EEWeb Pulse - Issue 34, 2012

PULSE EEWeb.comIssue 34

February 21, 2012

Geir FørreEnergy Micro

Electrical Engineering Community

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TABLE O

F CO

NTEN

TSTABLE OF CONTENTS

Geir Førre 4ENERGY MICRO

Developing the Leopard Gecko and 8Giant Gecko MicrocontrollersBY GEIR FØRRE

Featured Products 10Are You Gaining What You Should From Your Antenna?BY BRIAN PETTED WITH LS RESEARCH

Dynamic Range: Important When 20 Choosing A Source Measurement UnitBY ROBERT GREEN WITH KEITHLEY

RTZ - Return to Zero Comic 21

Energy Micro’s CEO describes their line of energy-efficient microcontrollers and what sets them apart from the rest.

Interview with Geir Førre - President and CEO

Brian Petted walks us through key antenna design considerations for choosing the optimal antenna.

Robert Green outlines the evolution of SMUs and the importance of dynamic range testing on these devices.

12


INTERVIEWFEA

TURED IN

TERVIEW

Energy Micro

Geir Førre

Geir Førre - President and CEO

How did you get into electronics/engineering and when did you start?I am an engineer and entrepreneur at heart and my whole life has

been about making and building things, in both my professional and my private life. I can’t say exactly what it was that led me to become an electronics engineer; maybe

my father being an electrician and my older sister becoming an electronics engineer influenced my decision.

Can you tell us about your work history/journey to becoming the President and CEO of Energy Micro?After earning my MSEE in microelectronics, I started my professional career as a researcher at SINTEF, a large multi-technology research institution. There, I was a part of a group doing advanced mixed-signal IC design for a variety of applications including radiation sensors, high temperature ICs for oil well instrumentation and highly integrated radio ICs. In 1996, after four years at SINTEF, two colleagues and I started Chipcon.

Can you tell us about your work as co-founder, president and CEO of Chipcon?When we started Chipcon in 1996 I think it was a little bit by chance that I became the CEO. In the beginning we were all basically doing the same things, and it wasn’t until a few years later that I adopted more of a leadership role. I began to enjoy the leadership and strategic aspects of my job more and more, which I believe is a key reason why I kept developing in that position and remained as the CEO until and after Chipcon was acquired by Texas Instruments 10 years later.

How were you able to develop it into the market leader in low-power RF solutions only a decade after its founding in 1996?It actually only took between six


INTERVIEWFEA

TURED IN

TERVIEW

and seven years. During the first three to four years we only did consultancy services and custom ASIC projects. We slowly started restructuring the business from ASIC to RF ICs in 1999, and by 2003 this transition was complete. By 2005 we had already become the market leader. I think the one single reason why we were able to achieve this was our speed of innovation. Compared to our competitors, we brought newer, better products to market significantly faster. We were able to maintain this high speed of innovation because the company had very clear vision, direction and goals, which created an energetic atmosphere within a group of people who really wanted to succeed.

What were your personal and professional goals after selling Chipcon to Texas Instruments in 2006?At the time I think my only goal was to successfully integrate Chipcon into Texas Instruments. Looking back, I think the first six months after selling Chipcon were the busiest of my life. That period of time was very hard, both physically and mentally. It was physically difficult due to the long hours and extensive travelling, and mentally difficult because many of the processes and cultural elements that made Chipcon what it was could not continue unchanged within a much larger company like TI. I have to give a lot of credit to TI for how well it did integrating Chipcon, and how well it manages its business overall. The way the company treats its people is also an example to be followed.

Once I started to get my head above

water, I began to think about the future. Should I remain within TI (which was not a bad alternative) or should I do something else? I think it was at this time I realized that I really am an entrepreneur at heart and I love being the underdog and fighting to become the world leader in a particular industry. The only way to put myself into such a position again was to start from scratch once more.

The most important thing we can do to maintain and

strengthen the leading position we have is to

continue to be the most innovative company

in our industry.

I resigned from TI without knowing much more than the fact that I wanted to start a new adventure. It took me another eight months before the idea of Energy Micro became a reality.

