EEWeb Pulse - Volume 22

Electrical Engineering Community

Allan EvansSamplify Systems, Inc.

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PULSE EEWeb.comIssue 22

November 29, 2011

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TABLE O

F CO

NTEN

TSTABLE OF CONTENTS

Allan Evans 4Vice President of Marketing, Samplify Systems, Inc.

Ultrasound Beamforming 10Development KitBY ALLAN EVANS

Featured Products 11

Handling Clocks in Software 13BY DAVE LACEY WITH XMOS

Focus on Sensor Design 17BY STEVE KOLOKOWSKY AND TREVOR DAVIS WITH CYRPESS

RTZ - Return to Zero Comic 22

A description of Samplify’s new Ultrasound Beamforming Development Kit.

Interview with Allan Evans

An introduction to the basics of software-based clocks.

Discover the technology that makes today’s touchscreens work.


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Allan Evans Samplify Systems, Inc. How did you get into electronics/engineering and when did you start?My dad came home one day with a Radio Shack TRS-80 Model 1 computer when I was in fifth grade. It had four kilobytes of RAM. I tell my kids that back in those days, when we wanted to play a game on the computer we had to actually type it in ourselves and save it on cassette. I was hooked on the computer. I remember when my dad went out and got a RAM update from four to 16 kilobytes, which at that time was more RAM than anyone could possibly need.

It is neat how times have changed.

I went to college at the University of California, San Diego to study electrical engineering and earned my Master’s degree. After working for a couple of years and recovering from graduate school, I decided to go back and get an MBA. I did the night school thing at Santa Clara University.

What are your favorite hardware/software tools?My hardware days are behind me, but I recently had the opportunity to use Agilent’s LTE test suite

for our CPRI compression technology, and I was amazed at the capabilities.

For software I still use MATLAB a bit.

What is on your bookshelf?A friend recently gave me Inbound Marketing by Hannigan and Shah, and it really makes sense of how to combine outbound marketing with inbound marketing via Google and social networks.

Do you have any tricks up your sleeve?As you switch from engineering to marketing you have to learn that your job is now to define problems, not to provide solutions. Any company will have talented engineers who can come up with elegant technical solutions, but often they fall into the trap of not having defined the right problem.

Where did you go to work out of school?I went to work for a company called Stanford Telecom, which, among many other inventions, created GPS technology. It was acquired in the late 1990s by Newbridge Networks, which has since been

Allan Evans - Vice President of Marketing, Samplify Systems, Inc.


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acquired by Alcatel.

Right out of school I started as a hardware and DSP engineer. For eight years I worked at Stanford Telecom on satellite transponders for NASA. NASA would use them for high-altitude weather balloon experiments. This was interesting because about two years ago, a NASA employee stopped by our booth and talked about how they are still using these transponders. Thinking back to how many green wires there were going across the boards, and the difficult life of these transponders, I was amazed to see that 18 years after I worked on them, many of them are still being used. When the balloons come down they do not come down very gracefully, and can end up all over the place. I was just amazed to hear that they are still in operation.

The last project I worked on at Stanford Telecom was a broadband wireless system. This was really in the days of WiMAX, before WiMAX was WiMAX. That was ultimately the product line that Newbridge acquired from the company. I went on to another broadband wireless company called Netro. In 1998 Netro had a billion dollar IPO based on quarterly revenues of $18 million. It was perfect timing for me.

At Netro I was working on systems providing broadband wireless and T1 replacements for mostly small and medium-sized enterprises that only needed a couple of megabits per second Internet access. Technology allowed us to do ATM over the years, but you do not hear much about that anymore.

IP eventually took over all of this. This was really when I transitioned into marketing for the first time. When I joined Netro I was the director of product marketing for the broadband wireless product

...as you switch from engineering to marketing you have to learn that your job is now to

define problems, not to provide solutions.

Any company will have talented engineers who can

come up with elegant technical solutions, but often times they fall into the trap of not having defined the right problem.

line. They just introduced a first-generation system. Typical of a startup, it kind of missed the mark in terms of what the market required. I came in and defined a couple of critical features that

the wireless operators are looking for to make it truly a carrier class. At that point we signed a system integrator relationship with Lucent and that really paved the way for the IPO.

