  at CES. Although they don’t exhibit there, or even take a suite for the show, they find it a useful way to connect with customers and the analyst and journalist community.  Held on CES Tuesday (Jan 10), I expected a large Intel-style gathering with lots of flash, but it was actually quite low-key in a hospitality suite at the Mandalay Bay Resort, with no more than thirty people there at any one time.

After the initial introductions, Ajit Manocha, CEO of GLOBALFOUNDRIES, stood up and gave a short speech celebrating the first silicon coming out of Fab 8 in Malta, New York. As announced that morning – the first wafers squeaked into 2011 as promised, coming out of the line on 27th December; and we can expect the first 20-nm silicon in June.  He also spoke of the recent management changes and plans for $3 Bn capex for 2012 revealed in an interview the same day, bringing the total capex for the last three years to almost $12 Bn, showing their commitment to stay the course in the industry.  He emphasised that “GLOBALFOUNDRIES  is not just Dresden”, and that the former Chartered Semi fabs in Singapore were contributing significantly to GloFo’s bottom line.

Ajit Manocha at GLOBALFOUNDRIES' CES reception

The roster of customers that were present supported that, since most were fabless companies with product using larger node processes than the 45- and 28-nm product from Dresden.  Notably, AMD was not present, at least when I was there. A good crew of GF management was there, including Kevin Kimball (VP, Global Communications), Mojy Chian (Senior VP, Design Enablement), and his colleague Derek Meyer, and Subramani (Subi) Kingeri, (VP of Design Solutions – 14nm), amongst others. There were a couple of wafers on show, unfortunately not from Fab 8 – that would have been really topical!

28-nm and 32-nm AMD Llano Wafers from GLOBALFOUNDRIES Fab 1 in Dresden

GloFo is clearly staffing up at Fab 8 – they held a job fair there last week and reportedly have hired 1,100 so far, heading for 1,400 by year end. By the look of some of their stock photos, they are still not 100% functional yet, but it obviously won’t be long!

GloFo shot of Fab 8 clean room - note the hard hats and hand-carried FOUPs!

Aerial shot of GLOBALFOUNDRIES' Fab 8 in Malta, New York Source: GLOBALFOUNDRIES

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Texas Instruments Medical; ECG’s, EEG’s and Pulse Oximeters

January 12th, 2012 by jmorrison

Think CES 2012 is all about tablets, smart phones and internet-connected fridges? Think again. We had the chance to talk in detail with the folks over at Texas Instruments regarding their medical device technology.

When you think of Texas Instruments do you think of Electrocardiography, Electroencephalography or Pulse Oximeters? I surely did not. But today after spending time with Texas Instruments’ Sonya Terry Medical Communications Manager, Robert Burnham Strategic Marketing Manager — Health & Fitness and Karthik Soundar, Business Development Manager – Health & Fitness, I just may.

Three years ago Texas Instruments made a strategic decision to get into medical devices for health, fitness and clinical applications. The 7 billion people on the planet (and growing) at one time or another are either going to need care or be able to take care of themselves better – that is one huge market.

Texas Instruments has  applied their design and manufacturing expertise to develop ultra low power SoC’s for applications like portable ECG’s, EEGs and pulse oximeters. These solutions can be pulled together to provide medical instrumentation companies a lower integration cost, and an overall solution that is more cost effective and smaller by as much as an order of magnitude.

They showed an ECG demonstration kit that involved three probes attached to a mannequin, leading back to a small central hub not much bigger than a thumb drive, and then going down to the wrist of the mannequin where a full color 2″ (approx.) display, showed all of the hearts activity. A more conventional solution, as we have all seen in hospitals, is considerably larger.

Texas Instruments ADS1298 ECG Demonstration

The “heart” of  this solution is the ADS129X, a family of ultra low power, 8 mm x 8 mm  (64 mm2) single chip solutions. Previous solutions were on the order of 1,850 mm2.  The ADS1294/6/8/4R/6R/8R are multichannel, simultaneous sampling, 24-bit, delta-sigma (ΔΣ) analog-to-digital converters (ADCs) with built-in programmable gain amplifiers (PGAs), internal reference, and an onboard oscillator. The ADS1294/6/8/4R/6R/8R incorporate all of the features that are commonly required in medical electrocardiogram (ECG) and electroencephalogram (EEG) applications. These devices are fabricated using a 0.35 um CMOS process.

TI advises us, that with all of this functionality integrated into a single chip they have enabled integrators to drop the end cost of an ECG solution from $15,000 to $2,500. This is a huge reduction in price that now puts this diagnostic capability within the reach of many more people.  This is a disruptive technology solution and will no doubt raise some eye brows at the big med tech firms like GE Healthcare, Philips Healthcare and Draeger.

Texas Instruments ADS129X Analog Front End Monolithic SoC

Texas Instruments ADS129X Analog Front End Monolithic SoC

Another product introduced to me today was the Texas Instruments AFE4110, a low cost MCU with integrated LCD driver. The AFe4110 is based upon TI’s MSP430 core and offers ultra-low power, small size and low cost by operating on a single 1.5 V battery. The AFE4110 features 16 kB ROM, 512B RAM, a 4×12 LCD driver with charge pump, a high accuracy oscillator, and additional features  that are perfect for digital thermometers, pedometers, thermostats and portable single alkaline battery devices. These MCU’s are fabbed on a 180 nm standard CMOS process and come in a bare die 2.7 mm x 1.1 mm.

Texas Instruments AFE4110 Low Cost MCU

Texas Instruments AFE4110 Low Cost MCU

Texas Instruments took a conscious decision to get into the medical devices business in pursuit of lucrative new markets. With an aging population, and the market for those who are trying to take better care of themselves, this looks like a wise decision, but can they be a winner?

TI is well poised to be a significant player in this industry because they bring significant depth and breadth in design and manufacturing as well as a global reach with field application engineers. Our guess is that this could be a tremendous market for TI in the future.

I think when we get back to the lab, we will decapsulate some of these devices and have a closer look at the die layout and utilization in order to post a follow up blog to share some of these die images with our readers.

Good Luck Folks.