What have been some of your strengths that have helped you get to where you are today?First of all, I have a lot of weaknesses. But I do have a few key strengths that make me a good entrepreneur: I believe I am a visionary who is very persistent. These two qualities

allow me to set clear direction and goals to do what it takes to get there.

Do you have any tricks up your sleeve? I would refer to my previous answer. Very few companies (either start-up or mature) have well defined visions and goals. If you do not know where you want to go, how on earth can you get there? A company with a clear idea of its goals has the best recipe for a great future. Energy Micro’s 2020 goal is to reach one billion dollars in revenue. This is 100 times more than we have today.

Do you continue to maintain an active role in product development? If so, how?I was a decent analog IC designer many years ago, but I am too rusty now to really contribute anything. But with regard to the overall product roadmap and product strategy, I continue to contribute very strongly.

Can you tell us more about Energy Micro and the technology it is developing?The original mission of Energy Micro when the company was founded in 2007 was to make the world’s most energy efficient microcontrollers based on 32-bit ARM technology. There were (and still are) three industry trends that all indicated that this could be a very successful mission: 1) More and more applications are becoming battery-operated, which requires better low-energy solutions. 2) Electronic products are continuously becoming more advanced, which effectively moves applications from 8 and 16-bit architectures to 32-bit architectures.


INTERVIEWFEA

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3) Unlike before, software development costs today dominate electronic product development. Customers therefore prefer standardized ARM architectures over proprietary architectures because the software code can be reused to a higher degree.

During the first two years we brought to market the first family of EFM32 energy-friendly microcontrollers which consume one fourth as much energy as any other 8, 16 and 32 bit microcontrollers. Today we provide 180 different EFM32 variants divided into five main families of products, and we are winning more than one new customer every day, which affirms our 2007 assumptions.

Has the company changed since it was established in 2007?Chipcon had a very good company culture, which I believe was essential for what the company achieved. Therefore, when Energy Micro was founded I was obsessed with the idea that we needed to create a fantastic company culture. After about half a year, and with around 15 people recruited, I asked myself the question, “How can I describe the culture of Energy Micro, and is it actually fantastic?” I found I couldn’t really answer the question. I have since acknowledged that a culture is not something that you can establish right from the start. The culture is, rather, the result of a group of people working together to achieve common goals, and all the shared pride that accumulates during the journey. This will and should continuously change the company.

How can Energy Micro continue to be a leading company in the future?The most important thing we can do to maintain and strengthen the leading position we have is to continue to be the most innovative company in our industry. The companies that, over time, manage to stay in front will always have the best chance to be tomorrow’s winner.

Can you tell us about some of the new technologies Energy Micro is working on in the radio industry? As well as our microcontrollers, we also started to develop the world’s most energy-friendly radios (EFR) two years ago. The background to this decision was simply that most low-energy microcontroller applications also need some kind of radio solution; and thanks to the Chipcon experience, we already had tremendous insight into the RF chip industry. When EFRs come to market next year it will reduce the energy consumption of RF ICs by at least a factor of four compared to any other solutions available today. It will at the same time support a large number of frequency bands and a large number of different radio protocols, including BLE, ZigBee, IEEE 802.15.4 and many more.

What challenges do you foresee in our industry?The semiconductor industry is of enormous value to society. Think how much service and productivity a Smartphone provides, and yet you can buy it for a few hundred bucks. The portion of this that ends

up as revenue to the semiconductor companies is just a fraction, despite the enormous R&D costs associated with developing the chips involved. Our industry is suffering from the fact that despite such huge investments in R&D, the margins remain moderate to low. This fact is the underlying reason why so many big semiconductor companies are struggling and why so few VCs today are investing in start-ups in the sector. The positive flip side of this is that great companies that are able to continue to invest heavily in new innovation will hopefully have an even brighter future.