After Netro, where did you go?I worked for Netro for five years, and then worked on my own start-ups. At the end of my tenure at Netro, I was doing business development, and that culminated in the acquisition of the project Angel Technology from AT&T Wireless. That was a fixed and mobile wireless technology, also before WiMAX was WiMAX. But at the time the market had crashed, Netro’s stock was trading below cash value. The investors wondered why we were making acquisitions in a financial position where we could not give any forward guidance. So after that, Netro sold itself to another company, SR Telecom. They are still carrying on with the technology.

In 2003, it was a challenging environment to try to launch a start-up company, especially one that relied heavily on semiconductor business models. So after a couple years of that, I went to work for a company in the RFID field, Savi Technology.

Savi specialized in active RFID, so these were battery-powered tags. The biggest market for this particular RFID technology was freight containers shipped through the global supply chains. Other applications are asset tracking and drive applications. It is a


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challenge to track items at pallet levels instead of containers. There are a whole bunch of issues, such as who bears the cost. Basically, if the wooden crate costs less than five dollars to build, the issue lies in who is going to pay for any electronics attached to the crate, and who pays for the rest of the infrastructure. These are the kinds of things that people are still working out. In terms of tracking freight containers, it turns out that the largest shipper of freight containers in the world is the U.S. Department of Defense. They use a combination of Navy ships for critical items, but also commercial shippers as well. Everything comes in through Navy-operated Port terminals. It is a supply chain where they have control over each of the checkpoints. It was a very good model to start with because it is an integrated supply chain that a customer can put together and control all the places where infrastructure can be installed.

In 2006, an RFID company down in Morgan Hill, California called Alien Technology filed for an IPO. When it put out its S1, its revenues were 50 percent of the cost of goods sold. When all of the financial analysts went through it, all of the press started saying “It’s 1999 all over again.” Evidently that has not stopped a lot of the social networking start-ups these days but five years ago that pretty much killed IPO as an exit strategy for the RFID market. So Savi ended up being acquired by Lockheed Martin.

I worked at Lockheed Martin for a year, and now I work for Samplify

going to use it? Everyone in the room looked at me and said, “Allan, don’t you realize that is why we hired you?” So it turns out that the ADC was really ideal for the medical ultrasound market. In the probe of an ultrasound machine there can be up to 256 individual ultrasound transducers that convert electrical waves to acoustic waves. Each one of those is connected via a micro coax cable back to an ADC channel sitting in the console. The ultrasound machines use a very large number of ADCs, so when we brought ours to market it had twice the number of channels and half the power of other solutions in the market. It also integrated our signal compression technology, which reduced the number of pins to get the data off the data converter by 60 percent. Routing all of that stuff into an FPGA is also a challenge.

What is the current business model that is doing better?The IP sales are doing better. The compression technology is what I call a horizontal market. We announced an agreement about a year and a half ago with a company called Moog, which supplies slip ring devices to medical imaging companies, and we have found a lot of different applications with Moog. All of the x-ray detector technology rotates around the patient, and there can be 10 to 100,000 x-ray detectors spinning around the patient. Each one of those is connected to an ADC. By the time you aggregate all the data that is collected from the detectors, it amounts to 10 GB per

Systems. So the joke at Samplify is that we hired our V.P. of Marketing away from Lockheed Martin. I have been at Samplify for just over four years. The company was launched in March of 2007 and I joined in May of 2007.

When Samplify first launched, what was the initial product line?The core technology for the company is our prism signal compression technology. Trying to launch as an IP company is very challenging unless you have some real immediate attraction and a way to get to tens of millions of dollars in revenue very quickly. Because our compression technology operates on any signal that originates in the analog domain, it tends to provide more value to a system when you put more compression to the analog domain and decompression to the software domain. We thought of integrating the signal compression technology with data converters, and that was the business model that got the company our Series A funding back in March of 2007. But from March 2007 to October 2008 we were kind of a stealth-mode semiconductor company and presented ourselves as an intellectual property company around the compression technology. I remember we had a kick-off meeting in early June, just a couple of weeks after I arrived, and our analog designer said “I am going to build you this 12-bit, 65-megasample ADC. I think I will be able to pack 16 channels of this onto one die.” It sounded interesting but where were we


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second. So this was an easy thing for us to do with our compression IP without having to integrate it fully with a data converter. By partnering with Moog, we were able to eventually wrap our IP in a couple hundred pounds of spinning aluminum. This gave us a great way to penetrate the market. About a year ago we announced a deal with Integrated Device Technology (IDT) around our compression technology for wireless infrastructure applications, particularly cellular base stations. Now with the deployment of LTE, the radio units are connected through fiber optic cables, and the capacity can be 10–20 GB per second. We can be anywhere between a 33 to 50 percent reduction in terms of capacity.

