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Dr. Holger Schmidt Nanoscale Optofluidics
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TA B L E O F C O N T E N T S TABLE OF CONTENTS
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Dr. Holger Schmidt DIRECTOR, W.M. KECK CENTER FOR NANOSCALE OPTOFLUIDICS
Interview with Dr. Holger Schmidt - Professor of Electrical Engineering, UC Santa Cruz.
7
Single Molecules on a Chip BY HOLGER SCHMIDT Exploring chip-scale integration of nanotechnology and integrated optics for biomolecular science.
Featured Products
10
Tradeoffs in New Generation ADCs
12
BY ED KOHLER AND JASON MESSIER WITH INTERSIL
Analog-to-Digital Converters are becoming increasingly pervasive, and Kohler and Messier offer critical tradeoffs for product design success.
Hey You, Get Into My Cloud
19
BY ROB IRWIN WITH ALTIUM
How web-based services will change the future of the electronic design process.
RTZ - Return to Zero Comic
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INTERVIEW
W.M. Keck Center for Nanoscale Optofluidics How did you get into engineering and when did you start? My original degree is in physics. My M.S. thesis project dealt with semiconductor devices with direct applications in fiber-optic communications. After my PhD work in Electrical Engineering on a similar topic, I decided to develop new optical devices and methods with real-world applications. What are your favorite hardware tools that you use? I enjoy working with a variety of lasers, in particular ultrafast lasers that produce short optical pulses only about 100 femtoseconds long. With these lasers, we can study materials on time scales that cannot be reached electronically. We also have recently set up a dual beam electron/ion beam microscope in our W.M. Keck Center for Nanoscale Optofluidics. An optofluidic device combines integrated optics with microfluidics. This can be a fluidically tuneable optical device, for example a fluidic dye laser, in which the active laser dye solution is contained in a microchannel on a chip. It can also be a device that uses integrated optical elements (waveguides, filters, splitters) to investigate or manipulate particles in a microfluidic channel, for example an integrated biosensor.
Dr. Holger Schmidt - Professor of Electrical Engineering; UC Santa Cruz
This is an extremely versatile nanofabrication and nanocharacterization tool that is a lot of fun to work with and allows us to both sculpt and image objects on the nanoscale. What are your favorite software tools that you use? I mostly work with MATLAB, do some programming in C, and design optical waveguide structures using simulation packages from Photon Design. What is on your bookshelf? I have recently read The Master Switch: The Rise and Fall of Information Empires by Tim Wu
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which deals with the fascinating story of the people and companies that invented new communication technologies and how they deal with issues of information control. The Elegant Universe by Brian Greene also tells a great story on the cosmic scale, presenting an introduction to string theory and its implications. I also read contemporary and classic fiction, plus a lot of children’s books with my family. Most recently, I read Aaron Hawkins’ The Year Money Grew on Trees which tells a great coming-of-age story that shows how hard work, persistence, and a great group of friends can accomplish almost anything.
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FEATURED INTERVIEW
Dr. Holger Schmidt
INTERVIEW
We need to stay one step ahead by providing cuttingedge training to our bright and motivated students. What has been your favorite project? For a number of years, I have had the vision of realizing optical quantum interference effects on a chip. Quantum coherence produces strange effects such as making opaque materials transparent, slowing light down, or making single photons “talk to each other.” Possible applications for quantum coherence devices include alloptical nonlinear devices (e.g., switches) that work on the few to single photon level, optical storage and memory, extremely sensitive metrology devices (magnetometers, interferometer), or single photon light sources and detectors. In collaboration with our colleagues at BYU, we have recently succeeded in slowing light down over a 1,000 times on a tiny silicon chip. Viewed
differently, we have taken a 20 foot long optical pulse and compressed it to a fraction of an inch on a chip. Do you have any note-worthy engineering experiences? Being exposed to a one million volt spark from a Tesla coil (http:// photon.soe.ucsc.edu/classes.htm ) while standing in a metal suit that acted as a Faraday cage and NOT getting shocked was one of the most exhilarating experiences of my teaching career. What are you currently working on? We’re using laser optics in a number of ways. We are studying nanomagnets for next-generation data storage media, will attempt to stop light on a chip to create optical memory devices, and are developing optofluidic chips for biomolecular diagnostics such as virus detection at the point of care. We use different methods to make the magnets. We make our own magnets using electron beam lithography. A photoresist is patterned with nanoscale holes; magnetic material (e.g., nickel) is deposited, followed by a liftoff process. We also get samples from Western Digital, San Jose, formerly Hitachi Global Storage Technologies. These are metallic multilayers deposited on nanosize islands that were etched into a substrate wafer. Finally, we work with a group at the University of Chemnitz, Germany, which deposits magnetic layers on top of selfassembled silica nanospheres. The spheres produce ordered patterns as they are spread on a wafer which
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can make for a very quick and inexpensive patterning step. The main application we are interested in at the moment is bit-patterned magnetic storage media for nextgeneration hard drives. However, nanomagnets are also relevant for memory devices (MRAM) or other emerging spintronic applications. What direction do you see your business heading in the next few years? I see a lot of potential in optofluidic technology—the combination of microfluidics and integrated optics. It allows us to look at devices that have been used for optoelectronic and communication applications in a new light. Their combination with non-solid media such as gases and liquids poses new research questions, but also has a lot of applications in the life sciences, biomedicine, toxicology, pollution monitoring, and other fields. What challenges do you foresee in our industry? We need to stay one step ahead, which will provide cutting-edge training to our bright and motivated students. ■
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Do you have any tricks up your sleeve? In my view, the keys to achieving breakthroughs in the lab are a combination of good planning ahead of time, persistence, the ability to recognize problems or new directions, and a bit of luck at the right time.