What are your goals for the near future?My focus is completely on making Energy Micro a very successful venture and I do not spend much time on anything else. However, there is one thing that I am pretty sure of: that I will not start another company. When Energy Micro has become a great success I will have already turned 50. To start a company with ambitions like Energy Micro demands so much dedication and hard work that I doubt I’d be able to do it a third time. I will surely not retire though; I believe I will work until my very last day. Now and then I get inspired by what an American president once said: “First you learn, then you earn, and last you serve.” ■

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PROJECTFEA

TURED PRO

JECT

By Geir Førre

Our most recent project at Energy Micro was the development of the Leopard Gecko and Giant Gecko EFM32 energy friendly microcontrollers. We designed them specifically for use in ultra-low power applications with high memory needs, and based them on the 32-bit ARM Cortex M3 processor core.

The Gecko microcontrollers target the growing category of products that need to operate over a period of

years without external power, battery charges or operator intervention: applications such as smart metering, building automation, security systems, portable health and fitness equipment and smart accessories.

We chose the name because in real life a Gecko uses only 10% of the energy compared to mammals of same size while still being active and ready to react.

A measure of our success in design terms is that the resulting devices have been benchmarked as consuming just a quarter of the energy of 8-, 16- and 32-bit alternatives. This equates to extending the lifetime of a typical 3V coin cell battery by around 300%.

Part of this achievement entails offering a large number of configuration options: Leopard and Giant Gecko offer 100 additional variants so designers can choose exactly the right combination of memory, processing power and peripherals for their needs.

We also put in place 10 key technological innovations that combine to offer engineers new ways of reducing energy consumption: we call them the ‘10 Gecko technology factors.’

The first of these is, of course, very low active power consumption. At 32MHz with a 3V power supply, the Gecko technology enables the MCU to consume only 150μA/MHz.

But perhaps counter-intuitively, using a more powerful core also Figure 1: Gecko MCUs

Deve

lopingthe Leopard Gecko

and Giant GeckoMicrocontrollers


PROJECTFEA

TURED PRO

JECT

helps. The Cortex-M3 can execute tasks within fewer clock cycles than less capable devices. This reduces the CPU active period and hence the overall energy consumption.

The third imperative is to minimize the time spent in the frequent transitions between sleep and active modes. Little or no real work is done during these transitions, and by reducing the wake-up time from deep sleep to 2μs, the Gecko microcontrollers consume as little energy as possible before processing starts.

A further area for optimization is to reduce standby current as much as possible, and this is the focus of the fourth, fifth and sixth Gecko technology factors.

EFM32 microcontrollers have five efficient energy modes, giving system designers the utmost flexibility in optimizing their products.

The devices also combine ultra low power technology with clever power management to reduce energy usage in standby modes while still performing basic operations. The Deep Sleep mode uses only 0.9μA with full system retention and the RTC still running, while in Shutoff mode the consumption is only 20nA.

The same active power reduction approach is taken in peripheral design: for instance an on-chip 12-bit 1MSPS ADC draws only 350μA, while the Energy Micro LCD controller can drive 4 x 40 segments at only 0.55μA.

Technology factors seven and eight both concern peripheral usage. Gecko MCU peripherals can function autonomously, without using the CPU, allowing the MCU to remain in sleep mode more frequently. Not only this, a ‘peripheral reflex’ system allows the peripherals themselves to be directly interconnected, allowing the designer to implement relatively

complex functions without CPU intervention.

Finally, the EMF32 series is backed by two system design facilities that help engineers optimize their designs. An advanced energy monitoring function allows real-time measurement and review of a prototype’s current consumption profile. Just as importantly, the Simplicity Studio and energyAware design and debug tools aim to cut design cycles in half, while focusing squarely at minimizing energy consumption.

Bringing the Leopard Gecko and Giant Gecko EFM32 MCUs to market last year was a proud achievement for everyone at Energy Micro. But as in any technology business, we cannot stand still. At the moment, we are already well under way with our next development: a major new product upgrade that will not simply address customer needs today, but also anticipate their aspirations in the future. ■

Figure 2: Block Diagram


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This article is an overview of important antenna design considerations. The design considerations include system requirements, antenna selection, antenna placement, antenna element design/simulation and antenna measurements. A center-fed dipole antenna is the design/simulation example used. Measurement discussion includes reflection parameter measurements and directive gain measurements.