We are looking for new markets to get into lately. We have been getting a lot of interest from high-speed and high-resolution imaging applications. We also closed our Series B round of funding and one of the investors was Schlumberger, who does oil and gas exploration, and we just announced our Prism FP technology, which extends our compression from integer data types. This has been historically how it is used after it comes out of a data converter, but now we do floating point as well. This allows us to move out of the data acquisition side of these systems and into the data center and data processing. This opens up a lot of applications in terms of high-performance computing application, supercomputing, and cloud computing.

The ultrasound market, though, has really been our specialty over the last three years since the introduction of our SAM1600 family of ADCs. When you build a data converter, it gives you a unique insight into the entire signal chain on our system, and based on this we started working on ultrasound beamforming technology about three years ago.

We always have many exciting

activities going on at Samplify. What I am most excited about right now

is our ultrasound beamforming

technology.

Over the last few years we have found that the ultrasound market is very fragmented. Even the big three manufacturers, GE, Phillips, and Siemens, have almost a dozen different machines filling different niches in the market. Whether it is cardiology, general purpose radiology, OB/GYN, portable emergency rooms, or ambulance types of applications, there is really a wide range. And since announcing our beamforming development kit last October, we have been amazed at how much

the market is fragmenting even further. We have lots of companies who want to combine ultrasounds with different technologies, like endoscopes or specialized cardiology stuff where their competitive advantage is in an algorithm and they really want to be able to buy the ultrasound technology off the shelf. We also sell it as a development kit to allow manufacturers to essentially rapidly develop new machines. So instead of taking three years to get to market for a new machine, they can get to market in 12 months because from day one they have a development kit on which they can start developing their software and not have to wait another six to nine months for their hardware guys to get every last piece of noise out of the analog signal chain.

Is the company going to be getting into the medical field?Our intentions are to be a provider of components and subsystems of IP to Ultrasound system manufacturers, as well as other application areas. It is a horizontal technology. We are doing the heavy lifting on the analog side of the design to enable them to make ultrasounds cheaper and more effective. We have no intentions of become a supplier of medical equipment.

We learned a valuable lesson as a start-up company. When we closed our Series A in March of 2007, we closed our Series B in January of 2011. That means that we somehow survived the financial crisis in-between. We did so by not being solely focused


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on a particular business model. Sometimes when you are a start-up you are looking forward to your next round of funding, it is kind of like when you remodel your kitchen. You pick your appliances based on what the people who are going to buy your house from you will want, not what fits your own lifestyle necessarily. It is kind of the same way with start-ups and their business models. For a long time we were trying to stick hard to a position of being a pure-play semiconductor company, and as we started getting designs in with our ultrasound customers we really began to realize that a lot of these OEMs needed the technology provided to them with a higher level of integration, in the form of modules or subsystems. We adapted to the needs of the market and we did not really stick dogmatically to “no we are only a semiconductor company, we can’t do that,” and that has turned out to be a very successful strategy for us in terms of engaging customers in this fragmented market.

What is involved in the design of ultrasound systems?We have spent several weeks in our customers’ labs helping them bring up their analog designs around our components. So yes, it is very support intensive. But then you get the benefits afterwards of long product lifecycles because these machines stay in production for three to five years.

When you look at our website you see a lot of different product forms, from the chips to the modules to IP to subsystems. That is really

what we pride ourselves in now, making our technology available to customers in whatever form they want to buy it.

When it comes to your IP for your compression, do you typically work with TI DSPs, or is it FPGA-based, or basic hardware?All of the above. The technology is available in software form, so it runs on Intel CPUs, DSPs, anything with a C Compiler. But we also make it available in RTL form to run on any FPGA family.

Do you have any note-worthy engineering experiences?I have been lucky enough to have had two parts in projects/companies where I had a major role. For the first I was in an engineering management role from the very beginning, and the product line was sold for over 300 million dollars. For the second, I came in to a marketing role and defined the second generation of a product line, which enabled the company to have a successful IPO at over a one billion dollar market cap.