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PROJECT
The history of integrated photonics dates back to the late 1960s when researchers at Bell Labs proposed the use of thin film technology to create planar optical structures that would mimic the successful integration paradigm of integrated electronic circuits. The field grew rapidly along with the burgeoning area of fiberoptic communications. Even though early approaches to long-haul fiber links considered liquid-filled fibers, integrated optics was implemented almost exclusively in solid-state materials due to the challenges of guiding light through substances with low refractive indices such as gases and liquids. Unfortunately, this has prevented the creation of integrated optical devices and systems for a large class of areas, in particular the life sciences for which fluids (air, water) are the natural environment. It has only been over the past few years that rapid advances in microfluidics, silicon photonics, and integrated optics have converged into the new, burgeoning field of optofluidics, the combination of integrated optics and fluidics in a single system. The groups of Holger Schmidt at UC Santa Cruz and Aaron Hawkins at Brigham Young University have developed a unique approach to optofluidics that is based on creating micron-scale channels that simultaneously guide light and liquids on a silicon chip.
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By Dr. Holger Schmidt The combination of these “liquid-core waveguides� with more conventional solid-state structures creates fully self-contained, planar chips that allow for the study and manipulation of fluids and particles therein with the convenience of off-the-shelf fiber optics equipment. Much of the early work focused on exploration of basic photonic properties such as low-loss light propagation, optical mode structure, and implementation of optical signal processing such as spectral filtering in the liquid-core waveguides. The greatest potential of the technology, however, lies in the application of these devices to fields that historically were off limits for integrated optics, for example molecular biology, medical diagnostics, toxicology, or gas spectroscopy. In particular, the demonstration of optical detection of single fluorescent molecules showed a sensitivity normally seen in expensive and bulky microscopy equipment, and provided much stimulation for new research and applications dealing with single particles on a chip. To this end, the W.M. Keck Foundation supported the creation of the Center for Nanoscale Optofluidics at UC Santa Cruz. Directed by Professor Holger Schmidt, the Center brings together faculty from five different departments (H. Noller, Molecular Biology; M. Akeson and D. Deamer, Biomolecular Engineering; J. Zhang,
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FEATURED PROJECT
S
ingle Molecules on a Chip
PROJECT FEATURED PROJECT
multi-mode fiber
single-mode fiber
Figure 1: Cartoon of optofluidic chip; photograph of chip during experiment; scanning electron images of
Waveguide cross sections with hollow and solid cores along with guided light mode.
Chemistry; and W. Dunbar, Computer Engineering). In this Center, the researchers are able to take an interdisciplinary approach to exploring the use of nanoscale elements in conjunction with optofluidic waveguides to address problems in molecular biology, biophysics, and medical diagnostics. One focus area of research within the Center is the incorporation of nanopores into optofluidic devices. The concept of nanopore biophysics was proposed by D. Deamer who recognized that a molecule passing through a nanoscale hole in a membrane could partially block the opening, and therefore reduce the amount of electric (ionic) current flowing through that hole. Effectively, such a structure functions as an electric, single molecule detector that can distinguish molecular signatures on the picoampere level. Recently, the groups of Professors Schmidt and Noller have demonstrated the first detection of single ribosomes using nanopores that were incorporated into a dielectric layer that comprises the liquid-core optofluidic waveguide. Moreover, they
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were able to control the amount of nanoparticles that entered the fluidic channel by changing the applied electrical voltage. This opens up the possibility to use the nanopores as “smart gates” to introduce individual fluorescent particles into the liquid-core waveguides where they can then be investigated “on demand.” Additional collaborations are under way to apply this principle to quantum dot labeled DNA for genetic analysis and controlled nanopore translocation for DNA sequencing. Another focus area of the Center expands on the theme of particle control. Professor Schmidt’s group has recently developed new implementations of optical particle trapping (i.e., the control over a particle’s motion and position using optical forces). Using the intrinsic optical properties of the liquid-core waveguides, they were able to hold particles in place at any position along the fluidic channel. In addition, they used light beams to accumulate over 100 particles at a single spot within the waveguide, effectively creating the equivalent of an
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PROJECT
Figure 2: Cut-open views of waveguide intersection
with fluorescent particles (green) in light beam (red).
optical leaf blower. Current efforts are directed at using optical forces to create optofluidic devices for particle sorting as well as to examine new trapping paradigms and the potential of moving particles between welldefined chemical microenvironments. A third thrust area deals with single molecule
This snapshot of the research pursued at the Keck Center at UCSC provides a glimpse at the potential of optofluidics. It opens new windows for optical and device engineers to use traditional engineering skills in new contexts that interface electrical engineering with chemists, biologists, toxicologists, and medical researchers. Thus, this emerging area provides an extremely stimulating environment for the development of new optical technology in the years to come. â–
Figure 3: Optofludic waveguide chip with nanopore. Applied voltage is used to drive nanoparticles through Nanopore into fludic channel.