Antenna Requirements

Gain and Communication Range. With the advent of prolific wireless communications applications, system designers are in a position to consider the placement and performance of an antenna system. The first step in establishing antenna requirements is determining the desired communication range and terminal characteristics of the radio system (transmit power, minimum receiver sensitivity level). Given those parameters, one can ascertain the amount of gain or loss required to maintain the communication range by using the Friis Transmission formula [1]:

This relation is only valid for free-space propagation, but illustrates the important role of the antenna gain in the maximization of the receive-to-transmit power ratio or system link gain.

Antenna Size and Clearance. Antenna gain (or loss) must be part of a trade-off study between performance and the physical realization considerations of size, placement and clearance (distance from obstructions).

Are You Gaining

From Your Antenna?

What You Should

Brian PettedChief Technical Officer

P received power [W]

P transmitted power [W]

c speed of light [ ]

g transmit antenna gain [ ]

g received antenna gain [ ]

f cyclic frequency [Hz]

r communication range [m]

PP

(4 rf)c g g

t

r2

2t r

sm

WW

r WW

r

t

t

=

/

/

/

/

/

/

/

r


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One basic antenna relationship presented below shows that antenna gain, g, and the antenna effective aperture (area) are directly proportional—roughly indicating that antenna gain is proportional to the physical size of the antenna [2].

resistances and losses in the antenna element conductor and dielectric structures. The mismatch loss can be ascertained through simulation or measurement of the antenna’s input impedance or reflection coefficient, Г. The directivity, D, is a description of the gain variation, a function of link axis angle(s) or angle(s) of arrival/departure as described by the standard spherical coordinate system.A 4

g; wavelength [m] f

ce

2

= = =rm

m

Another basic antenna relationship shows the Fraunhofer or Rayleigh distance, d, at which the near-field/far-field transition zone exists. Ideally, there should exist a free-space clearance zone around the antenna of at least d. The largest dimension of the antenna, D, and the operating wavelength determine this distance [3].

d > 2D ; r >> D ; r >>2

mm

For example, if the largest dimension of the antenna is half of a wavelength, the minimum clearance zone is half of a wavelength. This serves as a basic guideline. However, in many physical realizations, this clearance zone is compromised and the effects must be determined through simulation or empirical measurement.

d >2 2

2

2

=m

mm

c m

Antenna Gain Details. Antenna gain is defined as the ratio of radiated power intensity relative to the radiated power intensity of an isotropic (omni-directional) radiator. Power intensity is the amount of radiated power per unit solid angle measured in steradians [sr] [ 4]. The sphere associated with the isotropic radiator has a steradian measure of 4π steradians and serves as the normalization reference level for antenna gain.

g UU

4PU ; [W/sr]

[W/sr]t

isotropic

rad

t

rad= =r

The antenna gain expression can be expanded further to reveal other factors that contribute to the overall antenna gain. The radiation intensity for the antenna is a function of the antenna efficiency, η , and the directivity, D. The antenna efficiency is a product of the reflection efficiency or mismatch loss and the losses due to the finite

g P4 [ D[ , )]

P4 [ D( , )]

P4 [(1 | | ) D( , )]

tt t

refl. cd

t

2cd= = =

-r h z i r h h z i r h z iC

g P4 [ D[ , )]

P4 [ D( , )]

P4 [(1 | | ) D( , )]

tt t

refl. cd

t

2cd= = =

-r h z i r h h z i r h z iC

Antenna Gain Patterns. Ideally, antenna patterns are displayed as a three-dimensional plot as shown in Figure 1. This 3-D plot is often constructed from multiple cross sections known as conical cuts. A typical conical cut is formed by holding the elevation angle, θ, constant and measuring the pattern over a complete revolution of the azimuthal angle, φ. Secondly, a separate plot is generally made for each component of the electric field or polarization (Eφ-horizontal or Eθ-vertical). Examples of conical cuts are presented in Figure 2. One example is an omni-directional antenna with equal polarizations, and the second example is a directional antenna with distinct polarization responses.