What are you currently working on?We always have many exciting activities going on at Samplify. What I am most excited about right now is our ultrasound beamforming technology. We are introducing a second generation of our beamforming development kit which gives an OEM everything needed to start developing an ultrasound machine. We have

received a lot of interest not just from our OEM customers, but also from other partners in the value chain who want to be a part of the ecosystems.

What direction do you see your business heading in the next few years?Samplify will be strengthening its core intellectual property base and delivering solutions around it to customers.

What challenges do you foresee in our industry?As a small company trying to sell into the medical equipment, wireless infrastructure, and computing markets, it is challenging to get the large suppliers to adopt our technology. We have addressed this by pursuing strategic partnerships with other companies in the value chain, like Moog who makes slip rings for CT machines, and IDT who is a leading provider of semiconductors for wireless infrastructure. If you are not a social networking start, then seeking strategic partnerships is a key strategy for a start-up to get to market. ■

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PROJECTFEA

TURED PRO

JECTUltrasound Beamforming

Development KitBy Allan Evans

Samplify is the first company to offer ultrasound beamforming technology and products to medical

imaging equipment manufactuers. Traditionally, the OEM had develop this key signal processing technology internally, resulting in long development cycles and costly R&D expenditures. With the ultrasound market rapidly fragmenting in many specialties, it is becoming difficult for even top tier OEMs to maintain their R&D investments across all of the platforms they must keep in their portfolio to be competitive in all of the segments: traditional radiology, cardiology, OB/GYN, emergency room, surgical, even veterinary. Samplify’s ultrasound beamforming development kit provides the OEM out-of-the-box with everything it needs:

• 64 channel analog front end with continuous-wave Doppler support

• Support for up to 192 element probes with phased array, linear, convex, or array configurations

• Samplify’s award-winning AutoFocus™ beamforming technology with QuadBeam™ processing

• Mid-processing support for B-mode, color flow, pulse Doppler, power Doppler, CW Doppler, harmonic imaging

• Single 12V power supply

• USB or PCIe interfaces to Windows or Linux PCs

• Samplify’s Ultrasound API which provides a high level programming interface to configure probes and beam steering patterns.

• Demonstration imaging software

Many OEM customers are adopting this platform to directly integrate into their systems, enabling them to only provide industrial design and software. For OEM customers who want to customize the design to their production form factors, we also can provide a manufacturing license and supply to them the schematics and layout files. What makes this exciting is that we are giving these OEMs go-to-market options they previously did not have. If they wanted to integrate ultrasound technology into their systems, they either had to design from scratch from a bag of parts or resell an existing black box machine with no ability to customize it. With our beamforming development kit, the OEM can fully customize his hardware and software, without the long development cycles of designing from a bag of parts. ■


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mounted on state-of-the-art 4-layer PCBs, its thermal performance matches much bigger standard SMD packages and allows Ptot levels of up to 1.1 W in a tiny footprint. Driven by miniaturization in chip design, NXP’s ultra-compact medium power transistors offer design engineers a flexible power transistor solution for designs focusing on space saving, energy efficiency, and low heat dissipation. All NXP medium power transistors are automotive-qualified according to AEC-Q101.For more information, please click here.

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14-Bit, 500MSPS ADCISLA214P50The 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• SNR @ 500MSPS

= 72.7dBFS fIN = 30MHz = 70.6dBFS fIN = 363MHz

• SFDR @ 500MSPS= 84dBc fIN = 30MHz = 76dBc fIN = 363MHz

• Total Power Consumption = 835mW @ 500MSPS

Features• Automatic Fine Interleave Correction Calibration• Single Supply 1.8V Operation• Clock Duty Cycle Stabilizer• 75fs Clock Jitter

• 700MHz Bandwidth

• Programmable Built-in Test Patterns

• Multi-ADC Support

- 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

• 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

DIGITALERROR

CORRECTION

SHA

VINP

VINN

14-BIT250 MSPS

ADC

CLOCKMANAGEMENT

SHA14-BIT

250 MSPSADC

CLKP

CLKN

SPICONTROL

CS

BS

CLK

SD

IO

VREF

OV

SS

AV

SS

AV

DD

CLKOUTP

CLKOUTN

D[13:0]P

D[13:0]N

ORP

ORN

OV

DD

CLK

DIV

NA

PS

LP

SD

O

+–VCM

RES

ETN

VREF

I2EGain, Offsetand Skew

Adjustments

CLK

DIV

RS

TP

CLK

DIV

RS

TN

RLV

DS

Pin-Compatible Family

MODEL RESOLUTIONSPEED(MSPS)