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FEATURED PROJECT
spectroscopy for biomedical applications. The demonstrated ability to detect fluorescent signatures from single molecules opens up the possibility to observe and count individual, labeled bioparticles such as nucleic acids (DNA, RNA) and proteins. These play a central role in molecular diagnostics applied to infectious disease detection, genetic screening, and genomics-based personalized medicine. The ability to identify single molecules on an integrated platform has the potential to break with the current diagnostic paradigm of amplifying the genomic material to create detectable signals. Schmidt’s group is working with a number of clinical researchers to explore the potential of optofluidics as a diagnostic platform.
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Capacitors for High Pulse Current Applications Vishay Intertechnology, Inc. introduced a new multilayer ceramic chip capacitor (MLCC) featuring an integrated resistor and low electrostrictive ceramic formulation. For high-pulse-current applications, the VJ controlled discharge capacitor (CDC) offers excellent reliability, high voltage ratings from 1,000 VDC to 1,500 VDC, and a capacitance range from 33 nF to 560 nF. The integration of a high-capacitance MLCC with a bleed resistor on its surface allows the VJ CDC to discharge more rapidly, while also reducing board space requirements and assembly costs. Typical applications for the device include detonation devices (munitions, pyrotechnics, blasting) and electronic fuzing. The capacitor released today is manufactured in Noble Metal Electrode (NME) technology with a wet build process. The VJ CDC features a low electrostrictive ceramic formulation for repeated charge and discharge cycles, allowing the device to achieve very high field reliability. For more information, please click here.
RF Multi-Measurement Signal Analyzer Agilent Technologies Inc. announced that an innovative, new multimeasurement capability is being added to its 89600 VSA software, enabling simultaneous signal analysis of multiple carriers and signal formats for more efficient testing and deeper signal insight in wireless test. With wireless R&D and manufacturing engineers increasingly working with more than one signal at a time?whether for multi-format/ multi-carrier devices or for viewing both uplink and downlink signals at the same time?analyzing one signal at a time is no longer efficient. Moreover, it fails to provide intelligence about the subtle interactions among dissimilar signals within a device. The 89600 VSA software’s new multi-measurement capability has been engineered to deliver the power of multiple signal analyzers with the convenience of a single, optimized user interface. The software’s advanced architecture will enable engineers to configure multiple measurements simultaneously. For more information, please click here.
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FEATURED PRODUCTS
Stellaris® Robotic Evaluation Board
Get the Datasheet and Order Samples http://www.intersil.com
14-Bit, 500MSPS ADC ISLA214P50
Features
The ISLA214P50 is a 14-bit, 500MSPS analog-to-digital converter designed with Intersil’s proprietary FemtoCharge™ technology on a standard CMOS process. The ISLA214P50 is part of a pin-compatible portfolio of 12 to 16-bit A/Ds with maximum sample rates ranging from 130MSPS to 500MSPS. The device utilizes two time-interleaved 250MSPS unit ADCs to achieve the ultimate sample rate of 500MSPS. A single 500MHz conversion clock is presented to the converter, and all interleave clocking is managed internally. The proprietary Intersil Interleave Engine (I2E) performs automatic correction of offset, gain, and sample time mismatches between the unit ADCs to optimize performance. A serial peripheral interface (SPI) port allows for extensive configurability of the A/D. The SPI also controls the interleave correction circuitry, allowing the system to issue offline and continuous calibration commands as well as configure many dynamic parameters. Digital output data is presented in selectable LVDS or CMOS formats. The ISLA214P50 is available in a 72 Ld QFN package with an exposed paddle. Operating from a 1.8V supply, performance is specified over the full industrial temperature range (-40°C to +85°C).