Figure 1: Antenna gain pattern displayed in 3-dimensions.


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Since most antenna patterns are not necessarily omni-directional, the description of antenna gain is fairly complex. In order to serve a system analysis in terms of determining communication range or system gain, typically the minimum, maximum and average gain over the entire pattern of a particular cut is used as the singular antenna gain value in the Friis transmission formula.

However, there may be an interest in determining the distribution of communication ranges and system gains, given the non-uniform nature of a directional antenna that is used in an omni-directional application. In those cases, probability density functions (pdfs)

can be associated with antenna patterns, both conical cuts and 3-D patterns [5]. Even though the directional antenna patterns are deterministic, the fact that their application is omni-directional with a random link axis angle makes the antenna gain a random variable with respect to communication range and system gain analyses. Presented in Figure 3 is the pdf associated with both the omni- and non-uniform patterns presented in the left-hand side of Figure 3. Presented on the right-hand side of Figure 3 is the complementary-cumulative density function (ccdf), which is derived from the pdf and indicates the probability that the antenna can provide a minimum level of gain, given a random link axis angle.

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Vertical Polarization Gain (dBi) min:+0.0 max:+0.0 avg:+0.0

Horizontal Polarization Gain (dBi) min:+0.0 max:+0.0 avg:+0.0

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Horizontal Polarization Gain (dBi) min:+0.0 max:+0.0 avg:+0.0

Figure 2: Conical Cuts for Omni-Directional (Left) and Directional Antennas (Right).

Figure 3: Gain pdf (left) and associated ccdf (right).

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Gain Coverage Probability Density Functions (pdf)

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Gain Coverage Probability

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v pdfh pdf

v ccd1h ccd1


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Note for the case of the omni-directional antenna, the pdf is an impulse since the gain is single-valued and has no real distribution. The omni-directional case presents an interesting step-function ccdf which shows that the probability of having a directive gain at least as large as the abscissa is one for gains less than the fixed gain value.

Antenna Topologies

There can be many possible topologies or structures for an antenna. An interesting set of structures are those which evolve from the basic half-wave dipole. The evolution is shown in Figure 4.

to arrive at a final design. Secondly, the electromagnetic relations associated with most antennas are not closed form and do not yield dimensional synthesis equations. Therefore, in order to design and validate an antenna prior to fabrication, it is beneficial to simulate the antenna using an electromagnetic field solver that can predict the behavior of radiating systems.

One such solver, CST Microwave Studio® [6], offers many methods of solution that can simulate open-boundary, radiating structures. One example is presented which shows the relative utility of the simulation tool. Presented in Figure 6 is the input page for a 2.4 GHz sleeve dipole antenna. The input page contains the dimensional and material parameter inputs required to carry out the simulation.

Figure 4: Antenna evolution from the half-wave dipole (left): quarter-wave monopole over a ground plane (center), L-antenna (right).

Starting with the half-wave dipole, the lower element of the dipole can be realized by a reflected image of the upper element onto a ground plane (using electric field boundary conditions and/or image theory). The monopole can be folded over, however, with degradation in impedance match and gain. The degradation due to matching can be recovered by feeding the antenna at a different point along the resonant length of the antenna (recall the impedance variation of a transmission line with a standing wave present). This results in the inverted “F” antenna. The elements may be extruded from the wire form to a planar form to realize an increase in impedance and gain bandwidth, but with a small degradation in gain. These additional evolutions are presented in Figure 5.

Antenna Design and Simulation

The initial design of an antenna can arise from a set of dimensional formulas based on closed-form electromagnetic relations. However, in practice, these antennas require some empirical adjustment/tuning steps

Figure 5: Inverted “F” Antenna evolution from the L-antenna by feeding the antenna at a more favorable impedance point (left): extruded version of Inverted F antenna to produced Planar Inverted F antenna or PIFA (right).