ISLA216P25 16 250

ISLA216P20 16 200

ISLA216P13 16 130

ISLA214P50 14 500

ISLA214P25 14 250

ISLA214P20 14 200

ISLA214P13 14 130

ISLA212P50 12 500

ISLA212P25 12 250

ISLA212P20 12 200

ISLA212P13 12 130

March 15, 2011FN7571.1

Intersil (and design) is a registered trademark of Intersil Americas Inc. Copyright Intersil Americas Inc. 2011All Rights Reserved. All other trademarks mentioned are the property of their respective owners.

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Dave LaceyTechnical Director of Software Tools

Handling Clocksin Software

Clocks are standard concepts for hardware designers but less familiar to software engineers. However, in embedded programming (and particularly real-time embedded programming), software developers have to handle clocks in their software programs. This article discusses the basics of software-based clocks.

What Makes a Clock

A clock is a signal that alternates with a fixed frequency.

The period of the clock is the time between consecutive rising edges of the signal. The frequency is the rate at which rising edges occur (i.e., 1/period). The period or

frequency characterizes the clock. In software, to keep track of a clock you need to store just one of these values. In this article, the examples characterize the clock with its period because this makes them easier to code. For the sake of exposition, let’s use a floating point type for representing it (e.g., the C double type). In practice, any type that can represent time can be used. A fixed point representation is often used.

Using a Clock

Once a clock frequency is available in software, you can easily multiply or divide the clock simply by multiplying or dividing the period. The information about the clock

Figure 1: A clock signal.

Time

Clock

PeriodFallingEdge

RisingEdge


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can be delivered to a remote system to recreate remotely, or to control a stream of data that is to be transported in sync with the clock.

Outputting a Clock

To output the clock you need to bit-bash an output port alternately high and low. The following C-style pseudo-code shows the idea:

Here get_current_time gets the current time and output_at_time outputs a value to a port at the specified time. However, these functions are only accurate to some resolution inherent in the software system. The frequency of the output clock is quantized to that resolution, meaning the frequency can be quite far off the required value. You can improve this by keeping track of the error caused by this quantization and adjusting as you go along. The following code shows this:

This algorithm keeps track of the error and when the error gets big enough to incorporate into the output it does so. With this method the output clock will have the correct frequency but the quantization will still cause an observable jitter on the clock.

Recovering a Clock

Sometimes you need to recover the clock from an incoming signal so you can use it as a base for other processing in the system.

Matching the Frequency

The simplest thing to do is match the frequency of the incoming clock. Over a particular period, count the number of rising edges of the clock and then calculate the period per rising edge:

The incoming clock varies its frequency over time so you have to re-sample regularly.

Using a Feedback Loop

Sometimes just matching the frequency of a clock is not enough. The small mismatches and adjustments add up over time causing your internal notion of a clock and the actual clock to drift over a long period. The number of ticks from the recovered clock can be different to the number of ticks of the original clock.

To cope with this you need to continually adjust for the accumulated error between the clocks—a task that can be done using a PID control loop 1.

Supposed you want to match an outgoing clock to an incoming clock. The idea is to adjust the outgoing clock period at regular intervals. At each adjustment point, look at the number of ticks since the last adjustment of the incoming clock (ticks_in) and the number of ticks since the last adjustment of the outgoing clock (ticks_out). The difference between these is the proportional error of the clock.

From the proportional error, you can also calculate the integral (or accumulated) error and the differential error. The period is then adjusted based on these values to move the clock period toward the correct value. Over time the algorithm homes in on a fixed point and the proportional error tends towards zero. The following code can be used to adjust the period at each update (see Figure 5).