• • • •
Key Specifications
CLKP
Gain, Offset and Skew Adjustments
VINN
DIGITAL ERROR CORRECTION
14-BIT 250 MSPS ADC
SHA
VREF
OVSS
RLVDS
RESETN
NAPSLP
AVSS
March 15, 2011 FN7571.1
SPI CONTROL
CSB SCLK SDIO SDO
+ –
VCM
• DDR LVDS-Compatible or LVCMOS Outputs • User-accessible Digital Temperature Monitor
Applications • • • • •
Radar Array Processing Software Defined Radios Broadband Communications High-Performance Data Acquisition Communications Test Equipment
SPEED (MSPS)
CLKOUTN
ISLA216P25
16
250
ISLA216P20
16
200
D[13:0]P
ISLA216P13
16
130
ISLA214P50
14
500
ISLA214P25
14
250
ISLA214P20
14
200
ORP I2E
- SPI Programmable Fine Gain and Offset Control - Support for Multiple ADC Synchronization - Optimized Output Timing • Nap and Sleep Modes - 200µs Sleep Wake-up Time • Data Output Clock
RESOLUTION
D[13:0]N
VREF VINP
• Multi-ADC Support
OVDD
14-BIT 250 MSPS ADC
SHA
• Programmable Built-in Test Patterns
MODEL CLKOUTP
CLOCK MANAGEMENT
CLKN
• 700MHz Bandwidth
Pin-Compatible Family
CLKDIVRSTN
CLKDIVRSTP
AVDD
CLKDIV
• SNR @ 500MSPS = 72.7dBFS fIN = 30MHz = 70.6dBFS fIN = 363MHz • SFDR @ 500MSPS = 84dBc fIN = 30MHz = 76dBc fIN = 363MHz • Total Power Consumption = 835mW @ 500MSPS
Automatic Fine Interleave Correction Calibration Single Supply 1.8V Operation Clock Duty Cycle Stabilizer 75fs Clock Jitter
ORN
ISLA214P13
14
130
ISLA212P50
12
500
ISLA212P25
12
250
ISLA212P20
12
200
ISLA212P13
12
130
Intersil (and design) is a registered trademark of Intersil Americas Inc. Copyright Intersil Americas Inc. 2011 All Rights Reserved. All other trademarks mentioned are the property of their respective owners.
Tradeoffs in New-generation
ADCs D
riven by a widening range of high-performance application requirements, Analog-to-Digital Converters (ADCs) are becoming an increasingly pervasive design element, and numerous tradeoffs between performance, cost, and complexity are critical factors for the overall success of product designs. Although there will never be a simple one-size-fits-all solution for ADCs, a number of ongoing technology trends in ADC design now offer designers the ability to closely tailor ADC selection to optimize cost and performance for their specific application requirements. This article is intended to provide an overview of these technology trends, along with some design examples to provide context for understanding the real-
world tradeoffs between different approaches. ADC Trends: Balancing between SNR, Resolution, Sample Rates, and Power ADC designs must achieve an appropriate balance between given performance criterion, such as signal-to-noise (SNR), resolution, and sample rates while also conforming to often very tight power budgets. One overarching trend in ADC capabilities has been the ongoing push for higher resolution and SNR performance at a given sample rate. For example, for 500 megasamples per second (MSPS), today’s newest high-performance ADCs can provide 72.5dB at 14bits compared to previous ADC
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Edward Kohler
Strategic Marketing Manager
Jason Messier
Staff Applications Engineer
capabilities that were limited to 66-67dB at 12-bits. This progress, enabled by the advance of both state-of-the-art design techniques and semiconductor processing capabilities, represents essentially a 100 percent improvement in achievable signal-to-noise ratio, evolving over approximately five years. Another trending axis of improvement has been to increase the available maximum sample rate for a given resolution and SNR. As recently as one year ago, there were only two major ADC vendors offering 14-bit ADCs that provided sampling rates above 155 MSPS. Now, most ADC manufacturers are pushing sample rates to 250 MSPS with 14-bit devices that can deliver 70dB or better SNR performance,
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Low-power operation is also an increasingly critical factor for many ADC applications. This is especially true for handheld devices that must live within a tight power budget as well as for designs that require many ADCs where the combined power usage becomes an important issue. As will be discussed in subsequent sections of this article, the ability to minimize power for a given level of SNR, resolution, and sample rate performance can be the vital linchpin issue in success of the overall product design, and at least one low-power ADC architecture has emerged to meet this need. Another arena of trending change within ADC designs is the variety of interface technologies for getting data on and off the chip. In the beginning, CMOS I/O was sufficient for supporting most applications. However, increasing performance requirements have led to an evolution of faster I/O approaches including DDR, LVDS, Serial LVDS, and potentially SERDES interfacing (While this article focuses primarily on the key performance and power tradeoffs, in a future article we will explore the ongoing ADC interface evolution in more depth).