Figure 6: Sleeve Dipole Design Input into CST Microwave Studio simulator.

y/4

y/4

z

y

Name Value Description

L_cable 500 Cable length

L_center 925 Top dipole arm length

L_shield L_center Bottom dipole arm (sleeve) length

R_center 10 Coax center conductor radius

R_dipole 50 Bottom dipole element inner radius

R_shield 3.331 *R_center Coax shield inner radius D=d*10^(50*sqrt(er)/138=33.31

t_shield 5 Shield Thickness

L_total L_cable+L_center+L_shield 2350 mils


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Upon completion of the electromagnetic simulation, the radiation pattern of the electric field is available as a 3-D plot and as conical cuts. Further, the simulator predicts the input reflection coefficient and represents it as a scattering parameter (S11). The simulator provides all of the essential information about the antenna prior to its physical realization in order to pre-validate the design approach. Figure 7 shows the predicted reflection coefficient and driving point impedance.

coefficient of the antenna input port or driving point. A Vector Network Analyzer (VNA) measures the reflection coefficient and associated driving point impedance. Care must be taken during this measurement to ensure that the antenna is radiating and not being disturbed by any surrounding objects. Ideally, this measurement should be performed in an anechoic chamber. However, with sufficient separation between the antenna and any perturbing obstructions, this measurement can typically be performed within a normal laboratory environment.

In order to initially validate the antenna design, the reflection coefficient and associated driving point impedance must be such that the antenna is reasonably matched to the system impedance (generally 50 ohms).

Once it has been established that the antenna is matched to the system impedance, the radiation pattern must be measured to compete the final steps of design validation. The measurements are performed in an anechoic chamber by exciting the antenna under test with a known transmit source power and measuring the received power, received voltage or electric field intensity at a fixed distance. A photograph of an antenna under test in a 3-meter anechoic chamber is presented in Figure 10.

The antenna is swept through a series of conical cuts in an effort to compare them to simulated results or to build a set of cuts to assemble into a 3-D gain pattern. The absolute received signal is normalized either by the conducted power applied to the antenna or compared to a known reference such as a half-wave dipole. Both

Figure 7: Sleeve Dipole reflection coefficient (left) and impedance prediction. (right).

Figure 8: Sleeve Dipole 3-D antenna pattern for θ-directed Electric Field component.

Antenna Design Validation and Measurement

With the antenna synthesized and realized, the design must be validated through measurement. The first necessary measurement is to measure the reflection

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S-Parameter Smith ChartS-Parameter Magnitude in dB

2400.000000(82.168261, 18.111261) Ohm

2300

2700

0.15 0.3 0.5 0.75 1 1.3 1.6 2 2.7 4 6 10

333

1

2450.000000(74.987673, 26.127237) Ohm2

2500.000000(70.531508, 31.315733) Ohm

S1,1 (50.1 Ohm)S1,1

3

2515.3

d=5.3282

Frequency/MHz

Frequency/MHz

d=140.34

-5.9893

-11.318


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polarization cases are measured. With the set of pattern data at hand, the measurements can also be examined against the system requirements in terms of minimum, maximum, and average gain, or against gain distribution requirements, if applicable.

Figure 9: Associated Conical Cuts for θ-directed Electric field over angle φ at fixed angle θ=90 degrees (left) and θ -directed Electric field over angle θ at fixed angle φ=0 degrees (right).

Figure 10: Typical antenna pattern measurement configuration within an anechoic chamber.

Closing Remarks

Antennas provide the primary interface between the radio and propagation environments. The antenna

requires special considerations in terms of performance requirements, design constraints, design and realization. Specification of the antenna gain and relating those requirements to the system performance (in terms of range and system link gain) is a foundation for the design goals of the antenna. During the antenna topology/structure selection process, consider packaging constraints in terms of the size, location and possible obstructions; be prepared to compromise performance versus package conformance.

Ideally, one should use a simulation tool to assess the performance of the antenna prior to realization, not only to gauge the fundamental performance of the antenna, but also to check the effects of antenna compaction, obstructions and other compromised parameters. The final physical realization and consequent measurement of input terminal reflection/impedance and antenna gain complete the design process. Often times, the measurement results require the antenna structure to be modified to empirically optimize its performance.