Figure 4

Figure 2

double t:int val = 0;t = get_current_time();while (1) { t += period/2; output_at_time(t, val); val = ~val;}

Figure 3

double t:int val = 0;double hi = floor((period/2)/resolution)*resolution;double lo = (period/2) - hi;double err = 0;

t = get_time();while (1) { t += hi; if (err >= resolution) { err -= resolution; t += 1; } output_at_time(t, val); val = ~val;}

period = sample_period / ticks_in;


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The setting of the constants Kp, Ki, and Kd affects how quickly the algorithm will settle and how much perturbation in the input clock it can handle. There is a trove of methods on calculating these constants correctly for your application, which are not discussed here, but a good starting point is the Wikipedia page on PID control loops.

The following graph shows a typical progression of the error of such an algorithm over time. (See Figure 6)

Why?

To a hardware engineer the outcome of the previous section is hardly outstanding. A clock has been routed in a rather complex manner. So why do you need to bring clocks into the software domain? One reason is that with the clock as a logical entity in software, you can analyze it and manipulate it. For example, you can fractionally multiply the clock to be used elsewhere or you can report its frequency to some higher-level application.

However, one big application is that you can transmit a clock to another part of the system and recover it via a digital-only transport without the need to explicitly transport the clock. For example, the clock can be

transported over a USB bus or an Ethernet network. This brings a wealth of benefits in terms of connectivity and flexibility that would be severely limited if you had to explicitly connect every clock signal in the system.

To recover a clock remotely you need to transmit the feedback information (e.g., the tick counts). This counting over a period of time still requires a common timebase, so all parts of the system must have the same sense of global time. How this is done is outside the scope of this article, but for bus-based systems (such as USB or Firewire) the bus may carry a global clock. For more loosely coupled systems such as Ethernet or other packet-switched networks, a global clock recovery protocol is required such as IEEE 1588. 2.

References:1 http://en.wikipedia.org/wiki/PID_controller2 http://en.wikipedia.org/wiki/Precision_Time_Protocol

About the Author

Dr. David Lacey works as Technical Director of Software Tools at XMOS Ltd. With over ten years of research and development in programming tools and compilation technology, he now works on the development tools for XMOS devices. As well as tools development, he has worked on application development for parallel and embedded microprocessors including work in areas such as math libraries, networking, financial simulation, and audio processing. XMOS Website. ■

Figure 6: PID Error Progression.

P = ticks_out - ticks_in;I = I + P;D = P - prevP;period = period + Kp * P + Ki * I + Kd * D;

Figure 5

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Focus onSensorDesignLet’s Take Apart aTouchscreen Phone!

Steve KolokowskySr Member of the

Technical Staff

Trevor DavisDirector of Marketing

& Applications

Everyone likes to break things on occasion—it’s fun! And some of us really like to tear open electronic devices just to see what’s inside; of

course, it’s even more fun when you don’t have to worry about putting it back together. With today’s consumer electronic devices, taking a product apart can virtually guarantee that it will not go back together, so few people really know what makes up the touchscreen system. In order to understand one of the hottest technologies on the planet, however, it is imperative that we peel back the top layer on a touchscreen phone to see what is inside. Once we do, we’ll discover the technology that makes today’s touchscreens work.

While all consumers can see the outside of today’s hottest cell phones and can see that many of them have a plastic or glass display, most people don’t understand what is underneath and why. We will explore the design and construction of the product sensor, the invisible technology that senses an on-screen finger touch, and even some of the technical tradeoffs that mobile product manufacturers must make when designing a touchscreen product.

It’s also worth noting that this particular article will be the first in a series of three articles that will help readers understand the engineering design and construction of a touch product, how the onscreen touches and gestures are registered and interpreted by the product, and finally, how consumer products make the use of stylus possible on touchscreens. All of these articles are designed to provide a technical understanding of the detailed pieces of the touchscreen subsystem.

Touch technology begins in the most obvious places: with the finger. Regardless of the technology type used in a particular touchscreen, the finger provides a disruptive component to the system. Some touchscreens are designed to use the physical force of a touch to register a touch, other technologies rely on the finger to be a disruption to infrared or camera field of view, and still others measure the physical change in electrical current as a result of the introduction of a finger. It is this final technology that we will focus on for the majority of this article. The measurement of change in electrical properties of a touchscreen panel is called “capacitive touch” technology. In this case, the touchscreen


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system is capable of measuring the minute changes in capacitance present in a touchscreen.