Scenario #1: Critical Goal: Achieving High SNR and Dynamic Range For many higher-performance applications, the overriding requirement is achievement of the SNR and dynamic range parameters without regard to power usage issues. Prime examples of these performance-first applications are mission-critical military designs such as radar signal processing. Among the key characteristics driving this type of design is the need to deal with both large and small signals simultaneously, and to be able to discriminate both, which requires excellent dynamic range and SNR performance. For instance, in a radar system, strong and weak return signals from both near and distant objects must be processed at the same time with consistent accuracy and speed. If the ADC does not have sufficient dynamic range, then the larger signals will completely dominate the entire range of the converter, and the system will not be able to see the weaker signals. Filtering out the large signals is typically not an option in these types of systems because of the inherently random and changing nature of the signal levels and mix. Another type of application that often falls into this category is high-performance measurement instrumentation, such as signal analyzers. The system designer typically has to create a robust set of capabilities, and a performance window that spans a wide range of signal sensitivity instead of pretailoring the box for a fixed set of
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parameters. Here again, building from the ground up around ADCs with maximum dynamic range and robust SNR characteristics at a high sample rate is the way to enable instrumentation platforms that can provide the widest performance window. Similar challenges exist in many communications applications such as wireless base stations that must distinguish between strong and weak signals to determine proper routing and handoff procedures. In all of these applications, the only option is to design with ADCs that provide the highest possible dynamic range and SNR characteristics at the required sampling rates. One advanced design approach that is proving very useful in these applications is the tight integration of multiple ADC cores that are interleaved using advanced on-chip hardware such as the proprietary Intersil Interleave Engine (I2E). In this approach, hybrid digital/analog background calibration techniques continuously adjust the gain, offset, and sample phase of the multiple interleaved ADC cores, removing inherent manufacturing mismatch as well as adjusting, in real-time, for any mismatches induced by temperature and voltage variations (See Figure 1). Interleaving lower-resolution ADCs at the system level (such as 6-bit, 8-bit, or even 10-bit devices) has become a fairly standard practice, especially for time domain applications where spurious free dynamic range (SFDR) is not a major concern. However, for highperformance applications requiring
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and some are providing a second generation that can deliver over 73dB. Similarly, the maximum sample rate for 16-bit converters has been improved from 200 MSPS in 2008 to 250 MSPS in late 2010 while maintaining SNR above 75dB. This continual improvement in sample rate of high-resolution ADCs is being driven by the increasing resolution and speed requirements of applications such as broadband communications test equipment and advanced medical imaging.
TECHNICAL ARTICLE TECHNICAL ARTICLE
12E: Offset/Gain/Phase Error Estimation and Correction Figure 1: Intersil Interleave Engine (I2E)
converter resolutions of 12-bits and above, interleaving ADCs can become very complex and are best implemented at the chip level. Die-level interleaving of the ADC cores overcomes the dynamic variances in performance that become roadblocks when trying to interleave separate ADCs at higher resolutions. Well-controlled process matching as well as common voltage and temperature characteristics provide inherently better uniformity between the cores that cannot be achieved with separate devices.
compromises on dynamic range, SNR, or robustness.
To achieve nearly perfect matching, the on-chip I2E calibration transparently fine tunes performance on the fly to ensure consistency and to eliminate variances. The real-time adjustments by the I2E make use of arbitrary application sample data to estimate and correct for interleave mismatch of gain, offset, and sample time skew. This enables the multiple cores to perform together as a single high-performance ADC that can effectively multiply the sample rate by the number of cores, all without requiring any
Scenario #2: Need Flexibility for Tradeoffs between Performance, Power, & Design Complexity
As shown in Figure 2, ADC architectures with advanced interleaving can provide the highest levels of resolution, at high sample rates, as compared to Sigma-Delta, SAR, or pipelined architectures without advanced interleaving. For example, Intersil’s ISLA214P50 incorporates two time-interleaved 14-bit 250MSPS ADCs to achieve the sample rate of 500MSPS with SNR performance of 72.7dBFS.
In these situations, the designer typically has some flexibility to approach the application in different ways, thereby enabling tradeoffs in ADC selection between performance, power, and other design considerations. For example, this category includes applications where the signal level might vary, but the variations are either predictable or manageable, such
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that the system could be designed to adjust and accommodate the variability. For instance, a point-to-point microwave communications link between two stations would typically involve less signal variation because it uses focused antennas with minimal blockage between the sending and receiving points. However, signal levels are occasionally impacted by weather conditions (e.g., rain, sleet). This allows for multiple approaches to the system design. One design option would be to use a high-end ADC such as described in the previous scenario with sufficiently wide dynamic range to simply capture and process the diminished signal on the fly. Alternatively, the designer could tradeoff by selecting an ADC with lower dynamic range and using gain control circuitry to adjust the signal path based on weather conditions so that the signal is always provided to the ADC at a consistent level. Of course, the efficacy of one approach versus the other would depend on specific application requirements, such as
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24
Resolution (bits, ~SNR)
22
Sigma-Delta
20 18 SAR
16 14
Pipeline
12
Pipeline with Interleaving Flash
10 8
0.1 0.5
1
5
10
50 100 500 1000 2000
Sampling Rate (MHz) Figure 2: Comparison of ADC Architectures vs. Resolution and Sample rate
the frequency and variability of the signal changes, as well as the power requirements for using a higher SNR ADC versus the external gain control circuitry. Another interesting application in this category could be laser range finders, where a signal of fixed strength is sent out in multiple directions and then both the strength and time signature of the return signals are used to perform distance measurements to create 3D mapping of complex spaces. The signal measurements need to take into account both the surface reflectivity and the distance to the objects being measured. From a signal processing standpoint, a number of design tradeoffs come