References:

[1] Harald Friis, “A Note on a Simple Transmission Formula,” Proc. IRE, 34, 1946, pp. 254-256.

[2] Theile and Stutzman, “Antenna Theory and Design”, Second Edition, John Wiley and Sons, 1998, p. 79.

[3] Theile and Stutzman, “Antenna Theory and Design”, Second Edition, John Wiley and Sons, 1998, p. 30.

030

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Phi=0 Phi=180

Fairfield ‘ff_2450.0000 [1]’ Realized Gain_Theta[Theta]Fairfield ‘ff_2450.0000 [1]’ Realized Gain_Theta[Phi]; Theta=90.0º

0330

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270

240

210180

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Frequency = 2450Main lobe magnitude = 1.6 dBMain lobe direction = 93.0 degAngular width [3 dB] = 77.2 deg

Frequency = 2450Main lobe magnitude = 1.5 dBMain lobe direction = 272.0 deg


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[4] Theile and Stutzman, “Antenna Theory and Design”, Second Edition, John Wiley and Sons, 1998, pp. 39-43.

[5] B. Petted, “Antenna Gain Considerations in Communications System Range Analysis” Seminar in Microwave Engineering, Marquette University, March 20, 2009.

[6] CST Microwave Studio®, CST of America, Framingham, MA 01701.

About the Author

Brian Petted is the Chief Technology Officer of L.S. Research, LLC—a wireless product development company and EMC testing laboratory. Mr. Petted holds a BSEET degree from the Milwaukee School of Engineering (MSOE) and a MSEE from Marquette University. Other industrial experience includes RF integrated circuit work at Rockwell-Collins Avionics and Harris Government Communications Systems. ■

http://bit.ly/nKLRXo

Low-Noise 24-bit Delta Sigma ADCISL26132, ISL26134The ISL26132 and ISL26134 are complete analog front ends for high resolution measurement applications. These 24-bit Delta-Sigma Analog-to-Digital Converters include a very low-noise amplifier and are available as either two or four differential multiplexer inputs. The devices offer the same pinout as the ADS1232 and ADS1234 devices and are functionally compatible with these devices. The ISL26132 and ISL26134 offer improved noise performance at 10Sps and 80Sps conversion rates.

The on-chip low-noise programmable-gain amplifier provides gains of 1x/2x/64x/128x. The 128x gain setting provides an input range of ±9.766mVFS when using a 2.5V reference. The high input impedance allows direct connection of sensors such as load cell bridges to ensure the specified measurement accuracy without additional circuitry. The inputs accept signals 100mV outside the supply rails when the device is set for unity gain.

The Delta-Sigma ADC features a third order modulator providing up to 21.6-bit noise-free performance.

The device can be operated from an external clock source, crystal (4.9152MHz typical), or the on-chip oscillator.

The two channel ISL26132 is available in a 24 Ld TSSOP package and the four channel ISL26134 is available in a 28 Ld TSSOP package. Both are specified for operation over the automotive temperature range (-40°C to +105°C).

Features• Up to 21.6 Noise-free bits.

• Low Noise Amplifier with Gains of 1x/2x/64x/128x

• RMS noise: 10.2nV @ 10Sps (PGA = 128x)

• Linearity Error: 0.0002% FS

• Simultaneous rejection of 50Hz and 60Hz (@ 10Sps)

• Two (ISL26132) or four (ISL26134) channel differential input multiplexer

• On-chip temperature sensor (ISL26132)

• Automatic clock source detection

• Simple interface to read conversions

• +5V Analog, +5 to +2.7V Digital Supplies

• Pb-Free (RoHS Compliant)