In fact, the projected capacitance sensing hardware consists of a glass or plastic top layer followed by an array of X and Y sensors composed of ITO deposited on an insulating layer. ITO is a transparent conductive clear material that is capable of carrying a charge both to and from the touchscreen surface. Specifically, electrical charge is measured on a touchscreen through intersecting channels of transmit and receive electrodes, typically arranged in a row and column pattern to easily determine where a disruption occurred.

As a finger or other conductive object approaches the screen, a capacitor is formed between the sensors and the finger. This capacitor is small relative to the others in the system, but it is measurable by several techniques that typically involve rapidly charging an in-circuit capacitor and measuring the discharge time through a resistor. Two sensing types are commonly used: “mutual capacitive” and “self-capacitive” sensing. Self cap senses the increase in self-capacitance of a sensor as a finger touches the screen. Mutual cap measures the decrease in capacitive coupling between a transmit sensor and a receive sensor (also shown in Figure 1).

Figure 1: Finger conductivity disrupts electrical field on touchscreen (mutual capacitance type sensing).

Figure 2: Mutual and Self Capacitance Measurement in a Capacitive Touch System

A projected capacitive sensor array is designed so that a finger will interact with more than one X sensor and more than one Y sensor at a time. This enables software to accurately determine finger position to a very fine degree through interpolation. Because mutual capacitive sensing examines every x/y intersection instead of simply examining each x/y sensor, mutual capacitive sensing can detect many contacts simultaneously.

Now that we have the basic concept of why a finger can be a disruptive contributor on a touchscreen, let’s further explore the physical hardware in a touchscreen system and understand the contribution each component makes to the overall system.

Figure 3 shows several key components that include the coverlens and sensor, the LCD, and the Printed Circuit Board. The coverlens is the outward facing component of the product. This is where the consumer interacts with the product. In some products, this coverlens could simply be a protective cover to prevent scratching and damage, or it can actually be part of the touch sensing system itself. In most capacitive touch systems, a touchscreen “sensor” sits just below the coverlens. The sensor is a clear glass or acrylic panel with a touch-responsive surface printed or deposited on it; this sensor is then often directly adhered to the coverlens itself. Next, the touch sensor is placed over a graphic display so that the touch area of the panel covers the viewable area of the screen. The last key component to the hardware system is the touch controller itself. In today’s systems, the touch-controller is a small microcontroller-based chip like the Cypress TrueTouch™ that is placed between the touch sensor and system’s host controller. This chip can either be located on a controller board inside the system or it can be located on a flexible printed circuit (FPC) affixed to the glass touch sensor. This touch-controller

Electrical Disruption

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MUTUAL CAPACITANCE SENSINGBaseline capacitance prior to touch

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takes information from the touch sensor and translates it into information the system’s host controller can understand, and sends the information over a common communication bus such as I2C or SPI that requires only five to eight pins to connect over the flextail connector to the main PCB (see Figure 4).

While the description above provides the basic breakdown of the system, let’s explore the technical details of the touch sensor itself. Figure 3 shows a blowup view of the sensor cross section that shows the layering of multiple different conductive materials. Depending on the pattern and materials chosen for the sensor, there are many different combinations of ITO layering, film or glass substrates, and interleaving adhesive (OCA: Optically Clear Adhesive) materials. These combinations are chosen to allow a manufacturer to tradeoff between thickness, cost, transparency, rigidity, bezel width, front window material, weight, and performance.

Most touchscreen sensors are then directly bonded to a liquid crystal display (LCD) or the newer Active Matrix Organic Light Emitting Diode (AMOLED) technology

Figure 3: Touchscreen System Components.

Figure 4: Various Touch Panels with different manufacturing configurations.

using an Anisotropic conductive film (ACF) that uses tiny conductive metal spheres on the adhesive tape to bond the touchscreen panel to the LCD module. Displays for a touch-enabled product should be chosen for the same reasons they would in a traditional system: resolution, clarity, refresh speed, and cost. One major consideration for a touchscreen, however, is the level of electrical emission, or “noise” it produces. Because the technology in the touch sensor is based on small electrical changes when the panel is touched, an LCD that emits a lot of electrical noise can be difficult to design around.

There are several LCD types that are common in consumer products and must be carefully considered for design-in:

Dot Inversion

For a touchscreen, this is the preferred TFT LCD display technology. The dot-inversion type LCD has a DC common voltage (DC Vcom) covering the surface of the LCD. The DC Vcom acts as a shield for the inherent switching noise of the LCD.