into play for such applications. For example, a higher-resolution ADC could be used to resolve the signals more quickly by eliminating the need to average when a lower resolution ADC is used, thereby allowing faster measurements with fewer pulses. With potentially millions of measurements required to map some locations, the amount of time per measurement can be a significant factor. On the other hand, the nature of laser mapping applications can require a certain degree of system portability or even require battery operated platforms for some outdoor applications such as mapping bridge supports. Depending on the specific application requirements,
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a designer might opt for lowerpower, lower-resolution ADCs in combination with external circuitry for averaging the results, or he or she might choose to build the system around higher-resolution ADCs to increase accuracy and speed while minimizing the number of measurements required. For these application areas that require a variety of tradeoffs in ADC capabilities, it can be advantageous to leverage pin-compatible families of devices that give the designer a broader range of choices than with single-point products. For example, a designer that needs to make tradeoffs between resolution and sample rate could start by prototyping with a 14-bit 500 MSPS part and, if needed, could move to a 16-bit 250 MSPS pin-compatible device within the same family without making any changes to the design. Similarly, if the designer needed to tradeoff SNR versus power for a given resolution and sample rate, it is helpful to use a pin-compatible family that provides multiple options. For instance, some families offer multiple performance grades that can provide two or more levels of SNR with the higher SNR coming at the price of increased power consumption. Product designs for increased battery life or higher performance can again be offered without making any changes to the underlying hardware. This flexibility allows designers to tailor and fine-tune the ADC capabilities to meet the specific application requirements without necessitating changes to the overall product design and support
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ADC Architecture vs Resolution and Sample Rate
TECHNICAL ARTICLE
Scenario #3: Minimizing Power Usage is the Critical Factor In this final group of applications, providing ultra low-power operation is the overarching factor for design success. Typical products in this category are handheld devices that need higher bandwidth combined with portability, such as military and law enforcement radios, ultrasonic non-destructive scanners, and
portable cable TV signal analyzers. Sometimes also included in this category are applications where the shear number of ADCs being deployed has a cumulative power usage impact that needs to be minimized, such as some wireline communication systems with thousands of ADCs, where the overall infrastructure’s power budget becomes an important factor. In all of these cases, designers need to have a given amount of dynamic range but must achieve that performance at the lowest possible power level. ADC manufacturers therefore must deliver the performance requirements with ultra low-power
chip level architectures. In addition, the ADC architectures should provide designers with the flexibility to minimize power requirements in the support circuitry and the overall design. A significant step forward in the creation of ultra low-power ADC implementations is represented by Intersil’s FemtoCharge® technology, which fundamentally changes the approach for pipelined signal processing designs. For any pipelined ADC signal processing chain, gain is required between stages. In conventional architectures, signals in each gain stage have traditionally been represented by voltages. In contrast, the FemtoCharge architecture shifts
Traditional ADC
Voltage passed between stages
Stage N
2x gain
Stage N-1
1-bit ADC
2x gain
2x gain
Stage N+1
1-bit DAC
1-bit to DEC
Charge passed between stages
Q V= C
Femtocharge ADC Stage N
2*Cfd
1 2
Cfd
Stage N-1
1-bit ADC
1-bit DAC
Cfd
Stage N+1
1-bit to DEC
Figure 3: Comparison of Voltage-based and Charge-based Pipeline Architectures
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circuitry. The ability to leverage pin-compatible families also opens up options for marketing multiple versions of the same basic product design at different performance levels to meet a broader set of market requirements.
TECHNICAL ARTICLE
In most pipelined ADC designs, the signal must be amplified from stage-to-stage to get the necessary conversion resolution. Voltagebased designs have two limitations. First, signal gain requires an operational amplifier (Op-Amp) and these have high power consumption and limit overall ADC performance due to the dual requirement of high speed and high accuracy. And second, voltage-based designs necessitate that the signal be recreated at each stage. By comparison, charge-based ADCs use the scaling of capacitance to achieve gain from stage-to-stage. In a capacitor, Voltage = Charge/ Capacitance. Therefore the voltage gain needed in each successive stage can be created simply by reducing its capacitance in relation to the preceding stages. And, rather than having to recreate a voltagebased signal from scratch for each stage, in a charge-based pipeline, the original signal is conserved by simply transferring it from one stage to the next (See Figure 3). The FemtoCharge approach enables creation of high performance ADCs with ultra-lowpower characteristics. For example, the ISLA216P25IRZ, a 16-bit 250 MSPS ADC, is the first and only 16-bit converter with a sample rate over 175 MSPS that consumes less than one watt (786 mW at 250 MSPS). Furthermore, a charge-based ADC such as the ISLA214P50IRZ is not only the first 14-bit 500MSPS
converter, but it also provides 73dB of SNR and consumes only 835-900 mW, providing approximately 3dB more SNR at one third the power of its only competitor above 250 MSPS. Charge based designs are thereby giving system designers a whole new set of options for minimizing power without compromising performance. The Bottom Line: More Options Enable Better Design Tradeoffs Although new-generation product requirements continue to escalate and require more demanding signal processing at ever-lower power budgets, the good news for designers is that new-generation ADC architectures are staying ahead of the curve. New advances such as shared-die, multi-core interleaved architectures with transparent on-chip calibration now enable the creation of very high-resolution, high sampling rate ADCs that do not compromise SNR performance, while minimizing design complexity and power. In addition, breakthroughs such as FemtoCharge are enabling even greater power savings by fundamentally shifting the approach to pipelined ADC design.