• TSSOP packages: ISL26132, 24 pin; ISL26134, 28 pin

Applications• Weigh Scales

• Temperature Monitors and Controls

• Industrial Process Control

• Pressure Sensors

ADC

PGA1x/2x/64x/128x

INTERNAL CLOCK

SDO/RDY

SCLK

DVDDAVDD

DGNDAGND

XTALIN/CLOCK

VREF+

EXTERNAL OSCILLATOR

XTALOUT

VREF-A0 A1/TEMP

AIN1+AIN1-

AIN2+AIN2-

AIN3+AIN3-

AIN4+AIN4-

INPUTMULTIPLEXER

ISL26134 Only

CAP

CAP

GAIN1GAIN0

PWDN

SPEED

DGNDDGND

NOTE for A1/TEMP pin: Functions as A1 on ISL26134; Functions as TEMP on ISL26132

FIGURE 1. BLOCK DIAGRAM

September 9, 2011FN6954.1

Get the Datasheet and Order Samples

http://www.intersil.com

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.

http://bit.ly/nHxRhB


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Figure 1: An example SMU operating range showing operation in all four-quadrants.

Important When Choosinga Source Measurement Unit

Robert GreenSenior Market Development ManagerDynamic

Range

Source measurement units (SMUs) are instruments that can source current and measure voltage, or source voltage and measure current. Since their introduction more than 20 years ago, they have evolved into multi-purpose instruments that meet the needs of an expanding array of test applications:

• semiconductor device fabrication, process development, and product research/design

• production verification of ultra-low power, electronic products such as implantable pacemakers

• production and development of new advanced materials for devices such as solar cells and HBLEDs

SMU instruments are capable of four-quadrant operation (Figure 1), acting as a positive or negative DC source or as a sink (load). They also provide highly repeatable measurements, typically with 5-1/2 or 6-1/2 digit resolution. And because SMUs can sweep the output voltage or current, test engineers use SMU instruments in automated test systems that determine the I-V characteristics of semiconductor devices. For testing

higher power devices, SMU instruments can generate high current pulses to test devices without dumping excess heat into the device and raising the device’s temperature.

For testing many types of devices, you need test equipment that can operate over a wide range of signal

+0.1A

– 0.1A0A

– 1A

+1A

+1.5A

– 1.5A

–200V +200V–180V +180V–20V +20V–5V +5V0V

+10A

– 10A

III

IVIII

DC Pulse


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levels. For example, devices such as power MOSFETs are designed to have very low resistance and handle very large currents when turned on, but have very high resistance and allow nearly zero current to flow when turned off. When turned on, this current can be as high as tens of amps; when off, this current nears less than one nano-amp.

Similarly, you need a wide dynamic range when characterizing power diodes and high brightness LEDs. When a forward bias voltage below the threshold value is applied to these devices, device currents are very low. As voltage is increased from 0V to the threshold, device current goes from less than one microamps to more than one milliamp. As the bias voltage reaches and exceeds the threshold, test currents increase very rapidly, reaching as high as tens to hundreds of amps depending on the device. Using a single piece of test equipment that can make accurate measurements over this wide range is desirable because it makes the test setup less complex and less expensive.

Unfortunately, despite claims to the contrary, the dynamic range of component SMUs from most manufacturers is several decades smaller than the most sensitive instrument SMUs. On the high end, they are limited by

how much current they can source, usually topping out at 100 milli-amps. On the low end, these SMUs generally do not have enough shielding to prevent the noise generated by the circuitry from affecting the low-level measurements. As a result, most component SMUs do not have current ranges lower than 10 micro-amps.

To avoid these limitations, make sure that the SMU you buy has the dynamic range that you’ll need. For more information on this topic, see the Keithley backgrounder, “Rapidly Expanding Array of Test Applications Continues to Drive Source Measurement Unit Instrument Technology.” You’ll find it here.

About the Author

Robert Green is a Senior Market Development Manager at Keithley Instruments, (part of the Tektronix T&M portfolio), focusing on low level measurement applications. During his 20-year career at Keithley, Mr. Green has been involved in the definition and introduction of a wide range of products including picoammeters, electrometers, digital multimeters, and temperature measurement products. He received a B.S. in Electrical Engineering from Cornell University and an M. S. in Electrical Engineering from Washington University, St. Louis, Missouri. ■

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EEWeb Pulse - Issue 34, 2012

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