Coverlens & Sensor

Printed Circuit Board

LCD

Glass CoverlensITO Layer(s)Glass or Film Substrate

Flexible Printed Circuit (with touch controller)

Full Touch Assembly: Sensor, Coverlens, Flextail, Touchcontroller

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Line Inversion & Frame Inversion

The line-inversion type LCD has an AC common voltage (AC Vcom) covering the surface of the LCD. This AC voltage generates noise that is picked up by the sensors. This type of LCD requires a third layer of ITO, the shield layer, that protects the receive electrodes from the noise from the LCD switching. If this type of LCD is selected, it is important to select the slowest possible signaling rise time as switching frequency directly relates to how much noise is created by the LCD.

AMOLED

AMOLED consists of a matrix of OLED pixels that generate light from a continuous current flow controlled by at least two thin film transistors (TFTs) at each pixel. One TFT is used to start and stop the charging of a storage capacitor and the second TFT is used to provide a voltage source necessary for a constant current. This construction allows for very low noise profiles, and is ideal for capacitive sensing systems.

Finally, when a finger touches the touch sensor, the electrical change is carried off panel through the receive electrodes and the change in capacitance is measured by the touchscreen controller. Based on the noise emission from the LCD, the touch controller will have a harder or easier time differentiating a true touch from an interference signal. It is at the touchscreen controller chip that the real effectiveness of the other hardware in the system is discovered. If the panel has a resistivity that is too high, if the LCD emits too much noise, or if the pattern design is imprecise or not optimized for performance, then you will have very weak or inaccurate signaling returning from the touchpanel to the touch controller.

Programmable solutions like Cypress Semiconductor’s

TrueTouch™ family provide on-chip mechanisms for filtering noise and for compensating for poor signal. Depending on the particular device architecture, the analog in the system may be reconfigured to integrate signals over longer time periods to filter noise. Different signaling frequencies, including spread spectrum and pseudo-random frequencies can be used to avoid noise. Standard digital filters can remove one to two-bit signal jitter or provide a low-pass filter like an IIR. Smart digital filters can discard samples that don’t “look right” compared to the samples near them on the panel. Smart filters are limited only by the system designer’s ingenuity. All of these controller techniques are simply ways to manage or compensate for signal errors that return from the touchpanel. Clearly, from the design discussion above, you can see where any manufacturing defect or imperfection along the way could have drastic consequences to the effectiveness of the touch performance.

Figure 5: Example Sensor Patterns all Yield an X/Y Crossing for Signal Detection.

Understanding the hardware and sensor construction details should give readers a much more detailed understanding of the engineering ingenuity required to produce a well performing touchscreen product. While many users simply want their phone interface to perfectly interpret what their finger is trying to input, there is a very sophisticated design lying behind the touch system in their products; the key is to design the products so that it appears seamless and simple to the user. Everything from pattern design, ITO deposition, materials selection, LCD choice, and touch controller analog and filtering performance all play a critical role in delivering a world-

Figure 6: Example Touch Controller, Found in the Barnes & Noble Color Nook E-Reader (Cypress Semiconductor Controller).

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class touch experience and a seamless user experience. We look forward in our next article to share with you how, once the hardware senses a touch signal, the user’s input is interpreted all the way to the movement of icons on the screen; the software portion of a touchscreen is equally as intriguing as the hardware portion. Until then, we wish you a happy touchscreen user experience.

About the Authors

Steve Kolokowsky is currently working on touchscreen solutions for Cypress Semiconductor. He has over 20 years of experience creating embedded solutions and software. Steve has been involved with Cypress’ TrueTouch solutions and USB solutions including Cypress’ best-selling USB mass storage chip, the AT2LP.

Prior to Cypress, Steve worked for Cirrus Logic creating DSP tools and development kits.

Steve has written over 40 technical articles that have been published in at least six languages. He has over 10 patents issued and several more applications pending.

Trevor Davis is currently the Director of Marketing & Applications for Cypress’s Consumer and Computation Division (CCD) focused on User Interface in consumer products. Trevor received his undergraduate degree from the United States Air Force Academy and also holds his Masters in Business Administration. Trevor has worked in high technology positions for the military, nonprofit, and commercial sectors for the past 15 years and is fascinated by the speed of innovation in User Interface products. ■

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EEWeb Pulse - Volume 22

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