To begin his career, Edward spent eight years developing high speed, charge domain, analog-to-digital converters and was one of the inventors of Intersil’s Femtocharge technology. He earned his bachelor’s and master’s degrees in electrical engineering at Michigan Technological University and the University of Michigan and his MBA from Yale University. Jason Messier works as a staff applications engineer in Intersil’s high-speed converter group. He holds a BSEE from Northeastern University, an MSEE from Carnegie Mellon University, and an MBA from Babson College. Jason spent eight years in the automatic test equipment industry before joining Intersil in 2006 to design and later support high-speed converters. ■
The bottom line for designers is a much broader set of options to choose from, which leads to better tradeoffs and more effective tailoring of the ADC functionality to meet overall design objectives. About the Authors Edward Kohler is Intersil’s strategic marketing manager for high-speed data converters and ADC drivers.
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the approach and represents signals using electrical charge. This may seem like a subtle difference but in practice, it has major implications for lowering power usage.
©2011 Silicon Laboratories Inc. All rights reserved.
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HEY, YOU!
Get into my Cloud
Rob Irwin
Product Manager
Y
ou know it’s a brave new world when board design and cloud computing get mentioned in the same breath. But it seems that internet-based services and ecosystems—also known as “the cloud”—and electronic devices are colliding with ever-increasing force. Today electronic products have evolved beyond the box that houses the chips and boards, and developed intelligence that transcends their inbuilt logic and programming. Devices are now intimately connected to remote services, and indeed the true value of electronic devices is shifting from the device itself to the online systems that support it.
IDC has predicted that there will be 15 billion connected devices by 2015. Ericsson has put the figure at 50 billion devices by 2020. Whatever the real number, the fact is the market is going to demand a real lot of devices real quick, all of them connected to the cloud and utilizing sophisticated web services to provide functions and features we haven’t even thought of yet.
On the surface it would seem that electronics designers should be able to go about their business largely as usual, connecting components to provide a hardware infrastructure and developing the embedded software that provides the base functionality. After all, the hardware still needs to be built and function. But this value shift has some subtle but profound implications on the industry moving forward.
If we shuffle back in time a little to when analog was king, an electronic system was effectively the board and the components sitting on it. The design engineer’s job was essentially to electrically connect the components in many and varied forms in order to make the electrons flow in useful ways. Fast-forward to the microcontroller era and the job not only involved connecting the components, but also providing the ones and zeros
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The question is, who will create these devices and the ecosystems that support them, and how can they build the systems fast enough? A Problem of Scalability
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TECHNICAL ARTICLE Connecting to other devices Connecting to other ecosystems
Programmable Logic
Embedded Software
Figure 1: Today, the design of the humble PCB encompasses
much more than the fixed components and copper it’s made of, relying on a complex interaction between hardware, software and online services to deliver features and functionality to the end user.
that powered the processor and drove the system—the embedded software. The electronic system had evolved from a purely hardware problem, to a hardware and software problem. What we’re seeing now is the evolution of software development from being a purely embedded prospect, to one that is distributed between the intelligence built into a device and provided by its supporting online ecosystem. As well as that, the hardware itself is moving increasingly to reprogrammable platforms to cope with the rapid and ongoing development of devices beyond their initial release. What we have here is a problem of scalability. The challenges of marrying programmable hardware, embedded software, and web services can all be overcome with our current methodologies given time and suitable engineering and Web development resources.
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To Catch a Thief It’s interesting to reflect that one of the most important enabling elements in building today’s computers is in fact the computer itself. The earliest digital computers were designed with nothing much more than paper and drafting pens. But it wasn’t long before we pressed these basic machines into a service to aid us in building more complex computers. Repeat this cycle a few times and pretty soon you have a billion transistors on a chip and a complex system to support it—all delivered in a neat package with keyboard and mouse for a few hundred dollars. It’s fair to say computer-aided design (CAD) and electronics design automation (EDA) have revolutionized the process of capturing our ideas and turning them into manufactured products. As devices move into the realm of cloud connectivity, becoming far more complex distributed systems than we’ve ever designed before, it’s worth considering whether the cloud itself could provide a possible way forward in bringing scalability to next-generation device design. There’s an old saying that it takes a thief to catch a thief. In this case, perhaps it takes a cloud-based approach to design to build a mass market of cloudenabled devices. Taking EDA Into the Cloud Electronics design tool vendors have often been criticized for lagging the technology that they’re ostensibly charged with enabling. As devices become increasingly internetenabled, and depend more and more on back-end, cloud-based ecosystems to provide critical functionality, this criticism could justifiably be leveled again. That’s not to say EDA tool companies are ignoring the cloud. Many of the chip tool vendors are actively looking to provide some design functions, such as complex verification, as cloud-based services. So indeed, EDA companies are looking at how they can use the cloud as a way to deliver their tools in a more cost-effective and scalable way. While this is, on the surface, a reasonable course of action, it really ignores the bigger issue for EDA vendors when it comes to the cloud.
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But if we’re to get 50 billion devices into production in the next ten years then we really need to radically rethink how we go about taking designs from concept to production.
Connecting to people
TECHNICAL ARTICLE and extend it to the design of device ecosystems. What’s needed is a unification of device and web applications development within a single tool framework. When we start to apply the power inherent in connecting devices and applications to Web-based services and infrastructure to actually developing new, internetconnected devices, we’ll see the ‘internet of things’ really start to take shape.
If we hark back to the computer design example mentioned earlier, simply using the computer as a glorified drafting table (which was essentially the basis
Cloud-Based Design for Everyone
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Design tool company Altium has launched its AltiumLive online portal that connects directly to its Altium Designer software and Design Vault technology to bring web services directly into the electronics design space. Figure 2:
of first board design programs) didn’t really raise the abstraction level at which we could design. It just let us do what we’d always done, only a bit faster and more conveniently. It wasn’t until we used the computational power and logic available to automate processes and help make and enforce design decisions that we were able to move forward at the pace necessary to make the digital age a reality. Similarly, electronics designers today need tools that allow them to harness their device design experience
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A simple example of the power of device-to-cloud connectivity is the way Amazon’s Kindle book reader system synchronizes itself across multiple platforms. Regardless of which device you use—Kindle for PC, Kindle for iPad, the Kindle device itself—when you open any device you’ll be presented with the last page you were reading, regardless of which device you were last reading it on. Amazon uses a person’s Kindle account in the cloud to transparently synchronize this information across all devices in the ecosystem. Now Amazon is a large company with huge resources available, so it has the ability to push through the development of such a system with the tools currently available by gathering together hardware, software and web development teams, each working within their individual realms of expertise. But imagine if cloud connectivity and a range of cloud service building blocks and templates were standard parts of an electronic product developer’s design tool. And imagine if the design environment on the designer’s desktop was part of a larger, cloud-based ecosystem that provided automatic hosting and deployment services (among other things) that allowed designers to connect the devices they design directly to the cloud and utilize the services they create. With such a system, even developers with limited resources could bring the potential of cloud-based services and functions directly and easily to their products and the people using them. The Shape of Things to Come One could argue that the entire history of solid-state electronics has been one of unification. Multiple transistors were brought together on a single piece of silicon. Functional circuit blocks have been combined to create large-scale integrated circuits. Software has been
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It’s not really about tool vendors using the cloud to simply provide the tools and services they currently offer in a better or more efficient way. The real game changer comes in the broader product development arena, and it will happen when the tool vendors ask themselves one simple question: How can they use the cloud to help their customers design for the cloud, and not just design the devices that connect to it?
TECHNICAL ARTICLE
Today we’re reaching another technological turning point, and once again we need to unify processes and evolve the tools in order to progress. A number of companies and products have demonstrated the power of connecting devices to Web-based ecosystems. Increasingly, this cloud connectivity is automated and does not require human interaction. As we move forward, cloud connectivity will be a necessary part of all devices across the spectrum of markets from consumer and industrial through to military. This will happen because the potential of ubiquitous device connectivity is too great to ignore, similar to past state changes such as the digital and embedded software revolutions. For engineers and designers this will mean changing their mindsets to incorporate online components directly
Design Space
into the hardware and embedded design process right from the start of a project. For tool providers it means finding ways to utilize the cloud to provide “plug and play” access to online services, real-time connections into supply chain and manufacturing information via the web, and an expanded definition of design components to include functionality provided remotely to hardware devices via back-end, online ecosystems. Whichever way you look at it, electronics designers and engineers are headed for the cloud. The real question is, when they get there will they be able tap into that silver lining? About the Author Rob Irwin has a Bachelor of Engineering (Electrical) from the University of Sydney, Australia. He has over 20 years of experience in the electronic design industry including several years as editor of Australian Electronics Engineering. Rob currently holds the position of Product Manager at Altium Limited. ■
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Design tool company Altium’s Vault technology uses web-based services to connect components in the design space to the wider supply chain, allowing designers to get real-time price, availability, and other information on parts as they use them within the Altium Designer software. Figure 3:
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unified with hardware to create programmable platforms. At each stage, the technology and the tools have evolved to raise the level of abstraction at which we can work. It’s this principle that has allowed us to achieve the many orders of magnitude increase in system complexity in the relative short lifetime of the industry.
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